# Patent

## Title
Prokaryotic expression construct

## Abstract

A pro-polypeptide which is useful for the expression of a polypeptide of interest in a prokaryotic cell. Therefore the pro-polypeptide is fused to the N-terminus of the polypeptide of interest. The pro-polypeptide as reported herein provides for improved expression yields and improves the handling of the fusion polypeptide (downstream processing, purification). For example, efficient endotoxin removal is effected while the protein of interest comprising the pro-polypeptide is bound e.g. to an affinity chromatography material. Thereafter the pro-polypeptide can efficiently be cleaved from the polypeptide of interest by the incorporated protease cleavage site with the cognate protease.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This Application claims priority under 35 U.S.C. §119 to European Application No. EP 10008996.0 filed Aug. 30, 2010, and European Application No. EP 10187663.9 filed Oct. 15, 2010, the disclosures of which are incorporated herein by reference.
SEQUENCE LISTING
The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 18, 2012, is named P4518.txt and is 111,087 bytes in size.
FIELD OF THE INVENTION
Herein is reported an expression construct for the production of a polypeptide in a prokaryotic cell. The expression construct comprises a pro-polypeptide comprising in N- to C-terminal direction the dipeptide GS, an amino acid tag, the dipeptide GS, and a protease cleavage site.
BACKGROUND OF THE INVENTION
Expression systems for the production of recombinant polypeptides are well-known in the state of the art and are described by, e.g., Marino, M. H., Biopharm. 2 (1989) 18-33; Goeddel, D. V., et al., Methods Enzymol. 185 (1990) 3-7; Wurm, F., and Bernard, A., Curr. Opin. Biotechnol. 10 (1999) 156-159.
Polypeptides, such as antibodies and antibody fusions, for use in pharmaceutical applications are generally produced in mammalian cells such as CHO cells, NS0 cells, SP2/0 cells, COS cells, HEK cells, BHK cells, PER.C6TM cells, or the like. The elements of an eukaryotic expression plasmid are generally a prokaryotic plasmid propagation unit, for example for E. coli, comprising a prokaryotic origin of replication and a prokaryotic selection marker, an eukaryotic selection marker, and one or more expression cassettes for the expression of the structural gene(s) of interest each comprising a promoter, a structural gene, and a transcription terminator including a polyadenylation signal. For transient expression in mammalian cells a mammalian origin of replication, such as the SV40 Ori or OriP, can be included. As promoter a constitutive or inducible promoter can be selected. For optimized transcription a Kozak sequence may be included in the 5′ untranslated region. For mRNA processing, in particular mRNA splicing and transcription termination, mRNA splicing signals, depending on the organization of the structural gene (exon/intron organization), may be included as well as a polyadenylation signal.
Other polypeptides for use in pharmaceutical applications, e.g. insulin, interferon alpha-2, somatotropin, interleukin-2, GM-CSF and Reteplase, can be produced in prokaryotic cells, yeast, and mainly E. coli. The elements of an E. coli expression plasmid are generally an origin of replication, a selection marker, and one or more expression cassettes for the expression of the structural gene(s) of interest. An expression cassette generally comprises a promoter, a structural gene, and a transcription terminator. As promoter a constitutive or inducible promoter can be used. For optimized transcription a Shine-Dalgarno-Sequence or a variant thereof preceding the start codon of mRNA may be included in the 5′ untranslated region.
SUMMARY OF THE INVENTION
Herein is reported a pro-polypeptide which is useful for the expression of a polypeptide of interest in a prokaryotic cell. Therefore the pro-polypeptide is fused to the N-terminus of the polypeptide of interest. The pro-polypeptide as reported herein provides for improved expression yields and improves the handling of the fusion polypeptide (downstream processing, purification). For example, efficient endotoxin removal is effected while the protein of interest comprising the pro-polypeptide is bound e.g. to an affinity chromatography material. Thereafter the pro-polypeptide can efficiently be cleaved from the polypeptide of interest by the incorporated protease cleavage site with the cognate protease.
Herein is reported as one aspect a pro-polypeptide comprising in N- to C-terminal direction

    
    
        a first dipeptide with the amino acid sequence GS,
        an amino acid sequence tag,
        a second dipeptide with the amino acid sequence GS immediately adjacent to
        an enzymatic cleavage site.
    
    


In one embodiment the pro-polypeptide comprises a leading amino acid sequence N-terminal to the first dipeptide with the amino acid sequence GS. In another embodiment the leading amino acid sequence has a length of at least two amino acid residues and at most of twenty amino acid residues. In a further embodiment the leading amino acid sequence has a length of at least two amino acid residues and at most of ten amino acid residues. In also an embodiment the leading amino acid sequence is a polypeptide with an amino acid sequence selected from SEQ ID NO: 1-8. In a further embodiment the leading amino acid sequence is a polypeptide with an amino acid sequence selected from SEQ ID NO: 1-6.
In one embodiment the pro-polypeptide is consisting in N- to C-terminal direction of

    
    
        a leading amino acid sequence,
        a first dipeptide with the amino acid sequence GS,
        an amino acid sequence tag,
        a second dipeptide with the amino acid sequence GS immediately adjacent to
        an enzymatic cleavage site.
    
    


A further aspect as reported herein is a fusion polypeptide comprising in N- to C-terminal direction

    
    
        optionally a leading amino acid sequence,
        a first dipeptide with the amino acid sequence GS,
        an amino acid sequence tag,
        a second dipeptide with the amino acid sequence GS immediately adjacent to
        an enzymatic cleavage site, and
        a protein of interest.
    
    


In one embodiment of all aspect as reported before the amino acid sequence tag has the amino acid sequence selected from SEQ ID NO: 9 to SEQ ID NO: 27. In one embodiment the amino acid sequence tag has the amino acid sequence of SEQ ID NO: 11 or SEQ ID NO: 15. In another embodiment the enzymatic cleavage site has the amino acid sequence selected from SEQ ID NO: 28 to 42. In a further embodiment the polypeptide of interest is selected from antibody heavy or light chain, antibody fragment, single-chain antibody, apolipoprotein, apolipoprotein variant, apolipoprotein fusion, interferon, interleukin, insulin, tissue type plasminogen activator variant, colony-stimulating factor, growth hormone, bone morphogenetic protein. In one embodiment the polypeptide of interest has the amino acid sequence of SEQ ID NO: 43 or SEQ ID NO: 44 or SEQ ID NO: 45. In one embodiment the polypeptide of interest is a polypeptide different from the pro-polypeptide as reported herein, i.e. the polypeptide of interest does not comprise an amino acid sequence corresponding to a dipeptide with the amino acid sequence GS directly fused to an amino acid sequence tag. In one embodiment the amino acid at the N-terminus of the polypeptide of interest has a free alpha-amino group after downstream processing. In one embodiment the pro-polypeptide and/or the polypeptide of interest is not glycosylated.
Herein is reported as another aspect a method for producing a polypeptide of interest comprising the following steps

    
    
        a) providing a cell comprising a nucleic acid encoding a fusion polypeptide comprising in N- to C-terminal direction
        
            optionally a leading amino acid sequence,
            a first dipeptide GS,
            an amino acid sequence tag,
            a second dipeptide GS immediately adjacent to
            an enzymatic cleavage site, and
            a polypeptide of interest,
        
        
        b) cultivating the cell,
        c) recovering the fusion polypeptide from the cell or the cultivation medium,
        d) purifying the fusion polypeptide,
        e) enzymatically cleaving the fusion polypeptide and thereby producing the polypeptide of interest.
    
    


In one embodiment the cell is a prokaryotic cell. In another embodiment the cell is an E. coli cell or a Bacillus subtilis cell. In one embodiment the amino acid sequence tag has the amino acid sequence selected from SEQ ID NO: 9 to SEQ ID NO: 27. In one embodiment the amino acid sequence tag has the amino acid sequence of SEQ ID NO: 11 or SEQ ID NO: 15. In another embodiment the enzymatic cleavage site has the amino acid sequence selected from SEQ ID NO: 28 to 42. In also an embodiment the further polypeptide is selected from antibody heavy or light chains, antibody fragment, single-chain antibody, apolipoprotein, apolipoprotein variant, apolipoprotein fusion, interferon, interleukin, insulin, tissue type plasminogen activator variant, colony-stimulating factor, growth hormone, bone morphogenetic protein. In one embodiment the polypeptide of interest has the amino acid sequence of SEQ ID NO: 43 or SEQ ID NO: 44 or SEQ ID NO: 45. In one embodiment the polypeptide of interest is a polypeptide different from the pro-polypeptide as reported herein, i.e. the further polypeptide does not comprise the dipeptide with the amino acid sequence GS directly fused to an amino acid sequence tag.
Herein is reported as a further aspect a kit of parts comprising a nucleic acid comprising in 5′- to 3′-direction

    
    
        a nucleic acid encoding the dipeptide with the amino acid sequence GS,
        a nucleic acid encoding an amino acid sequence tag,
        a nucleic acid encoding the dipeptide with the amino acid sequence GS immediately adjacent to
        a nucleic acid encoding an enzymatic cleavage site.
    
    


One aspect as reported herein is a method for the cultivation of prokaryotic cells, characterized in that

    
    
        the cells are cultivated in a medium comprising glucose, yeast extract, L-leucine, L-proline, L-methionine, Thiamin-HCl, anti foam agent,
        the cells are fed with a first feed solution comprising yeast extract, glycerol, L-methionine, L-leucine and L-proline,
        the cells are fed with a second feed solution comprising L-Proline,
        a potassium hydroxide solution and a glucose solution are used for pH control.
    
    


One aspect as reported herein is a method for the production of a polypeptide, characterized in that

    
    
        cells comprising a nucleic acid encoding the polypeptide are cultivated in a medium comprising glucose, yeast extract, L-leucine, L-proline, L-methionine, Thiamin-HCl, anti foam agent,
        the cells are fed first with a feed solution comprising yeast extract, glycerol, L-methionine, L-leucine and L-proline,
        the cells are fed second with a feed solution comprising L-Proline,
        a potassium hydroxide solution and a glucose solution are used for pH control,
        wherein the polypeptide is recovered from the cells or from the cultivation medium and thereby a polypeptide is produced.
    
    


In one embodiment of the methods as reported herein the addition of the first feed is started at an optical density of about 15 determined at 578 nm, the addition of the second feed is started at an optical density of about 50 determined at 578 nm, and the expression of the polypeptide is induced with IPTG at an optical density of about 90 determined at 578 nm.
In one embodiment of the methods as reported herein the medium comprises about 8.85 g/l glucose, about 63.5 g/l yeast extract, about 2.2 g/l NH4Cl, about 1.95 g/l L-leucine, about 2.9 g/l L-proline, about 0.75 g/l L-methionine, about 17.3 g/l KH2PO4*3H2O, about 2 g/l MgSO4*7H2O, about 25.8 mg/l Thiamin-HCl, about 1.0 ml/l 10% anti foam agent.
In one embodiment of the methods as reported herein the first feed solution comprises about 333 g/l yeast extract, about 333 g/l 85%-glycerol, about 1.7 g/l L-methionine, and about 5 g/l L-leucine and L-proline each.
In one embodiment of the methods as reported herein the second feed solution comprises about 600 g/l L-proline.
In one embodiment of the methods as reported herein the base for pH regulation is a 10% (w/v) KOH solution and the acid is a 75% glucose solution.
In one embodiment of the methods as reported herein the cultivation is at about 25° C.
In one embodiment of the methods as reported herein the cultivation is at a pH between about pH 6.5 and about pH 6.9.
In one embodiment the cultivation is in a volume of about 10 l.
In one embodiment of the methods as reported herein the first feed is started at a rate of 70 g/h.
In one embodiment of the methods as reported herein the second feed is started at a rate of 10 ml/h.
In one embodiment of the methods as reported herein the dissolved oxygen value is kept above 50%. In a specific embodiment the dissolved oxygen value is kept above 50% by increasing stirrer speed, aeration rate, and air pressure in parallel.
In one embodiment of the methods as reported herein the stirrer speed is from about 500 rpm to about 1500 rpm.
In one embodiment of the methods as reported herein the aeration rate is from about 10 l/min to about 20 l/min.
In one embodiment of the methods as reported herein the air pressure is from about 300 mbar to about 500 mbar.
In one embodiment of the methods as reported herein the prokaryotic cell is an E. coli cell.
In one embodiment of the methods as reported herein the polypeptide is apolipoprotein A1. In a specific embodiment the apolipoprotein A1 is tetranectin-apolipoprotein A1 precursor protein.
One aspect as reported herein is a cultivation medium for prokaryotic cells comprising about 8.85 g/l glucose, about 63.5 g/l yeast extract, about 2.2 g/l NH4Cl, about 1.95 g/l L-leucine, about 2.9 g/l L-proline, about 0.75 g/l L-methionine, about 17.3 g/l KH2PO4*3H2O, about 2 g/l MgSO4*7H2O, about 25.8 mg/l Thiamin-HCl, about 1.0 ml/l 10% anti foam agent.
In one embodiment the medium further comprises a first feed comprising about 333 g/l yeast extract, about 333 g/l 85%-glycerol, about 1.7 g/l L-methionine, and about 5 g/l L-leucine and L-proline each.
In one embodiment the medium further comprises a second feed solution comprising about 600 g/l L-proline.
DESCRIPTION OF THE SEQUENCE LISTINGS
SEQ ID NO: 1 to 8 amino acid sequences
SEQ ID NO: 9 to 27 amino acid tags
SEQ ID NO: 28 to 42 protease cleavage sites
SEQ ID NO: 43 to 76 apolipoprotein amino acid sequences
SEQ ID NO: 77 to 78 variant apolipoprotein fusion amino acid sequences
SEQ ID NO: 79 to 84 pro-polypeptide amino acid sequence


DETAILED DESCRIPTION OF THE INVENTION
The herein reported pro-polypeptide is useful for the expression of a polypeptide of interest in a prokaryotic cell. It provides for improved expression yields and improves the handling e.g. during downstream processing and purification. For example, efficient endotoxin removal is effected while the protein of interest comprising the pro-polypeptide is bound e.g. to an affinity chromatography material. Thereafter the pro-polypeptide can efficiently be cleaved from the polypeptide of interest by the incorporated protease cleavage site with the cognate protease.
Herein is reported a pro-polypeptide comprising in N- to C-terminal direction

    
    
        optionally a leading amino acid sequence,
        a first dipeptide GS,
        an amino acid sequence tag,
        a second dipeptide GS immediately adjacent to
        an enzymatic cleavage site.
    
    


The term “amino acid” or “amino acid residue” as used within this application denotes the group of carboxy α-amino acids, which directly or in form of a precursor can be encoded by a nucleic acid. The individual amino acids are encoded by nucleic acids consisting of three nucleotides, so called codons or base-triplets. Each amino acid is encoded by at least one codon. This is known as “degeneration of the genetic code”. The term “amino acid” as used within this application denotes the naturally occurring carboxy α-amino acids comprising alanine (three letter code: ala, one letter code: A), arginine (arg, R), asparagine (asn, N), aspartic acid (asp, D), cysteine (cys, C), glutamine (gln, Q), glutamic acid (glu, E), glycine (gly, G), histidine (his, H), isoleucine (ile, I), leucine (leu, L), lysine (lys, K), methionine (met, M), phenylalanine (phe, F), proline (pro, P), serine (ser, S), threonine (thr, T), tryptophan (trp, W), tyrosine (tyr, Y), and valine (val, V).
The term “polypeptide” denotes a polymer consisting of amino acids joined by peptide bonds, whether produced naturally or synthetically. Polypeptides of less than about 20 amino acid residues may be referred to as “peptides”, whereas molecules consisting of two or more polypeptides or comprising one polypeptide of more than 100 amino acid residues may be referred to as “proteins”. The term “dipeptide” denotes a peptide consisting of two amino acid residues connected to each other with a peptide bond. A polypeptide may also comprise non-amino acid components, such as carbohydrate groups, metal ions, or carboxylic acid esters. The non-amino acid components may be added by the cell, in which the polypeptide is expressed, and may vary with the type of cell. Polypeptides are defined herein in terms of their amino acid backbone structure or the nucleic acid encoding the same. Additions such as carbohydrate groups are generally not specified, but may be present nonetheless. In one embodiment the polypeptide of interest is an apolipoprotein or an apolipoprotein variant/fusion. In another embodiment the apolipoprotein is an apolipoprotein A1 or an apolipoprotein A1 variant/fusion. In a further embodiment the apolipoprotein A1 is fused N-terminally to a tetranectin trimerization domain resulting in an artificial tetranectin-apolipoprotein A1 fusion polypeptide. In one embodiment the polypeptide of interest has an amino acid sequence selected from SEQ ID NO: 43 to SEQ ID NO: 76. In another embodiment the polypeptide of interest has an amino acid sequence selected from SEQ ID NO: 43, or SEQ ID NO: 44, or SEQ ID NO: 45.
The term “leading amino acid sequence” denotes a sequence of amino acids or amino acid residues connected to each other via peptide bonds. In one embodiment the leading amino acid sequence consists of from one to twenty amino acid residues. In another embodiment the leading amino acid sequence consists of from two to fifteen amino acid residues. In a further embodiment the leading amino acid sequence consists of from four to ten amino acid residues. In also an embodiment the leading amino acid sequence has the amino acid sequence of MR, or SEQ ID NO: 1 (KAKRFKKH), or SEQ ID NO: 2 (AHFWQQA), or SEQ ID NO: 3 (CDLPQTHSL), or SEQ ID NO: 4 (IEPD), or SEQ ID NO: 5 (IEPDSPGT), or SEQ ID NO: 6 (MCDLPQTHSL), or SEQ ID NO: 7 (AEAGITGTWYNQLGSTFIVTAGADGALTGTYESAVGNAESRYVLTGRYDSAPATDGSGTALGWTVAWKNNYRNAHSATTWSGQYVGGAEARINTQWLLTSGTTEANAWKSTLVGHDTFTKVKPSAAS), or SEQ ID NO: 8 (TDPEFQQQQQLLDVVKRQQELLRLTVWGTKNLQARVTAIEKYLQDQARLNSWGCAFRQVCHTTVPWVNDSLAPDWDNMTWQEWEKQVRYLEANISKSLEQAQIQQEKNMYELQKLNSWDIRSVV). In a further embodiment the leading amino acid sequence has the amino acid sequence selected from MR, or SEQ ID NO: 1 (KAKRFKKH), or SEQ ID NO: 2 (AHFWQQA), or SEQ ID NO: 3 (CDLPQTHSL), or SEQ ID NO: 4 (IEPD), or SEQ ID NO: 5 (IEPDSPGT), or SEQ ID NO: 6 (MCDLPQTHSL).
The term “amino acid sequence tag” denotes a sequence of amino acid residues connected to each other via peptide bonds that has specific binding properties. In one embodiment the amino acid sequence tag is an affinity or purification tag. In an embodiment the amino acid sequence tag is selected from Arg-tag, His-tag, Flag-tag, 3× Flag-tag, Strep-tag, Nano-tag, SBP-tag, c-myc-tag, S-tag, calmodulin-binding-peptide, cellulose-binding-domain, chitin-binding-domain, GST-tag, or MBP-tag. In a further embodiment the amino acid sequence tag is selected from SEQ ID NO: 9 (RRRRR) or SEQ ID NO: 10 (RRRRRR), or SEQ ID NO: 11 (HHHHHH), or SEQ ID NO: 12 (KDHLIHNVHKEFHAHAHNK) or SEQ ID NO: 13 (DYKDDDDK) or SEQ ID NO: 14 (DYKDHDGDYKDHDIDYKDDDDK) or SEQ ID NO: 15 (AWRHPQFGG) or SEQ ID NO: 16 (WSHPQFEK) or SEQ ID NO: 17 (MDVEAWLGAR) or SEQ ID NO: 18 (MDVEAWLGARVPLVET) or SEQ ID NO: 19 (MDEKTTGWRGGHVVEGLAGELEQLRARLEHHPQGQREP) or SEQ ID NO: 20 (EQKLISEEDL) or SEQ ID NO: 21 (KETAAAKFERQHMDS) or SEQ ID NO: 22 (KRRWKKNFIAVSAANRFKKISSSGAL) or SEQ ID NO: 23 (cellulose binding domain) or SEQ ID NO: 24 (cellulose binding domain) or SEQ ID NO: 25 (TNPGVSAWQVNTAYTAGQLVTYNGKTYKCLQPHTSLAGWEPSNVPALWQLQ) or SEQ ID NO: 26 (GST-tag) or SEQ ID NO: 27 (MBP-tag).
The term “enzymatic cleavage site” denotes a sequence of amino acid residues connected to each other via peptides bonds that can specifically be cleaved by a protease. In one embodiment the protease is IgA-protease, Granzyme B, Tev protease, Prescission protease, Thrombin, Factor Xa, or Enterokinase.
The term “IgA-protease” denotes a protease derived from Neisseria gonorrhoeae with a recognition site comprising one of the following sequences wherein “↓” denotes the position of the cleaved bond:









(SEQ ID NO: 28)



Pro-Ala-Pro ↓ Ser-Pro,



 



(SEQ ID NO: 29)



Pro-Pro ↓ Ser-Pro,



 



(SEQ ID NO: 30)



Pro-Pro ↓ Ala-Pro,



 



(SEQ ID NO: 31)



Pro-Pro ↓ Thr-Pro,



 



(SEQ ID NO: 32)



Pro-Pro ↓ Gly-Pro,



 



(SEQ ID NO: 33)



Pro-Arg-Pro-Pro ↓ Thr-Pro,



 



(SEQ ID NO: 34)



Val-Val-Ala-Pro-Pro ↓ Ala-Pro,



 



(SEQ ID NO: 35)



Val-Val-Ala-Pro-Pro ↓ Ser-Pro



 



(SEQ ID NO: 36)



Val-Val-Ala-Pro-Pro ↓ Thr-Pro



 



(SEQ ID NO: 37)



Val-Val-Ala-Pro-Pro ↓ Gly-Pro



 



(SEQ ID NO: 39)



Ala-Pro-Pro-Ala ↓ Ala-Pro,



 



(SEQ ID NO: 40)



Pro-Arg-Pro-Pro ↓ Ala-Pro.



 



(SEQ ID NO: 41)



Pro-Arg-Pro-Pro ↓ Ser-Pro



 



(SEQ ID NO: 42)



Pro-Arg-Pro-Pro ↓ Gly-Pro






The term “operably linked” denotes a juxtaposition of two or more components, wherein the components so described are in a relationship permitting them to function in their intended manner. For example, joining two polypeptide encoding regions such as a secretory leader and a polypeptide.
Linking of amino acid sequence encoding nucleic acid is accomplished by recombinant methods known in the art, e.g., using PCR methodology and/or by ligation at convenient restriction sites. If convenient restriction sites do not exist, then synthetic oligonucleotide adaptors or linkers are used in accord with conventional practice.
For the recombinant production of a polypeptide of interest in a prokaryotic cell among other things high expression yield and practicable down stream processing are envisaged.
A pro-polypeptide comprising in N- to C-terminal direction

    
    
        a first dipeptide GS,
        an amino acid sequence tag,
        a second dipeptide GS, and
        an enzymatic cleavage site

as reported herein is useful for the expression of an operably linked polypeptide of interest. The advantageous properties can be exerted when the pro-polypeptide as reported herein is fused to the N-terminus of a polypeptide of interest, which is intended to be expressed by recombinant means in a prokaryotic cell. Thus, the pro-polypeptide as reported herein can be used to improve expression yield and downstream processing. The polypeptide of interest is expressed by the prokaryotic cell as fusion polypeptide comprising the pro-polypeptide as reported herein and the polypeptide of interest. That is the fusion polypeptide comprises in N- to C-terminal direction the pro-polypeptides as reported herein and the polypeptide of interest.

    
    









TABLE 1







Expression yield of different fusion polypeptides. The first yield


value given in each cell was obtained with a fermentation method


according to Example 3b, the second yield value in each cell was


obtained with a fermentation method according to Example 3a.











elements of the N-terminal pro-polypeptide of the fusion






polypeptide




















leading

amino



molecular





amino

acid

intervening
enzymatic
weight of


SEQ


acid
dipep-
sequence
dipep-
amino acid
cleavage
the fusion

yield
ID


sequence
tide
tag
tide
sequence
site
polypeptide
yield
[10−3
NO:



















MR
GS
HHHHHH_
GS
n.p.
PRPPTP_
34904.1
24.3
0.696
79




(SEQ ID


(SEQ ID

12.8
0.367





NO: 11)


NO: 33)






MCDLP
GS
HHHHHH
GS
n.p.
VVAPPAP.
35472.7
20.3
0.572
80


QTHSL_

(SEQ ID


(SEQ ID

10.5
0.296



(SEQ ID

NO: 11)


NO: 34)






NO: 6)











MR
GS
HHHHHH
GS
AEAGITGTWYNQL
VVAPPAP.
48373.5
7.9
0.163
81




(SEQ ID

GSTFIVTAGADGA
(SEQ ID

3.5
0.072





NO: 11)

LTGTYESAVGNAE
NO: 34)










SRYVLTGRYDSAP











ATDGSGTALGWTV











AWKNNYRNAHSAT











TWSGQYVGGAEAR











INTQWLLTSGTTE











ANAWKSTLVGHDT











FTKVKPSAAS_











(SEQ ID NO:











34)







MR
GS
HHHHHH_
n.p.
AHFWQQA_
PRPPTP_
35372.5
9.0
0.254
82




(SEQ ID

(SEQ ID
(SEQ ID

2.4
0.068





NO: 11)

NO: 2)
NO: 38)






MR
GS
HHHHHH_
n.p.
TDPEFQQQQQLLD
APPAAP_
49653.5
10.2
0.205
85




(SEQ ID

VVKRQQELLRLTV
(SEQ ID

7.0
0.141





NO: 11)

WGTKNLQARVTAI
NO: 39)










EKYLQDQARLNSW











GCAFRQVCHTTVP











WVNDSLAPDWDNM











TWQEWEKQVRYLE











ANISKSLEQAQIQ











QEKNMYELQKLNS











WDIRSVV_











(SEQ ID











NO: 8)







M
n.p.
HHHHHH_
n.p.
KAKRFKKH
PRPPAP_
35453.9
11.1
0.313
84




(SEQ ID

(SEQ ID
(SEQ ID

2.6
0.073





NO: 11)

NO: 1)
NO: 40)





n.p. = not present






From Table 1 it can be seen that fusion polypeptides comprising the pro-polypeptide as reported herein at the N-terminus in which between the second dipeptides GS and the enzymatic cleavage site no additional amino acid sequence is inserted provide for higher expression yield than those comprising an intervening amino acid sequence. A leading amino acid sequence of two or more amino acid residues may be present N-terminal to the first dipeptide GS.
At its C-terminus the pro-polypeptide as reported herein contains an enzymatic cleavage site. The enzymatic cleavage site is an amino acid sequence that contains a recognition motif for a protease. This recognition site can be for any protease as long as the protease cleaves specifically at this recognition site, i.e. this sequence occurs only once in the entire amino acid sequence of the fusion polypeptide.
Especially advantageous is the possibility for endotoxin removal while the fusion polypeptide is bound to an affinity chromatography material, i.e. to an affinity material that has not specifically been designed for the polypeptide of interest but for the amino acid sequence tag. With these binding properties any corresponding combination of amino acid sequence tag and corresponding affinity material can be used. After the endotoxin removal the polypeptide of interest can efficiently be recovered from the fusion polypeptide by using the protease cleavage site.
The following examples are provided to aid the understanding of the present invention, the true scope of which is set forth in the appended claims. It is understood that modifications can be made in the procedures set forth without departing from the spirit of the invention.
EXAMPLES
Materials & Methods
Recombinant DNA Techniques
Standard methods were used to manipulate DNA as described in Sambrook, J., et al., Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory Press, 2nd edition, New York, (December 1989). The molecular biological reagents were used according to the manufacturer's instructions.
Gene Synthesis
Desired gene segments were prepared from oligonucleotides made by chemical synthesis. The gene segments, which are flanked by singular restriction endonuclease cleavage sites, were assembled by annealing and ligation of oligonucleotides including PCR amplification and subsequently cloned into the pCR2.1-TOPO-TA cloning vector (Invitrogen Corp., USA) via A-overhangs. The DNA sequence of the subcloned gene fragments were confirmed by DNA sequencing.
Example 1
Making and Description of the E. coli Expression Plasmids
The tetranectin-apolipoprotein A1 fusion polypeptide was prepared by recombinant means. The amino acid sequence of three different tetranectin-apolipoprotein A1 fusion polypeptides is given below (bold, tetranectin-trimerization domain, variant A and B). Variant A differs from variant B by the addition of two amino acid residues at the N-terminus of the tetranectin domain. Variant C differs from variant A by the addition of five amino acid residues at the C-terminal end of the tetranectin domain.








Amino acid sequence of Variant A (SEQ ID NO: 44):










  1
IVNAKKDVVN TKMFEELKSR LDTLAQEVAL LKEQQALQTV DEPPQSPWDR



 


 51
VKDLATVYVD VLKDSGRDYV SQFEGSALGK QLNLKLLDNW DSVTSTFSKL


 


101
REQLGPVTQE FWDNLEKETE GLRQEMSKDL EEVKAKVQPY LDDFQKKWQE


 


151
EMELYRQKVE PLRAELQEGA RQKLHELQEK LSPLGEEMRD RARAHVDALR


 


201
THLAPYSDEL RQRLAARLEA LKENGGARLA EYHAKATEHL STLSEKAKPA


 


251
LEDLRQGLLP VLESFKVSFL SALEEYTKKL NTQ


 








Amino acid sequence of Variant B (SEQ ID NO: 77):










  1
KKIVNAKKD VVNTKMFEEL KSRLDTLAQE VALLKEQQAL QTVDEPPQSP



 


 51
WDRVKDLATV YVDVLKDSGR DYVSQFEGSA LGKQLNLKLL DNWDSVTSTF


 


101
SKLREQLGPV TQEFWDNLEK ETEGLRQEMS KDLEEVKAKV QPYLDDFQKK


 


151
WQEEMELYRQ KVEPLRAELQ EGARQKLHEL QEKLSPLGEE MRDRARAHVD


 


201
ALRTHLAPYS DELRQRLAAR LEALKENGGA RLAEYHAKAT EHLSTLSEKA


 


251
KPALEDLRQG LLPVLESFKV SFLSALEEYT KKLNTQ


 








Amino acid sequence of Variant C (SEQ ID NO: 78):










  1
IVNAKKDVVN TKMFEELKSR LDTLAQEVAL LKEQQALQTV SLKGTDEPPQ



 


 51
SPWDRVKDLA TVYVDVLKDS GRDYVSQFEG SALGKQLNLK LLDNWDSVTS


 


101
TFSKLREQLG PVTQEFWDNL EKETEGLRQE MSKDLEEVKA KVQPYLDDFQ


 


151
KKWQEEMELY RQKVEPLRAE LQEGARQKLH ELQEKLSPLG EEMRDRARAH


 


201
VDALRTHLAP YSDELRQRLA ARLEALKENG GARLAEYHAK ATEHLSTLSE


 


251
KAKPALEDLR QGLLPVLESF KVSFLSALEE YTKKLNTQ






The tetranectin-apolipoprotein A1 fusion polypeptides were expressed as precursor polypeptides (larger fusion polypeptides) in E. coli. The following N-terminal pro-polypeptides were tested for improved expression yield and downstream processing:

    
    
        1) Amino acid sequence of pro-polypeptide combined with variant B (plasmid 5803):
    
    











(SEQ ID NO: 79)



MRGSHHHHHH GSPRPPTP






    
    
        
        
            Pro-polypeptide 5803 is an artificial polypeptide comprising in N- to C-terminal direction:
            
                a leading amino acid sequence that has the amino acid sequence MR,
                a first dipeptide GS,
                a hexa-histidine tag that has the amino acid sequence of HHHHHH (SEQ ID NO: 11),
                a second dipeptide GS, and
                an IgA protease cleavage site that has the amino acid sequence of PRPPTP (SEQ ID NO: 33).
            
            
        
        
        2) Amino acid sequence of pro-polypeptide combined with variant A (plasmid 5816):
    
    









(SEQ ID NO: 80)


MCDLPQTHSL GSHHHHHHGS VVAPPAP






    
    
        
        
            Pro-polypeptide 5816 is an artificial polypeptide comprising in N- to C-terminal direction:
            
                a leading amino acid sequence encoding a methionine conjugated to a fragment of an interferon sequence with the amino acid sequence of MCDLPQTHSL (SEQ ID NO: 06),
                a first dipeptide GS,
                a hexa-histidine tag that has the amino acid sequence of HHHHHH (SEQ ID NO: 11),
                a second dipeptide GS, and
                an IgA protease cleavage site that has the amino acid sequence of VVAPPAP (SEQ ID NO: 34)
            
            
        
        
        3) Amino acid sequence of pro-polypeptide combined with variant A (plasmid 5820):
    
    










(SEQ ID NO: 81)










  1
MRGSHHHHHH GSAEAGITGT WYNQLGSTFI VTAGADGALT GTYESAVGNA



 


 51
ESRYVLTGRY DSAPATDGSG TALGWTVAWK NNYRNAHSAT TWSGQYVGGA


 


101
EARINTQWLL TSGTTEANAW KSTLVGHDTF TKVKPSAASV VAPPAP






    
    
        
        
            Pro-polypeptide 5820 is an artificial polypeptide comprising in N- to C-terminal direction:
            
                a leading amino acid sequence that has the amino acid sequence MR,
                a first dipeptide GS,
                a hexa-histidine tag that has the amino acid sequence of HHHHHH (SEQ ID NO: 11),
                a second dipeptide GS,
                an intervening amino acid sequence derived from streptavidin, and
                an IgA protease cleavage site that has the amino acid sequence of VVAPPAP (SEQ ID NO: 34)
            
            
        
        
        4) Amino acid sequence of pro-polypeptide combined with variant A (plasmid 5805):
    
    









(SEQ ID NO: 82)


MRGSHHHHHH AHFWQQAPRP PTP






    
    
        
        
            Pro-polypeptide 5805 is an artificial polypeptide comprising in N- to C-terminal direction:
            
                a leading amino acid sequence that has the amino acid sequence MR,
                a first dipeptide GS,
                a hexa-histidine tag that has the amino acid sequence of HHHHHH (SEQ ID NO: 11),
                an intervening amino acid sequence that has the amino acid sequence AHFWQQA (SEQ ID NO: 02), and
                an IgA protease cleavage site that has the amino acid sequence of PRPPTP (SEQ ID NO: 38)
            
            
        
        
        5) Amino acid sequence of pro-polypeptide combined with variant C (plasmid 5819):
    
    










(SEQ ID NO: 83)










1
MRGSHHHHHH TDPEFQQQQQ LLDVVKRQQE LLRLTVWGTK NLQARVTAIE



 


51
KYLQDQARLN SWGCAFRQVC HTTVPWVNDS LAPDWDNMTW QEWEKQVRYL


 


101
EANISKSLEQ AQIQQEKNMY ELQKLNSWDI RSVVAPPAP






    
    
        
        
            Pro-polypeptide 5819 is an artificial polypeptide comprising in N- to C-terminal direction:
            
                a leading amino acid sequence that has the amino acid sequence MR,
                a first dipeptide GS,
                a hexa-histidine tag that has the amino acid sequence of HHHHHH (SEQ ID NO: 11),
                an intervening amino acid sequence derived from the human HIV2 gp32 protein, and
                an IgA protease cleavage site that has the amino acid sequence of VVAPPAP (SEQ ID NO: 34)
            
            
        
        
        6) Amino acid sequence of pro-polypeptide combined with variant B (plasmid 5806):
    
    









(SEQ ID NO: 84)


MHHHHHHKAK RFKKHPRPPAP






    
    
        
        
            Pro-polypeptide 5806 is an artificial polypeptide comprising in N- to C-terminal direction:
            
                a leading amino acid sequence (M, start codon),
                a hexa-histidine tag that has the amino acid sequence of HHHHHH (SEQ ID NO: 11),
                an intervening amino acid sequence that has the amino acid sequence of KAKRFKKH (SEQ ID NO: 01), and
                an IgA protease cleavage site that has the amino acid sequence of PRPPAP (SEQ ID NO: 40)
            
            
        
        
    
    


The tetranectin-apolipoprotein A1 variant polypeptides were recovered from the fusion precursor protein by enzymatic cleavage in vitro using IgA protease.
The different pro-polypeptide tetranectin-apolipoprotein A1 encoding fusion genes, designated 5803, 5816, 5820, 5805, 5819 and 5806, were assembled with known recombinant methods and techniques by connection of appropriate nucleic acid segments. Nucleic acid sequences made by chemical synthesis were verified by DNA sequencing.
Making and Description of the Basic/Starting E. Coli Expression Plasmid 4980
Plasmid 4980 (4980-pBRori-URA3-LACI-SAC) is an expression plasmid for the expression of core-streptavidin in E. coli. It was generated by ligation of the 3142 bp long EcoRI/CelII-fragment derived from plasmid 1966 (1966-pBRori-URA3-LACI-T-repeat; reported in EP-B 1 422 237) with the 435 bp long core-streptavidin encoding EcoRI/CelII-fragment.
The core-streptavidin E. coli expression plasmid comprises the following elements:

    
    
        the origin of replication from the vector pBR322 for replication in E. coli (corresponding to by position 2517-3160 according to Sutcliffe, J. G., et al., Quant. Biol. 43 (1979) 77-90),
        the URA3 gene of Saccharomyces cerevisiae coding for orotidine 5′-phosphate decarboxylase (Rose, M., et al., Gene 29 (1984) 113-124) which allows plasmid selection by complementation of E. coli pyrF mutant strains (uracil auxotrophy),
        the core-streptavidin expression cassette built up of
        
            the T5 hybrid promoter (T5-PN25/03/04 hybrid promoter according to Bujard, H., et al., Methods. Enzymol. 155 (1987) 416-433 and Stueber, D., et al., Immunol. Methods IV (1990) 121-152) including a synthetic ribosomal binding site according to Stüber, D., et al., (see before),
            the core-streptavidin gene, and
            two bacteriophage-derived transcription terminators, the λ-T0 terminator (Schwarz, E., et al., Nature 272 (1978) 410-414) and the fd-terminator (Beck, E., and Zink, B., Gene 1-3 (1981) 35-58), and
        
        
        the lacI repressor gene from E. coli (Farabaugh, P. J., Nature 274 (1978) 765-769).

Making of the Final Expression Plasmids Comprising Pro-Polypeptides (Plasmids 5803, 5816, 5820, 5805, 5819 and 5806)

    
    


Plasmid 5803 (5803-His6-IgA-TP7-TripB-ApoAI) (“His6” disclosed as SEO ID NO: 11) is the plasmid for the expression of the tetranectin-apolipoprotein A1 precursor protein containing pro-polypeptide 5803. It was prepared by excising the core-streptavidin structural gene from vector 4980 using the singular flanking EcoRI and CelII restriction endonuclease cleavage site and insertion of the 958 bp long EcoRII/CelII 5803 pro-polypeptide tetranectin-apolipoprotein A1 precursor protein encoding gene segment into the 3142 bp long EcoRI/CelII-4980 vector fragment.
Plasmids (“his6” Disclosed as SEQ ID NO: 11 in the Following):


    
    
        5816 (5816-IFN-His6-IgA-API10-TripB-ApoAI),
        5820 (5820-His6-coreSA-IgA-API10-TripB-ApoA1),
        5805 (5805-His6-IgA-Pro-TPI10-TripB-ApoAI),
        5819 (5819-gp32-His6-IgA-API10-TriB-SLKGT-ApoA1), and
        5806 (5806-His6-IgA-Opt-AP7-TripB-ApoAI)

were generated as described before for plasmid 5803.

    
    


Example 2
Expression of the Tetranectin-Apolipoprotein A1 Precursor Protein from Plasmids 5803, 5816, 5820, 5805, 5819 and 5806 in E. coli 
For the expression of the tetranectin-apolipoprotein A1 precursor proteins 5803, 5816, 5820, 5805, 5819 and 5806 an E. coli host/vector system was employed which enables an antibiotic-free plasmid selection by complementation of an E. coli auxotrophy (PyrF) (see e.g. EP-B 0 972 838 and U.S. Pat. No. 6,291,245).
The tetranectin-apolipoprotein A1 precursor proteins were expressed in the E. coli strain CSPZ-2 (leuB, proC, trpE, thi-1, ΔpyrF).
Transformation and Cell Culturing by Complementation of a pyrF Auxotrophy in Selective Medium
The E. coli K12 strain CSPZ-2 (leuB, proC, trpE, thi-1, ΔpyrF) was transformed with the expression plasmids (5803, 5816, 5820, 5805, 5819 and 5806, respectively) obtained in previous step. The transformed CSPZ-2 cells were first grown at 37° C. on agar plates and subsequently in a shaking culture in M9 minimal medium containing 0.5% casamino acids (Difco) up to an optical density at 550 nm (OD550) of 0.6-0.9 and subsequently induced with IPTG (1-5 mmol/l final concentration).
After an induction phase of 4 to 16 hours at 37° C. the cytoplasmic and soluble expressed tetranectin-apolipoprotein A1 precursor proteins were transferred to insoluble protein aggregates, the so called inclusion bodies, with a heat step where the whole culture broths in the Erlenmeyer flasks were heated to 50° C. for 1 or 2 hours before harvest (see e.g. EP-B 1 486 571). Thereafter, the cells were harvested by centrifugation, washed with 50 mmol/l potassium phosphate buffer, pH 6.5, and stored at −20° C. until further processing.
Expression Analysis
For expression analysis cell pellets from 3 OD550 nm units (1 OD550 nm=1 ml cell suspension with an OD at 550 nm of 1) of centrifuged culture medium were resuspended in 0.25 ml 10 mmol/l potassium phosphate buffer, pH 6.5, and the cells were lysed by ultrasonic treatment (two pulses of 30 sec. at 50% intensity). The insoluble cell components were sedimented (centrifugation 14,000 rpm, 5 min.) and the supernatant was admixed with 1⁄5 of its volume 5×SDS sample buffer (1×SDS sample buffer: 50 mmol/l Tris-HCl, pH 6.8, 1% SDS, 50 mmol/l DTT, 10% glycerol, 0.001% bromophenol blue). The insoluble cell debris fraction (pellet) was resuspended in 0.3 ml 1×SDS sample buffer, the samples were incubated for 5 min. at 95° C. and centrifuged again. Subsequently, the proteins were separated by SDS polyacrylamide gel electrophoresis (PAGE) (Laemmli, U.K., Nature 227 (1970) 680-685) and stained with Coomassie Brilliant Blue R dye.
The synthesized tetranectin-apolipoprotein A1 precursor proteins were homogeneous and found in the insoluble cell debris fraction in the form of insoluble protein aggregates (IBs). The expression yield was comparable within the scope of the measurement accuracy in all clones and was between 30-60% relative to the total E. coli protein.
Example 3
10 l High Cell Density Fermentations of E. coli for the Recombinant Production of the Tetranectin-Apolipoprotein A1 Precursor Proteins
Example 3a
Pre-Culture
For pre-fermentation a M9 medium according to Sambrook, J., et al., (Molecular Cloning: A Laboratory Manual; Cold Spring Harbor Laboratory Press; 2nd edition, New York, (December 1989)) supplemented with about 1 g/l L-leucine, about 1 g/l L-proline and about 1 mg/l thiamine-HCl has been used.
For pre-fermentation 300 ml of M9-medium in a 1000 ml Erlenmeyer-flask with baffles was inoculated with 2 ml out of a primary seed bank ampoule. The cultivation was performed on a rotary shaker for 13 hours at 37° C. until an optical density (578 nm) of 1-3 was obtained.
10 l Fed-Batch Main Fermentation
For fermentation a batch medium according to Riesenberg, et al., was used (Riesenberg, D., et al., J. Biotechnol. 20 (1991) 17-27): 27.6 g/l glucose*H2O, 13.3 g/l KH2PO4, 4.0 g/l (NH4)2HPO4, 1.7 g/l citrate, 1.2 g/l MgSO4*7 H2O, 60 mg/l iron(III)citrate, 2.5 mg/l CoCl2*6 H2O, 15 mg/l MnCl2*4 H2O, 1.5 mg/l CuCl2*2 H2O, 3 mg/l H3BO3, 2.5 mg/l Na2MoO4*2 H2O, 8 mg/l Zn(CH3COO)2*2 H2O, 8.4 mg/l TITRIPLEX IIITM, 1.3 ml/l SYNPERONICTM 10% anti foam agent. The batch medium was supplemented with 5.4 mg/l Thiamin-HCl and 1.2 g/l L-leucine and L-proline respectively. The feed 1 solution contained 700 g/l glucose supplemented with 19.7 g/l MgSO4*7 H2O. The alkaline solution for pH regulation was an aqueous 12.5% (w/v) NH3 solution supplemented with 50 g/l L-leucine and 50 g/l L-proline respectively. All components were dissolved in deionized water.
The fermentation was carried out in a 10 l BIOSTATTM C DCU3 fermenter (Sartorius, Melsungen, Germany). Starting with 6.4 l sterile fermentation batch medium plus 300 ml inoculum from the pre-fermentation the batch fermentation was performed at 37° C., pH 6.9±0.2, 500 mbar and an aeration rate of 10 l/min. After the initially supplemented glucose was depleted the temperature was shifted to 28° C. and the fermentation entered the fed-batch mode. Here the relative value of dissolved oxygen (pO2) was kept at 50% (DO-stat, see e.g. Shay, L. K., et al., J. Indus. Microbiol. (1987) 79-85) by adding feed 1 in combination with constantly increasing stirrer speed (550 rpm to 1000 rpm within 10 hours and from 1000 rpm to 1400 rpm within 16 hours) and aeration rate (from 10 l/min to 16 l/min in 10 hours and from 16 l/min to 20 l/min in 5 hours). The supply with additional amino acids resulted from the addition of the alkaline solution, when the pH reached the lower regulation limit (6.70) after approximately 8 hours of cultivation. The expression of recombinant therapeutic protein was induced by the addition of 1 mM IPTG at an optical density of 70.
Harvesting the Biomass
At the end of fermentation the cytoplasmatic and soluble expressed tetranectin-apolipoprotein A1 is transferred to insoluble protein aggregates, the so called inclusion bodies, with a heat step where the whole culture broth in the fermenter is heated to 50° C. for 1 or 2 hours before harvest (see e.g. EP-B 1 486 571). Thereafter, the content of the fermenter was centrifuged with a flow-through centrifuge (13,000 rpm, 13 l/h) and the harvested biomass was stored at −20° C. until further processing. The synthesized tetranectin-apolipoprotein A1 precursor proteins were found exclusively in the insoluble cell debris fraction in the form of insoluble protein aggregates, so-called inclusion bodies (IBs).
Product Quantification
Samples drawn from the fermenter, one prior to induction and the others at dedicated time points after induction of protein expression are analyzed with SDS-Polyacrylamide gel electrophoresis. From every sample the same amount of cells (ODTarget=5) are resuspended in 5 mL PBS buffer and disrupted via sonication on ice. Then 100 μL of each suspension are centrifuged (15,000 rpm, 5 minutes) and each supernatant is withdrawn and transferred to a separate vial. This is to discriminate between soluble and insoluble expressed target protein. To each supernatant (=soluble) fraction 300 μL and to each pellet (=insoluble) fraction 400 μL of SDS sample buffer (Laemmli, U.K., Nature 227 (1970) 680-685) are added. Samples are heated for 15 minutes at 95° C. under shaking to solubilize and reduce all proteins in the samples. After cooling to room temperature 5 μL of each sample are transferred to a 4-20% TGX CRITERIONTM Stain Free polyacrylamide gel (Bio-Rad). Additionally 5 μl molecular weight standard (PRECISION PLUSTM Protein Standard, Bio-Rad) and 3 amounts (0.3 μl, 0.6 μl and 0.9 μl) quantification standard with known product protein concentration (0.1 μg/μl) are positioned on the gel.
The electrophoresis was run for 60 Minutes at 200 V and thereafter the gel was transferred the GELDOC EZTM Imager (Bio-Rad) and processed for 5 minutes with UV radiation. Gel images were analyzed using IMAGE LABTM analysis software (Bio-Rad). With the three standards a linear regression curve was calculated with a coefficient of >0.99 and thereof the concentrations of target protein in the original sample was calculated.
Example 3b
Pre-Culture
For pre-fermentation a M9 medium according to Sambrook et al. (Molecular Cloning: A laboratory manual. Cold Spring Harbor Laboratory Press; 2nd edition (December 1989)) supplemented with about 1 g/l L-leucine, about 1 g/l L-proline and about 1 mg/l thiamine-HCl has been used.
For pre-fermentation 300 ml of modified M9-medium in a 1000 ml Erlenmeyer-flask with baffles was inoculated from agar plate or with 1-2 ml out of a primary seed bank ampoule. The cultivation was performed on a rotary shaker for 13 hours at 37° C. until an optical density (578 nm) of 1-3 was obtained.
10 l Fed-Batch Main Fermentation
For fermentation and high yield expression of tetranectin-apolipoprotein A1 the following batch medium and feeds were used (Schantz, previously unpublished):
8.85 g/l glucose, 63.5 g/l yeast extract, 2.2 g/l NH4Cl, 1.94 g/l L-leucine, 2.91 g/l L-proline, 0.74 g/l L-methionine, 17.3 g/l KH2PO4*H2O, 2.02 g/l MgSO4*7 H2O, 25.8 mg/l Thiamin-HCl, 1.0 ml/l SYNPERONICTM 10% anti foam agent. The feed 1 solution contained 333 g/l yeast extract and 333 g/l 85%-glycerol supplemented with 1.67 g/l L-methionine and 5 g/l L-leucine and L-proline each. The feed 2 was a solution of 600 g/l L-Proline. The alkaline solution for pH regulation was a 10% (w/v) KOH solution and as acid a 75% glucose solution was used. All components were dissolved in deionized water.
The fermentation was carried out in a 10 l BIOSTATTM C DCU3 fermenter (Sartorius, Melsungen, Germany). Starting with 5.15 l sterile fermentation batch medium plus 300 ml inoculum from the pre-fermentation the fed-batch fermentation was performed at 25° C., pH 6.7±0.2, 300 mbar and an aeration rate of 10 l/min. Before the initially supplemented glucose was depleted the culture reached an optical density of 15 (578 nm) and the fermentation entered the fed-batch mode when feed 1 was started with 70 g/h. Monitoring the glucose concentration in the culture the feed 1 was increased to a maximum of 150 g/h while avoiding glucose accumulation and keeping the pH near the upper regulation limit of 6.9. At an optical density of 50 (578 nm) feed 2 was started with a constant feed rate of 10 ml/h. The relative value of dissolved oxygen (pO2) was kept above 50% by increasing stirrer speed (500 rpm to 1500 rpm), aeration rate (from 10 l/min to 20 l/min) and pressure (from 300 mbar to 500 mbar) in parallel. The expression of recombinant therapeutic protein was induced by the addition of 1 mM IPTG at an optical density of 90.
Product Quantification
Seven samples drawn from the fermenter, one prior to induction and the others at dedicated time points after induction of protein expression are analyzed with SDS-Polyacrylamide gel electrophoresis. From every sample the same amount of cells (ODTarget=5) are resuspended in 5 mL PBS buffer and disrupted via sonication on ice. Then 100 μL of each suspension are centrifuged (15,000 rpm, 5 minutes) and each supernatant is withdrawn and transferred to a separate vial. This is to discriminate between soluble and insoluble expressed target protein. To each supernatant (=soluble) fraction 300 μL and to each pellet (=insoluble) fraction 200 μL of SDS sample buffer (Laemmli, U.K., Nature 227 (1970) 680-685) are added. Samples are heated for 15 minutes at 95° C. under shaking to solubilize and reduce all proteins in the samples. After cooling to room temperature 5 μL of each sample are transferred to a 10% Bis-Tris polyacrylamide gel (Novagen). Additionally 5 μl molecular weight standard (PRECISION PLUSTM Protein Standard, Bio-Rad) and 3 amounts (0.3 μl, 0.6 μl and 0.9 μl) quantification standard with known product protein concentration (0.1 μg/μl) are positioned on the gel.
The electrophoresis was run for 35 minutes at 200 V and then the gel was stained with Coomassie Brilliant Blue R dye, destained with heated water and transferred to an optical densitometer for digitalization (GS710, Bio-Rad). Gel images were analyzed using QUANTITY ONETM 1-D analysis software (Bio-Rad). With the three standards a linear regression curve is calculated with a coefficient of >0.98 and thereof the concentrations of target protein in the original sample was calculated.
Harvesting the Biomass
At the end of fermentation the cytoplasmatic and soluble expressed tetranectin-apolipoprotein A1 is transferred to insoluble protein aggregates, the so called inclusion bodies (IBs), with a heat step where the whole culture broth in the fermenter is heated to 50° C. for 1 or 2 hours before harvest (see e.g. EP-B 1 486 571). After the heat step the synthesized tetranectin-apolipoprotein A1 precursor proteins were found exclusively in the insoluble cell debris fraction in the form of IBs.
The contents of the fermenter are cooled to 4-8° C., centrifuged with a flow-through centrifuge (13,000 rpm, 13 l/h) and the harvested biomass is stored at −20° C. until further processing. The total harvested biomass yield ranged between 39 g/l and 90 g/l dry matter depending on the expressed construct.

## Claims

1. A fusion polypeptide comprising in N- to C-terminal direction:
a leading amino acid sequence of SEQ ID NO. 06;
a first dipeptide GS;
an amino acid sequence tag having the amino acid sequence of SEQ ID NO. 11;
a second dipeptide GS adjacent thereto;
an enzymatic cleavage site having the amino acid sequence of SEQ ID NO. 34; and
a polypeptide of interest having the amino acid sequence of SEQ ID NO. 43, SEQ ID NO. 44 or SEQ ID NO. 45.

2. The fusion polypeptide according to claim 1, wherein the amino acid at the N-terminus of the fusion polypeptide has a free alpha-amino group.

3. The fusion polypeptide of claim 1, wherein said polypeptide of interest has the amino acid sequence of SEQ ID NO. 43.

4. The fusion polypeptide of claim 1, wherein said polypeptide of interest has the amino acid sequence of SEQ ID NO. 44.

5. The fusion polypeptide of claim 1, wherein said polypeptide of interest has the amino acid sequence of SEQ ID NO. 45.

6. A fusion polypeptide comprising in N- to C-terminal direction:
a pro-peptide having the amino acid sequence of SEQ ID NO. 80; and
a polypeptide of interest having the amino acid sequence of SEQ ID NO. 43, SEQ ID NO. 44 or SEQ ID NO. 45.

7. The fusion polypeptide of claim 6, wherein said polypeptide of interest has the amino acid sequence of SEQ ID NO. 43.

8. The fusion polypeptide of claim 6, wherein said polypeptide of interest has the amino acid sequence of SEQ ID NO. 44.

9. The fusion polypeptide of claim 6, wherein said polypeptide of interest has the amino acid sequence of SEQ ID NO. 45.