Patent Application: US-4014108-A

Abstract:
human spasmolytic polypeptide which has the amino acid sequence glu lys pro ser pro cys gln cys ser arg leu ser pro his asn arg thr asn cys gly phe pro gly ile thr ser asp gln cys phe asp asn gly cys cys phe asp ser ser val thr gly val pro trp cys phe his pro leu pro lys gln glu ser asp gln cys val met glu val ser asp arg arg asn cys gly tyr pro gly ile ser pro glu glu cys ala ser arg lys cys cys phe ser asn phe ile phe glu val pro trp cys phe phe pro asn ser val glu asp cys his tyr or a functionally equivalent homologue thereof , characterized by being in glycosylated form .

Description:
it has been found that , at least when recombinant hsp is produced in yeast , the proportion of it that is provided in glycosylated form is in n - glycosylated form . it has further been found that glycosylation takes place at asn15 of the sequence shown above . in preferred embodiments of glycosylated hsp , the glycosylated side chain contains at least one hexose unit . in particular , the glycosylated side chain may contain at least one mannose unit , preferably at least five mannose units , most preferably at least ten mannose units . in one preferred embodiment of glycosylated hsp of the invention , the glycosylated side chain contains 13 - 17 mannose units . in other preferred embodiments , the glycosylated hsp is in addition glycosylated with at least one unit of n - acetyl glucosamine ( glcnac ). in the currently preferred embodiment , the glycosylated hsp is glycosylated at asn15 with ( glcnac ) 2 ( man ) 10 - 15 . it is further contemplated to produce homologues of hsp which are provided with one or more additional glycosylation sites . thus , the present invention also relates to hsp homologues , wherein lys2 is replaced by asn , gln7 is replaced by asn , arg10 is replaced by asn , gly 20 is replaced by thr or ser , gly23 is replaced by asn , ile 24 is replaced by asn , phe 36 is replaced by asn , asp 37 is replaced by asn , ser39 is replaced by asn , gln53 is replaced by asn , glu61 is replaced by asn , asp64 is replaced by asn , arg66 is replaced by thr or ser , gly69 is replaced by thr or ser , gly72 is replaced by asn , ile 89 is replaced by thr or ser , pro98 is replaced by asn or val101 is replaced by thr or ser , or a combination of two or more of these substitutions . in a currently preferred embodiment of such an hsp homologue , asp64 is replaced by asn , and arg66 is replaced by thr or ser . it is of course understood that hsp homologues of the invention may be glycosylated in the same manner at one or more of these sites as described above for glycosylation at asn15 . it is assumed that the trefoil structure common among spasmolytic polypeptides is important for the function of hsp and psp . the variant human or porcine sp comprising a fragment of the full - length polypeptide should therefore include at least three disulfide bonds to provide this structure . consequently , the variant may comprise at least a sequence of amino acids from position 8 to 46 or from position 58 to 95 , each of which sequences defines a trefoil domain of hsp and psp . as indicated above , the sp variant of the invention may be provided in non - glycosylated form . this may , for instance , be accomplished by substituting asn15 by another amino acid , e . g . asp or glu , or by substituting thr17 by another amino acid except ser , e . g . ala . it is more likely , however , that one or more additional glycosylation sites will be introduced into this domain , for instance by replacing arg10 by asn , gly 20 by thr or ser , gly23 by asn , ile 24 by asn , phe 36 by asn , asp 37 by asn , or ser39 by asn , or a combination of two or more of these substitutions . on the other hand , it may be desirable to provide the trefoil domain from position 58 to 95 with a glycosylation site lacking in this domain in native hsp and psp . thus , glu61 may be replaced by asn , asp64 by asn , arg66 by thr or ser , gly69 by thr or ser , or gly72 is replaced by asn , or a combination of two or more of these substitutions . in a currently preferred embodiment of the variant , asp64 is replaced by asn , and arg66 is replaced by thr or ser . it is of course understood that variants of the invention may be glycosylated in the same manner at one or more of these sites as described above for glycosylation at asn15 in full - length hsp . a dna sequence encoding hsp may suitably be isolated from a human genomic dna library by pcr ( polymerase chain reaction ) cloning using primers based on the published cdna sequence [ 8 ]. alternatively , the dna sequence may be prepared synthetically by established standard methods , e . g . the phosphoamidite method described by s . l . beaucage and m . h . caruthers , tetrahedron letters 22 , 1981 , pp . 1859 - 1869 , or the method described by matthes et al ., embo journal 3 , 1984 , pp . 801 - 805 . according to the phosphoamidite method , oligonucleotides are synthesized , e . g . in an automatic dna synthesizer , purified , annealed , ligated and cloned in suitable vectors . the cdna sequence shown in [ 8 ] may be used as the basis of oligonucleotide synthesis . alternatively , it is possible to use cdna coding for hsp obtained by screening a human cdna library with oligonucleotide probes in accordance with well - known procedures . furthermore , the dna sequence may be of mixed synthetic and genomic , mixed synthetic and cdna or mixed genomic and cdna origin prepared by ligating fragments of genomic , synthetic or cdna origin ( as appropriate ), the fragments corresponding to various parts of the entire dna sequence , in accordance with standard techniques . the sp variant of the invention may be encoded by a fragment of the full - length dna sequence , prepared by one of the methods indicated above , or by suitably truncating the full - length sequence . the dna sequence encoding hsp or an sp variant of the invention may then be inserted in a suitable expression vector . the recombinant expression vector may be any vector which may conveniently be subjected to recombinant dna procedures , and the choice of vector will often depend on the host cell into which it is to be introduced . thus , the vector may be an autonomously replicating vector , i . e . a vector which exists as an extrachromosomal entity , the replication of which is independent of chromosomal replication , e . g . a plasmid . alternatively , the vector may be one which , when introduced into a host cell , is integrated into the host cell genome and replicated together with the chromosome ( s ) into which it has been integrated . in the vector , the dna sequence encoding hsp or an sp variant of the invention should be operably connected to a suitable promoter sequence . the promoter may be any dna sequence which shows transcriptional activity in the host cell of choice and may be derived from genes encoding proteins either homologous or heterologous to the host cell . examples of suitable promoters for directing the transcription of the dna encoding the inhibitor of the invention in mammalian cells are the sv 40 promoter ( subramani et al ., mol . cell . biol . 1 , 1981 , pp . 854 - 864 ), the mt - 1 ( metallothionein gene ) promoter ( palmiter et al ., science 222 , 1983 , pp . 809 - 814 ) or the adenovirus 2 major late promoter . suitable promoters for use in yeast host cells include promoters from yeast glycolytic genes ( hitzeman et al ., j . biol . chem . 255 , 1980 , pp . 12073 - 12080 ; alber and kawasaki , j . mol . appl . gen . 1 , 1982 , pp . 419 - 434 ) or alcohol dehydrogenase genes ( young et al ., in genetic engineering of microorganisms for chemicals ( hollaender et al , eds . ), plenum press , new york , 1982 ), or the tpi1 ( u . s . pat . no . 4 , 599 , 311 ) or adh2 - 4 - c ( russell et al ., nature 304 , 1983 , pp . 652 - 654 ) promoters . suitable promoters for use in filamentous fungus host cells are , for instance , the adh3 promoter ( mcknight et al ., the embo j . 4 , 1985 , pp . 2093 - 2099 ) or the tpia promoter . the dna sequence encoding hsp or an sp variant may also be operably connected to a suitable terminator , such as the human growth hormone terminator ( palmiter et al ., op . cit .) or ( for fungal hosts ) the tpi1 ( alber and kawasaki , op . cit .) or adh3 ( mcknight et al ., op . cit .) promoters . the vector may further comprise elements such as polyadenylation signals ( e . g . from sv 40 or the adenovirus 5 elb region ), transcriptional enhancer sequences ( e . g . the sv 40 enhancer ) and translational enhancer sequences ( e . g . the ones encoding adenovirus va rnas ). the recombinant expression vector may further comprise a dna sequence enabling the vector to replicate in the host cell in question . an examples of such a sequence ( when the host cell is a mammalian cell ) is the sv 40 origin of replication , or ( when the host cell is a yeast cell ) the yeast plasmid 2μ replication genes rep 1 - 3 and origin of replication . the vector may also comprise a selectable marker , e . g . a gene the product of which complements a defect in the host cell , such as the gene coding for dihydrofolate reductase ( dhfr ) or one which confers resistance to a drug , e . g . neomycin , hygromycin or methotrexate , or the schizosaccharomyces pombe tpi gene ( described by p . r . russell , gene 40 , 1985 , pp . 125 - 130 . the procedures used to ligate the dna sequences coding for hsp or the sp variant , the promoter and the terminator , respectively , and to insert them into suitable vectors containing the information necessary for replication , are well known to persons skilled in the art ( cf ., for instance , sambrook et al ., molecular cloning : a laboratory manual , cold spring harbor , n . y ., 1989 ). the host cell into which the expression vector is introduced may be any cell which is capable of producing the inhibitor of the invention and is preferably a eukaryotic cell , such as a mammalian , yeast or fungal cell . the yeast organism used as the host cell may be any yeast organism which , on cultivation , produces large quantities of the inhibitor of the invention . examples of suitable yeast organisms are strains of the yeast species saccharomyces cerevisiae , saccharomyces kluyveri , schizosaccharomyces pombe or saccharomyces uvarum . the transformation of yeast cells may for instance be effected by protoplast formation followed by transformation in a manner known per se . examples of suitable mammalian cell lines are the cos ( atcc crl 1650 ), bhk ( atcc crl 1632 , atcc ccl 10 ) or cho ( atcc ccl 61 ) cell lines . methods of transfecting mammalian cells and expressing dna sequences introduced in the cells are described in e . g . kaufman and sharp , j . mol . biol . 159 , 1982 , pp . 601 - 621 ; southern and berg , j . mol . appl . genet . 1 , 1982 , pp . 327 - 341 ; loyter et al ., proc . natl . acad . sci . usa 79 , 1982 , pp . 422 - 426 ; wigler et al ., cell 14 , 1978 , p . 725 ; corsaro and pearson , somatic cell genetics 7 , 1981 , p . 603 , graham and van der eb , virology 52 , 1973 , p . 456 ; and neumann et al ., embo j . 1 , 1982 , pp . 841 - 845 . alternatively , fungal cells may be used as host cells . examples of suitable fungal cells are cells of filamentous fungi , e . g . aspergillus spp . or neurospora spp ., in particular strains of aspergillus oryzae or aspergillus niger . the use of aspergillus spp . for the expression of proteins is described in , e . g ., ep 238 023 . according to the present method , yeast cells are currently preferred for producing hsp and other sps ( such as those shown in fig1 ), as they have surprisingly been found to produce sp in a high yield and in at least 60 % glycosylated form . for instance , about two thirds of the hsp produced by yeast may be recovered in glycosylated form . the medium used to cultivate the cells may be any conventional medium suitable for growing mammalian cells or fungal ( including yeast ) cells , depending on the choice of host cell . the spasmolytic polypeptide will be secreted by the host cells to the growth medium and may be recovered therefrom by conventional procedures including separating the cells from the medium by centrifugation or filtration , precipitating the proteinaceous components of the supernatant or filtrate by means of a salt , e . g . ammonium sulfate , purification by a variety of chromatographic procedures , e . g . ion exchange chromatography or affinity chromatography , or the like . the present invention also relates to a pharmaceutical composition comprising hsp or a variant spasmolytic polypeptide of the invention together with a pharmaceutically acceptable carrier or excipient . in the composition of the invention , the variant may be formulated by any of the established methods of formulating pharmaceutical compositions , e . g . as described in remington &# 39 ; s pharmaceutical sciences , 1985 . the composition may typically be in a form suited for oral or rectal administration and may , as such , be formulated as tablets or suppositories . hsp or an sp variant of the invention is contemplated to be useful for the prophylaxis or treatment of gastrointestinal disorders . more specifically , it is contemplated for the treatment of gastric or peptic ulcers , inflammatory bowel disease , crohn &# 39 ; s disease or injury to the intestinal tract caused by radiation therapy , bacterial or other infections , etc . the invention is further illustrated in the following example with reference to the appended drawings in which fig1 shows the trefoil family of peptides . intestinal trefoil factor ( itf ) contains one trefoil domain [ 2 ], as does the breast cancer associated ps2 peptide [ 3 , 4 ]. the spasmolytic polypeptides from man , pig and mouse contain two trefoil domains [ 1 , 8 ]. spasmolysins from xenopus laevis contain one or four trefoil domains [ 10 ]. recently , a member of the frog trefoil family containing two domains has been described [ 11 ]. fig2 shows the proposed structure of human spasmolytic polypeptide , hsp . the primary amino acid sequence is taken from tomasetto et al . [ 8 ], and the disulphide bonds are placed in homology to psp [ 1 ]. fig3 shows the nucleotide sequence ( seq id no : 2 ) and corresponding amino acid sequence ( seq id no : 3 ) of the 563 bp ecori - xbai fragment encoding the leader - hsp fusion protein . the kex 2 processing site is indicated by a vertical arrow . the leader and the pcr cloned parts of the hsp gene are shown in capital letters , while the synthetic parts are shown in small letters . the underlined sequences correspond to the pcr primers with horizontal arrows indicating the direction . restriction sites relevant for the construction are shown . fig4 shows the s . cerevisiae plasmid for the expression and secretion of hsp . tpi - prom . and tpi - term . are s . cerevisiae triosephosphate isomerase transcription promoter and terminator sequences , respectively . pot is a selective marker , the schizosaccharomyces pombe triosephosphate isomerase gene . only restriction sites relevant for the construction of the plasmid have been indicated . fig5 shows reversed - phase hplc on a vydac 214tp54 column of yeast fermentation broth . the two peaks corresponding to r - hsp and glycosylated r - hsp are indicated . the dashed line shows the concentration of acetonitrile in the eluting solvent . fig6 shows ion exchance chromatography on a fast flow s column of concentrated yeast supernatant . the amount of r - hsp and glycosylated r - hsp were determined by the use of the hplc system shown in fig5 . the bars indicate the fractions pooled for further purification of r - hsp and glycosylated r - hsp . the dashed line shows the concentration of nacl in the eluting solvent . for details , see material and methods . fig7 shows the final purification of r - hsp ( a ) and glycosylated r - hsp ( b ) on a preparative reversed - phase hplc vydac 214tp1022 column . the bars indicate the fractions pooled for lyophilization . the dashed lines show the concentration of acetonitrile in the eluting solvent . for details , see material and methods . fig8 shows reversed - phase hplc on a vydac 214tp54 column of purified , glycosylated r - hsp ( a ) and r - hsp ( b ). the dashed lines show the concentration of acetonitrile in the eluting solvent . fig9 shows mass spectra of purified r - hsp ( a and b ) and glycosylated r - hsp ( c and d ). fig . a and fig . c show the original mass spectrum of r - hsp and glycosylated r - hsp , respectively . fig . b and fig . d show the reconstructed mass spectrum for r - hsp and glycosylated r - hsp on the basis of fig . a and fig . c . standard dna techniques were used as previously described [ 29 ]. synthetic oligonucleotides were prepared on an automatic dna synthesizer ( 380b , applied biosystems ) using commercially available reagents . dna sequence determinations were performed by the dideoxy chain - termination technique [ 30 ]. polymerase chain reactions ( pcr ) were performed on a dna thermal cycler ( perkin elmer cetus ) using a commercial kit ( geneamp , perkin elmer cetus ). the first trefoil domain of hsp was isolated by a pcr reaction in which 1 μg human genomic dna ( clontech , palo alto , calif ., usa ) was used as a template . the reaction mixture contained 100 pmole each of the forward primer 1 ( ggctgagcccccataacag ) ( seq id no : 4 ) and reverse primer 2 ( tggaaacaccaggggac ) ( seq id no : 5 ) ( fig3 ) and was carried out in a 100 μl volume . the cycle was : 94 ° c . for 1 min , 50 ° c . for 1 min , and 72 ° c . for 1 min . after 30 cycles a final cycle was performed in which the 72 ° c . step was maintained for 10 min . the pcr product , a 115 bp fragment , was isolated by electrophoresis on a 2 % agarose gel . the 115 bp pcr fragment was digested with ddei and then ligated to a 31 bp duplex formed from the oligonucleotides ( gagaaaccctccccctgccagtgctccaggc ) ( seq id no : 6 ) and ( tcagcctggagcactggcagggggagggtttctc ). the ligation product was amplified by pcr using forward primer 3 ( gctgagagattggagaagagagagaaaccctccccct ) ( seq id no : 7 ) and reverse primer 2 . the 3 ′ part of primer 3 is identical to the n - terminal encoding part of the hsp gene and the 5 ′ part of primer 3 is identical to the c - terminal encoding part of the hybrid leader gene ( fig3 ). in - frame fusion of the hybrid leader gene and the first trefoil domain from hsp was obtained by overlay extension pcr [ 31 ]. the product was digested with ecori and avaii and isolated as a 360 bp dna fragment . the second trefoil domain of hsp was pcr - cloned from human genomic dna as described for the first domain by replacing primers 1 and 2 with forward primer 4 ( tgcgtcatggaggtctc ) ( seq id no : 8 ) and reverse primer 5 ( agcaccatggcacttcaaag ) ( seq id no : 9 ) ( fig3 ). reverse primer 5 introduces a ncoi site as a silent mutation . the pcr product , a 115 bp fragment , was isolated and digested with ddei and ncoi resulting in a 91 bp fragment . to this fragment were ligated two synthetic duplexes . the first , encoding the amino acid sequence between the two trefoil domains , consisted of the oligonucleotides ( gtcccctggtgtttccaccccctcccaaagcaagagtcggatcagtgcgtcatggaggtc ) ( seq id no : 10 ) and ( tgagacctccatgacgcactgatccgactcttgctttgggagggggtggaaacaccaggg ) ( seq id no : 11 ). the second , a 46 bp ncoi - xbai fragment encoding the c - terminal part of hsp , consisted of the oligonucleotides ( catggtgcttcttcccgaactctgtggaagactgccattactaagt ) ( seq id no : 12 ) and ( ctagacttagtaatggcagtcttccacagagttcgggaagaagcac ) ( seq id no : 13 ). after avaii digestion a 195 bp avaii - xbai fragment was isolated . a dna construct encoding the hybrid leader fused in - frame to the entire hsp gene was obtained by ligation of the 360 bp ecori - avaii fragment and the 195 bp avaii - xbai fragment described above to the 2 . 7 kb ecori - xbai fragment from vector ptz19r [ 32 ]. this construct was then transformed into e . coli strain mt - 172 ( r − , m + ) by selection for resistance to ampicillin . dna sequencing of the resulting plasmid , kfn - 1843 , showed that the correct construction had been obtained . plasmid kfn - 1843 described above was digested with ecori and xbai . the resulting 558 bp fragment was isolated and ligated to the 9 . 3 kb ncoi - xbai fragment and the 1 . 6 kb ncoi - ecori fragment both from the yeast expression vector pmt - 636 . plasmid pmt - 636 is derived from the s . cerevisiae - e . coli shuttle vector cpot [ 25 , 33 ] by deletion of the 0 . 4 kb hpai - nrui fragment from the leu - 2 gene . the ligation mixture was trans - formed into e . coli strain mt - 172 , and the hsp expression plasmid , kfn - 1847 , was isolated ( fig4 ). plasmid pkfn - 1847 was transformed into s . cerevisiae strain mt - 663 by selection for growth on glucose as the sole carbon source . one transformant , kfn - 1852 , was selected for fermentation . the transformant described above was cultivated at 30 ° c . for 3 days in yeast peptone dextrose ( ypd ) medium [ 40 ] supplied with additional yeast extract ( 60 g / l ). an od 650 nm value of 52 was reached at the end of the fermentation . the concentration of r - hsp in the yeast fermentation broth and fractions obtained during the purification was measured by analytical hplc . aliquots ( usually 50 - 200 μl ) were injected onto a vydac 214tp54 reverse - phase c4 hplc column ( 0 . 46 × 25 cm ) equilibrated at 30 ° c . at a flow rate of 1 . 5 ml / min with 0 . 1 % ( v / v ) tfa in 5 % ( v / v ) acetonitrile . the concentration of acetonitrile in the eluting solvent was raised to 65 % ( v / v ) over 30 min . absorbance was measured at 280 nm . the peaks eluting at 15 . 6 min . and 16 . 1 min . ( fig5 ) was found by mass spectrometry analysis to represent glycosylated r - hsp and unglycosylated r - hsp , respectively . the peptides were quantified using a calibrated psp sample as standard as both peptides contain two trp and two tyr out of 106 amino acid residues . from a 10 litre fermentor , 8 litres of fermentation broth was isolated by centrifugation at 3 , 000 rpm for 10 min . the supernatant was concentrated to 0 . 9 litre using an amicon ultrafiltration unit ( ra 2000 ) equipped with an amicon spiral ultrafiltration cartridge type s1y3 , mw cutoff 3 , 000 ( product no . 540620 ). the ph was adjusted to 1 . 7 and the conductivity in the resulting concentrated sample was measured to 4 . 7 ms . the sample was pumped onto a fast flow s - sepharose ( pharmacia ) column ( 5 × 11 cm ) with a flow rate of 40 ml / h . previous to the application , the column was equilibrated in 50 mm formic acid buffer , ph = 3 . 7 . after application of the sample , the column was washed with 500 ml of 50 mm formic acid buffer , ph = 3 . 7 . the peptides were eluted from the column by a linear gradient between 1 . 5 litres of 50 mm formic acid buffer , ph = 3 . 7 and 1 . 5 litres of 50 mm formic acid buffer , ph = 3 . 7 containing 0 . 6 m nacl . fractions of 10 ml was collected at a flow rate of 40 ml / h and the absorbance was measured at 280 nm . fractions were assayed for the content of r - hsp and glycosylated r - hsp in the hplc - system previously described . the elution profile is shown in fig6 . fractions corresponding to r - hsp ( fract . nos . 107 - 128 ) and glycosylated r - hsp ( fract . nos . 78 - 95 ), respectively , were pooled . glycosylated r - hsp and r - hsp were further purified by preparative hplc chromatography . pooled fractions ( approx . 200 ml ) were pumped onto a vydac 214tp1022 c4 column ( 2 . 2 × 25 cm ) equilibrated in 0 . 1 % ( v / v ) tfa . the column was washed with 100 ml of 0 . 1 % ( v / v ) tfa in 10 % ( v / v ) mecn . the peptides were eluted at 25 ° c . and at a flow rate of 5 ml / min with a linear gradient ( 650 ml ) formed from mecn / h 2 o / tfa ( 10 . 0 : 89 . 9 : 0 . 1 v / v / v ) and mecn / h 2 o / tfa ( 60 . 0 : 39 . 9 : 0 . 1 v / v / v ). uv - absorption was monitored at 280 nm , and fractions corresponding to 10 ml were collected and analysed for the content of r - hsp or glycosylated r - hsp . fig7 shows the preparative hplc purification of r - hsp ( fig7 a ) and glycosylated r - hsp ( fig7 b ). fractions corresponding to the bars were pooled , and the volume reduced to 30 % by vacuum centrifugation . from the two resulting pools , r - hsp and glycosylated r - hsp were isolated by lyophilization . amino acid composition analysis were carried out by hydrolysis of 50 μg peptide with 6m hcl for 24 h at 110 ° c . as previously described [ 6 ]; no correction for loss during hydrolysis was carried out . amino acid sequence analysis was determined by automated edman degradation using an applied biosystems model 470a gas - phase sequencer [ 22 ]. carbohydrate composition analysis was carried out by hydrolysis of 50 μg peptide with 2m hcl for 1 h , 2 h and 4 h at 100 ° c . and monosaccharides were separated on a carbopac pai ( dionex , sunnyvale , calif .) column ( 4 × 250 mm ) eluted with 14 mm naoh . the monosaccharides were detected by pulsed amperometric detection ( dionex pad - detector ). the amount of monosaccharides was corrected to zero time of hydrolysis and calculated as nmol of monosaccharide per nmol of peptide . mass spectrometry analysis was performed using an api iii lc / ms / ms system ( sciex , thornhill , ontario , canada ). the triple quadrupole instrument has a mass - to - charge ( m / z ) range of 2400 and is fitted with a pneumatically assisted electrospray ( also referred to as ion - spray ) interface [ 23 , 24 ]. sample introduction was done by a syringe infusion pump ( sage instruments , cambridge , mass .) through a fused capillary ( 75 μm i . d .) with a liquid flow - rate set at 0 . 5 - 1 μl / min . the instrument m / z scale was calibrated with the singly - charged ammonium adduct ions of poly ( propylene glycols ) ( ppg &# 39 ; s ) under unit resolution . dna fragments encoding the two trefoil domains of hsp were isolated by pcr from human genomic dna using primers based on the published cdna sequence [ 8 ]. the full length hsp gene was obtained from the pcr cloned fragments by addition of synthetic dna fragments . the hsp gene was fused in - frame to a hybrid yeast leader sequence by overlay extension pcr [ 31 ] ( fig3 ). the hybrid leader is based on the mouse salivary amylase signal peptide [ 34 ] and the s . kluvveri α mating factor leader sequence [ 35 ] and is further modified near the kex 2 cleavage site for efficient processing [ 36 , 41 ]. the yeast expression plasmid pkfn - 1847 contains the leader - hsp gene inserted between the s . cerevisiae triose phosphate isomerase promoter and terminator [ 37 ]. the expression vector ( fig4 ) also contains the schizosaccharomyces pombe tpi gene ( pot ) [ 38 ]. the plasmid was transformed into the yeast strain mt - 663 , carrying a deletion in the tpi gene , by selecting for growth on glucose . the expression level of r - hsp in the present yeast system is approx . 120 mg / l . as can be seen from fig5 , the yeast supernatant contains two forms of r - hsp ; one eluting at r t = 15 . 6 min . and one eluting at r t = 16 . 1 min . these two forms were purified separately , and by using the analytical hplc - system ( fig5 ), these two forms can be quantified individually during the different steps of the purification . after the initial concentration of the yeast supernatant by ultrafiltration , the first purification step was cationic exchange chromatography on a fast flow s column . fig6 shows the elution profile from the column including the amount of r - hsp and glycosylated r - hsp determined in the fractions . a complete separation of the two forms of r - hsp was obtained in this step . the fractions from the fast flows s column were pooled as indicated in fig6 , and the two peptides were further purified by preparative hplc ( fig7 ). the r - hsp and glycosylated r - hsp were recovered from the fractions indicated in fig7 a and fig7 b by vacuum centrifugation and lyophilization . the purification is summarized in table 1 . the overall yield of r - hsp and glycosylated r - hsp from 8 litres of fermentation broth was 160 mg and 219 mg corresponding to 50 % and 34 %, respectively . fig8 shows the purity of r - hsp and glycosylated r - hsp as analysed by analytical hplc . from these results none of the peptides looks completely pure . however , upon rechromatography of material eluting in the minor as well as the major peak , similar chromatograms were obtained for both peptides ( results not shown ). this seems to indicate that the double peak observed for both r - hsp and glycosylated r - hsp reflects an atypical behaviour of these peptides on reverse phase columns rather than impurities in the preparations . table 2 shows the amino acid sequencing results obtained on r - hsp and glycosylated r - hsp . the average repetitive yield was 94 . 4 % ( r - hsp ) and 94 . 6 % ( glycosylated r - hsp ), respectively . in both cases the first 40 residues of the two peptides were confirmed by the sequence analysis . in the glycosylated hsp , no pth - a . a . was found in edman degradation cycle no . 15 . the hsp sequence from residue 15 - 17 ( asn - arg - thr ) corresponds to a consensus sequence for n - glycosylation of asn - 15 . the carbohydrate composition analysis of glysocylated r - hsp showed the presence of 12 . 8 nmol mannose ( man ) and 1 . 6 nmol of n - acetyl glucoseamine ( glcnac ) per nmol of r - hsp . by peptide mapping of r - hsp and glycosylated r - hsp in combination with mass spectrometry and sequencing analysis ( results not shown ), no other residue besides asn - 15 of the glycosylated r - hsp was found to be modified , i . e . no o - glycosylation was found . in fig9 , the electro - spray mass spectrometry ( esms ) analysis is shown for r - hsp and glycosylated r - hsp . fig9 a and 9c are original mass spectra displaying characteristics series of multiply charged protonated ions always observed in esms spectra of proteins . fig9 b and 9d are the corresponding computer reconstructed mass spectra from which the molecular weight of individual components may be read directly . as can be seen from fig9 b , the mw found for r - hsp is 11961 . 5 ± 2 which is in very good agreement with a calculated mass of 11961 . 3 . fig9 d shows the reconstructed ion spray mass spectrum of the glycosylated r - hsp . from the sequence analysis and the carbohydrate composition analysis , it is known that only asn - 15 is glycosylated and that only two monosaccharide residues , mannose and n - acetyl glucoseamine , occur in the glycosylated form of r - hsp . from these results in combination with the mass spectrometry data , it is possible to deduce the different glycosylated forms of r - hsp ( table 3 ). molecular weights corresponding to two series of carbohydrate side chains can be deduced from the combination of carbohydrate composition data and isms - data , namely ( glcnac ) 2 ( hex ) 10 - 15 and ( hex ) 13 - 17 ( table 3 ). as mannose is the only hexose in the glycosylated r - hsp , and as asn - 15 is the only glycosylated residue , it seems reasonable to conclude that the structure of the glycosylation site is asn -( glcnac ) 2 -( man ) 10 - 15 . the observed asn -( hex ) 13 - 17 forms are thus most likely to arise from fragmentation in the mass spectrometer , by which the two glcnac residues lose an acetyl group and are converted into two hexoses . the structure of asn -( glcnac ) 2 -( man ) 10 - 15 has previously been reported as high mannose type of n - glycosylation for other peptides and proteins expressed in yeast [ 26 ]. rio , m .- c ., chenard , m .- p ., wolf , c ., marcellin , l ., tomasetto , c ., lathe , r ., bellocq j . p . and chambon , p . 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