REFERENCE TO SEQUENCE LISTING
This application contains a Sequence Listing in computer readable form, which is incorporated herein by reference.
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OF THE INVENTION
1. Field of the Invention
The present invention relates to alpha-amylase variants, polynucleotides encoding the variants, methods of producing the variants, and methods of using the variants.
2. Description of Related Art
Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 184.108.40.206) constitute a group of enzymes, which catalyze the hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
Alpha-amylases are used commercially for a variety of purposes such as in the initial stages of starch processing (e.g., liquefaction); in wet milling processes; and in alcohol production from carbohydrate sources. They are also used as cleaning agents or adjuncts in detergent matrices; in the textile industry for starch desizing; in baking applications; in the beverage industry; in oil fields in drilling processes; in recycling processes, e.g., for de-inking paper; and in animal feed.
One of the first bacterial alpha-amylases to be used was an alpha-amylase from B. licheniformis, also known as Termamyl™, which has been extensively characterized and the crystal structure has been determined for this enzyme. Alkaline amylases, such as the alpha-amylase derived from Bacillus sp. strains NCIB 12289, NCIB 12512, NCIB 12513, and DSM 9375 (disclosed in WO 95/26397), form a particular group of alpha-amylases that are useful in detergents. Many of these known bacterial amylases have been modified in order to improve their functionality in a particular application.
Termamyl™ and many highly efficient alpha-amylases require calcium for activity. The crystal structure of Termamyl™ shows that three calcium atoms are bound to the alpha-amylase structure coordinated by negatively charged amino acid residues. This requirement for calcium is a disadvantage in applications where strong chelating compounds are present, such as in detergents or during ethanol production from whole grains, where the plant material comprises a large amount of natural chelators such as phytate.
Calcium-insensitive amylases are known, e.g., the alpha-amylases disclosed in EP 1022334 and WO 03/083054, and a Bacillus circulans alpha-amylase having the sequence disclosed in UNIPROT:Q03657.
It would therefore be beneficial to provide alpha-amylases with reduced calcium sensitivity.
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OF THE INVENTION
The present invention provides alpha-amylase variants comprising an A-domain of a calcium-sensitive alpha-amylase, a B-domain which has at least 55% and less than 100% sequence identity with the B-domain of SEQ ID NO: 13, and a C-domain of a calcium-sensitive alpha-amylase.
The present invention also relates to isolated polynucleotides encoding an alpha-amylase variant, nucleic acid constructs, vectors, and host cells comprising the polynucleotides, and methods of producing a variant of a parent alpha-amylase.
The present invention also relates to the use of the variants in starch processing (e.g., liquefaction); wet milling processes; alcohol production from carbohydrate sources; detergents; dishwashing compositions; starch desizing in the textile industry; baking applications; the beverage industry; oil fields in drilling processes; recycling processes, e.g., for de-inking paper, and animal feed.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 shows an alignment of SEQ ID NOS: 1-16, 29 and 30.
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OF THE INVENTION
The present invention provides alpha-amylase variants comprising an A-domain of a calcium-sensitive alpha-amylase, a B-domain which has at least 50% and less than 100% sequence identity with the B-domain of SEQ ID NO: 13, and a C-domain of a calcium-sensitive alpha-amylase.
A, B and C-Domains: The structure of alpha-amylases comprises three distinct domains A, B and C, see, e.g., Machius et al., 1995, J. Mol. Biol. 246: 545-559. The term “domain” means a region of a polypeptide that in itself forms a distinct and independent substructure of the whole molecule. Alpha-amylases consist of a beta/alpha-8 barrel harboring the active site, which is denoted the A-domain, a rather long loop between the beta-sheet 3 and alpha-helix 3, which is denoted the B-domain, and a C-domain and in some cases also a carbohydrate binding domain (e.g., WO 2005/001064; Machius et al., supra).
The domains of an alpha-amylase can be determined by structure analysis such as by using crystallographically techniques. An alternative method for determining the domains of an alpha-amylase is by sequence alignment of the amino acid sequence of the alpha-amylase with another alpha-amylase for which the domains have been determined. The sequence that aligns with, e.g., the B-domain sequence in the alpha-amylase for which the B-domain has been determined can be considered the B-domain for the given alpha-amylase.
Allelic variant: The term “allelic variant” means any of two or more alternative forms of a gene occupying the same chromosomal locus. Allelic variation arises naturally through mutation, and may result in polymorphism within populations. Gene mutations can be silent (no change in the encoded polypeptide) or may encode polypeptides having altered amino acid sequences. An allelic variant of a polypeptide is a polypeptide encoded by an allelic variant of a gene.
Alpha-amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 220.127.116.11) are a group of enzymes, which catalyze the hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
Calcium-insensitive amylase means an alpha-amylase that does not require the presence of calcium for optimal activity and/or for maintaining the active conformation/structure.
Calcium-sensitive amylase means an alpha-amylase that requires the presence of calcium to retain its structure and/or to have full enzymatic activity. For some calcium-sensitive amylases it has been shown that they contains a calcium atom coordinated to acidic amino acid residues in the active conformation. A large number of calcium-sensitive alpha-amylases are known and have been used industrially because of their beneficial properties. Calcium-sensitive alpha-amylases are generally sensitive towards conditions that leads to loss of the calcium atom coordinated in their structure such as detergent compositions and fuel mass.
Calcium sensitivity is determined by incubating an alpha-amylase in the presence of a strong chelator and analyzing the impact of this incubation on the activity or stability of the alpha-amylase. A calcium-sensitive alpha-amylase will be less stable in the presence of a chelator or lose a major part or all of its activity during incubation whereas a calcium-insensitive alpha-amylase will not lose all of its activity or will lose only a minor part of the activity during incubation. Chelator strength may be evaluated using methods known in the art such as the methods disclosed in Nielsen et al., 2003, Anal. Biochem. 314: 227-234; and Nagarajan and Paine, 1984, J. Am. Oil Chem. Soc. 61(9): 1475-1478. Examples of strong chelators that may be used for such an assay are EGTA (ethylene glycol tetraacetic acid), EDTA (ethylene diamine tetraacetic acid), DTPA (diethylene triamine pentaacetic acid), DTMPA (diethylene triamine-penta-methylene phosphonic acid) and HEDP (1-hydroxyethan-1,1-diylbis(phosphonic acid)). Other strong chelators may be used to determine the calcium sensitivity of an alpha-amylase.
Coding sequence: The term “coding sequence” means a polynucleotide, which directly specifies the amino acid sequence of its polypeptide product. The boundaries of the coding sequence are generally determined by an open reading frame, which usually begins with the ATG start codon or alternative start codons such as GTG and TTG and ends with a stop codon such as TAA, TAG, and TGA. The coding sequence may be a DNA, cDNA, synthetic, or recombinant polynucleotide.
Control sequence: The term “control sequence” means all components necessary for the expression of a polynucleotide encoding a variant of the present invention. Each control sequence may be native or foreign to the polynucleotide encoding the variant or native or foreign to each other. Such control sequences include, but are not limited to, a leader, polyadenylation sequence, propeptide sequence, promoter, signal peptide sequence, and transcription terminator. At a minimum, the control sequences include a promoter, and transcriptional and translational stop signals. The control sequences may be provided with linkers for the purpose of introducing specific restriction sites facilitating ligation of the control sequences with the coding region of the polynucleotide encoding a variant.
Expression: The term “expression” includes any step involved in the production of the polypeptide including, but not limited to, transcription, post-transcriptional modification, translation, post-translational modification, and secretion.
Expression vector: The term “expression vector” means a linear or circular DNA molecule that comprises a polynucleotide encoding a polypeptide of the present invention and is operably linked to additional nucleotides that provide for its expression.