Abstract
Amylolytic enzymes represent a group of starch hydrolases and related enzymes that are active towards the α-glycosidic bonds in starch and related poly- and oligosaccharides. The three best known amylolytic enzymes are α-amylase, β-amylase and glucoamylase that, however, differ from each other by their amino acid sequences, three-dimensional structures, reaction mechanisms and catalytic machineries. In the sequence-based classification of all glycoside hydrolases (GHs) they have therefore been classified into the three independent families: GH13 (α-amylases), GH14 (β-amylases) and GH15 (glucoamylases). Some amylolytic enzymes have been placed to the families GH31 and GH57. The family GH13 together with the families GH70 and GH77 constitutes the clan GH-H, well-known as the α-amylase family. It contains more than 6,000 sequences and covers 30 various enzyme specificities sharing the conserved sequence regions, catalytic TIM-barrel fold, retaining reaction mechanism and catalytic triad. Among the GH13 α-amylases, those produced by plants and archaebacteria exhibit common sequence similarities that distinguish them from the α-amylases of the remaining taxonomic sources. Despite the close evolutionary relatedness between the plant and archaeal α-amylases, there are also specific differences that discriminate them from each other. These specific differences could be used in an effort to reveal the sequence-structural features responsible for the high thermostability of the α-amylases from Archaea.
Highlights
Starch is an important source of energy for a wide spectrum of animals, plants and microorganisms
The family GH77 contains only one enzyme specificity, the amylomaltase (Table 1), known as 4-α-glucanotransferase in bacteria (TERADA et al, 1999) and archaeons (KAPER et al, 2005) or disproportionating enzyme (D-enzyme) in plants (TAKAHA et al, 1993). They exhibit a lower degree of sequence similarity to the family GH13 (Fig. 4) and the main feature characteristic for the GH77 members is the lack of domain C (PRZYLAS et al, 2000) succeeding typically the catalytic TIMbarrel in GH13 (Fig. 3)
The interest in the family GH77 was recently increased by revealing the putative amylomaltases from a few borreliae that exhibited in their amino acid sequences the non-GH77 features (GODANY et al, 2008)
Summary
Starch is an important source of energy for a wide spectrum of animals (including humans), plants and microorganisms. It consists exclusively from glucose monomers that are linked by α-1,4- and α-1,6-glycosidic linkages. Amylose (15-25% of starch) is formed by α-1,4-linearly bound glucoses, whereas amylopectin (75-85% of starch) contains the branching points with the α-1,6-linked glucoses (LEVEQUE et al, 2000b; BERTOLDO and ANTRANIKIAN, 2002). Starch industry covers many well-developed and recently established sophisticated technologies that utilize amylolytic enzymes. These amylases represent approximately 30% of the worldwide industrial enzyme production, the starch hydrolysis being considered to be the main way of their use (VAN DER MAAREL et al, 2002)
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