Abstract:
The present invention relates to thermostable pullulanases useful for industrial and scientific purposes. The present invention provides methods for producing the modified pullulanase, enzymatic compositions comprising the modified pullulanase, and methods for use of the enzymatic compositions.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to enzymes, polynucleotides encoding the enzymes, the use of such polynucleotides and polypeptides, and more specifically to enzymes having pullulanase activity. 
       SEQUENCE LISTING 
       [0002]    This application is being filed electronically via the USPTO EFS-WEB server, as authorized and set forth in MPEP §502.05 and this electronic filing includes an electronically submitted sequence listing; the entire content of this sequence listing is hereby incorporated by reference into the specification of this application. The sequence listing is identified on the electronically filed ASCII (.txt) text file as follows: 
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       BACKGROUND 
       [0003]    Pullulanase is a specific kind of glucanase, an amylolytic exoenzyme, that degrades pullulan. Type I pullulanases specifically attack alpha-1,6 linkages, while type II pullulanases are also able to hydrolyse alpha-1,4 linkages. 
         [0004]    Pullulanase (EC 3.2.1.41) is also known as pullulan-6-glucanohydrolase (Debranching enzyme). Its substrate, pullulan, is regarded as a chain of maltotriose units linked by alpha-1,6-glycosidic bonds. Pullulanase will hydrolytically cleave pullulan (alpha-glucan polysaccharides). 
         [0005]    Pullulanases are used for several industrial and commercial applications, including, saccharification of starch, liquefaction of starch, production of high-maltose corn syrup, production of high-fructose corn syrup, starch processing, in detergents, production of cyclodextrins, and production of low-calorie beer, in the baking industry, as well as dental plaque control. (Siew Ling Hii, Joo Shun Tan, Tau Chuan Ling, and Arbakariya Bin Ariff, “Pullulanase: Role in Starch Hydrolysis and Potential Industrial Applications,” Enzyme Research, vol. 2012, Article ID 921362, 14 pages, 2012.) 
       SUMMARY OF THE INVENTION 
       [0006]    The invention provides an isolated nucleic acid having a sequence as set forth in SEQ ID No.: 1 and variants thereof having at least 50% sequence identity to SEQ ID No.: 1 and encoding polypeptides having pullulanase activity, or encoding polypeptides having pullulanase activity having at least 50% sequence identity to SEQ ID No.: 2. 
         [0007]    One aspect of the invention is an isolated nucleic acid having a sequence as set forth in SEQ ID No.: 1, sequences substantially identical thereto, and sequences complementary thereto. 
         [0008]    Another aspect of the invention is an isolated nucleic acid including at least 10 consecutive bases of a sequence as set forth in SEQ ID No: 1 nucleic acid sequences, sequences substantially identical thereto, and the sequences complementary thereto. 
         [0009]    In yet another aspect, the invention provides an isolated nucleic acid encoding a polypeptide having a sequence as set forth in SEQ ID No.: 2 and variants thereof encoding a polypeptide having pullulanase activity and having at least 50% sequence identity to such sequences. Another aspect of the invention is an isolated nucleic acid encoding a polypeptide or a functional fragment thereof having a sequence as set forth in SEQ ID No.: 2, and sequences substantially identical thereto. 
         [0010]    Another aspect of the invention is an isolated nucleic acid encoding a polypeptide having at least 10 consecutive amino acids of a sequence as set forth in SEQ ID No.: 2, and sequences substantially identical thereto. 
         [0011]    In yet another aspect, the invention provides a purified polypeptide having a sequence as set forth in SEQ ID No.: 2, and sequences substantially identical thereto 
         [0012]    Another aspect of the invention is a method of making a polypeptide having a sequence as set forth in SEQ ID No.: 2, and sequences substantially identical thereto. The method includes introducing a nucleic acid encoding the polypeptide into a host cell, wherein the nucleic acid is operably linked to a promoter, and culturing the host cell under conditions that allow expression of the nucleic acid. 
         [0013]    Another aspect of the invention is a method of making a polypeptide having SEQ ID No.: 2, and sequences substantially identical thereto. The method includes introducing a nucleic acid encoding the polypeptide into a host cell, wherein the nucleic acid is operably linked to a promoter, and culturing the host cell under conditions that allow expression of the nucleic acid, thereby producing the polypeptide. 
         [0014]    Another aspect of the invention is a method of generating a variant including obtaining a nucleic acid having a sequence as set forth in SEQ ID No.: 1 or sequences substantially identical thereto, sequences complementary to the sequences of SEQ ID No.: 1, fragments comprising at least 30 consecutive nucleotides of the foregoing sequences, and changing one or more nucleotides in the sequence to another nucleotide, deleting one or more nucleotides in the sequence, or adding one or more nucleotides to the sequence. 
         [0015]    Another aspect of the invention is a computer readable medium having stored thereon a sequence as set forth in SEQ ID No.: 1 sequences, and sequences substantially identical thereto, or a polypeptide sequence as set forth in SEQ ID No.: 2 amino acid sequences, and sequences substantially identical thereto. 
         [0016]    Another aspect of the invention is an assay for identifying fragments or variants of SEQ ID No.: 2 amino acid sequences, and sequences substantially identical thereto, which retain the enzymatic function of the polypeptides of SEQ ID No.: 2 amino acid sequences, and sequences substantially identical thereto. The assay includes contacting the polypeptide of SEQ ID No.: 2 amino acid sequences, sequences substantially identical thereto, or polypeptide fragment or variant with a substrate molecule under conditions which allow the polypeptide fragment or variant to function, and detecting either a decrease in the level of substrate or an increase in the level of the specific reaction product of the reaction between the polypeptide and substrate thereby identifying a fragment or variant of such sequences. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The following drawings are illustrative of embodiments of the invention and are not meant to limit the scope of the invention as encompassed by the claims. 
           [0018]      FIG. 1  is a chromatogram displaying the results of a digestion using the pullulanase of SEQ ID No.: 1 &amp; 2 with a 1% corn starch substrate at 50 degrees Celcius, and as further described in Example 1. 
           [0019]      FIG. 2  is a chromatogram displaying the results of a digestion using the pullulanase of SEQ ID No.: 1 &amp; 2 with a 1% pullulan at 50 degrees Celcius, and as further described in Example 1. 
           [0020]      FIG. 3  is a chromatogram displaying the results of a digestion using the pullulanase of SEQ ID No.: 1 &amp; 2 with a 1% corn starch substrate at 75 degrees Celcius, and as further described in Example 1. 
           [0021]      FIG. 4  is SEQ ID No.: 1, the deoxyribonucleic acid (DNA) sequence of the present invention. 
           [0022]      FIG. 5  is SEQ ID No.: 2, the amino acid sequence of the present invention. 
       
    
    
     EXAMPLES 
     Example 1 
       [0023]    The pullulanase of the present invention (as embodied by SEQ ID No.: 1 &amp; 2) was tested against 1% solids using an aliquot from a trial cell lysate. The results shown in  FIGS. 1 ,  2 , and  3 , show that the pullulanase of the present invention is able to cleave both alpha-1,6 and alpha-1,4 bonds. As displayed in  FIG. 2 , the pullulanase of the present invention (as embodied by SEQ ID No. 1 &amp; 2) was assayed with 1% pullulan at 50 degrees Celsius. As displayed in  FIG. 1 , the pullulanase of the present invention (as embodied by SEQ ID NO 1 &amp; 2) was assayed with 1% corn starch at 50 degrees Celcius. As displayed in  FIG. 3 , the pullulanase of the present invention (as embodied by SEQ ID No. 1 &amp; 2) was assayed with 1% corn starch at 75 degrees Celsius. As indicated in  FIGS. 1 ,  2 , and  3 , the enzyme is a type II pullulanase, as the reaction products (major peaks) are glucose, maltose, and maltotriose. Additionally, the peak  2  product was confirmed to be maltose and not isomaltose, while the peak  3  product was confirmed to be maltotriose and not panose. 
       Example 2 
       [0024]    The pullulanase of the present invention (as embodied by SEQ ID No. 1 &amp; 2) melting point or thermal denaturation was determined using differential scanning calorimetry. The Tm of the present invention (as embodied by SEQ ID No. 1 &amp; 2) is 84 degrees Celsius. 
       DETAILED DESCRIPTION 
       [0025]    The present invention relates to a pullulanase enzyme, polynucleotides encoding the enzymes, methods of making and using these polynucleotides and polypeptides. The invention is directed to novel polypeptides having pullulanase activity, nucleic acids encoding them. The polypeptides of the invention can be used in a variety of commercial, medical, and industrial contexts. The polypeptides of the invention can be used as, e.g., an additive for a detergent, for processing foods and for chemical synthesis utilizing a reverse reaction, saccharification of starch, liquefaction of starch, production of high-maltose corn syrup, production of high-fructose corn syrup, starch processing, ethanol production, production of cyclodextrins, and production of low-calorie beer, in the baking industry, as well as dental plaque control. 
         [0026]    In one aspect of the invention the pullulanase is a type II pullulanase or is capable of cleaving both alpha-1,6 and alpha-1,4 bonds. In another aspect of the invention the pullulanase of the present invention is capable of cleaving both alpha-1,6 and alpha-1,4 of pullulan yielding glucose, maltose, and maltotriose. In a further embodiment of the present invention the pullulanase of the present invention is thermostable and or thermotolerant. In a further embodiment of the invention the pullulanase of the present invention is active at 75 degrees Celsius. In a further embodiment of the invention, the pullulanase of the invention is capable of saccharification of starch at higher temperatures then currently employed, thereby reducing processing times, and increasing yields due to lessening the rate of retrogradation of materials resulting in drops in temperature. In a further embodiment of the present invention the pullulanase is capable of enhancing ethanol or glucose production by digesting limit dextrans that an amylase cannot digest. 
         [0027]    In a further embodiment of the present invention the pullulanase of the present invention is coupled with an amylase enzyme. 
         [0028]    In one aspect, the nucleic acid encodes at least one polypeptide having pullulanase activity. 
         [0029]    “Synthetic” nucleic acids (including oligonucleotides), polypeptides or proteins of the invention include those prepared by any chemical synthesis, e.g., as described, below. 
         [0030]    The phrases “nucleic acid” or “nucleic acid sequence” includes oligonucleotides, nucleotides, polynucleotides, or to a fragment of any of these, to DNA or RNA (e.g., mRNA, rRNA, tRNA) of genomic, recombinant or synthetic origin which may be single-stranded or double-stranded and may represent a sense or antisense strand, to peptide nucleic acid (PNA), or to any DNA-like or RNA-like material, natural or synthetic in origin, including, e.g., iRNA such as miRNA or siRNA, ribonucleoproteins (e.g., iRNPs). The term encompasses nucleic acids, i.e., oligonucleotides, containing known analogues of natural nucleotides. The term also encompasses nucleic-acid-like structures with synthetic backbones, see e.g., Mata (1997) Toxicol. Appl. Pharmacol. 144:189-197; Strauss-Soukup (1997) Biochemistry 36:8692-8698; Samstag (1996) Antisense Nucleic Acid Drug Dev 6:153-156. 
         [0031]    “Recombinant” polypeptides or proteins refer to polypeptides or proteins produced by recombinant DNA techniques; e.g., produced from cells transformed by an exogenous DNA construct encoding the desired polypeptide or protein. 
         [0032]    The term “gene” includes a nucleic acid sequence comprising a segment of DNA involved in producing a transcription product (e.g., a message), which in turn is translated to produce a polypeptide chain, or regulates gene transcription, reproduction or stability. Genes can include regions preceding and following the coding region, such as leader and trailer, promoters and enhancers, as well as, where applicable, intervening sequences (introns) between individual coding segments (exons). 
         [0033]    The invention provides isolated and recombinant nucleic acids, including expression cassettes such as expression vectors encoding the polypeptides of the invention. The invention provides probes comprising or consisting of nucleic acids of the invention. The invention also includes methods for discovering new pullulanase sequences using the nucleic acids of the invention. The invention also includes methods for inhibiting the expression of pullulanase genes, transcripts and polypeptides using the nucleic acids of the invention. 
         [0034]    The nucleic acids of the invention can be made, isolated and/or manipulated by, e.g., cloning and expression of cDNA libraries, amplification of message or genomic DNA by PCR, and the like. In practicing the methods of the invention, homologous genes can be modified by manipulating a template nucleic acid, as described herein. The invention can be practiced in conjunction with any method or protocol or device known in the art, which are well described in the scientific and patent literature.