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Abstract
Amylomaltases (4-α-glucanotransferases, E.C. 2.4.1.25) are enzymes which can perform a double-step catalytic process, resulting in a transglycosylation reaction. They hydrolyse glucosidic bonds of α-1,4′-d-glucans and transfer the glucan portion with the newly available anomeric carbon to the 4′-position of an α-1,4′-d-glucan acceptor. The intramolecular reaction produces a cyclic α-1,4′-glucan. Amylomaltases can be found only in prokaryotes, where they are involved in glycogen degradation and maltose metabolism. These enzymes are being studied for possible biotechnological applications, such as the production of (i) sugar substitutes; (ii) cycloamyloses (molecules larger than cyclodextrins), which could potentially be useful as carriers and encapsulating agents for hydrophobic molecules and also as effective protein chaperons; and (iii) thermoreversible starch gels, which could be used as non-animal gelatin substitutes. Extremophilic prokaryotes have been investigated for the identification of amylomaltases to be used in the starch modifying processes, which require high temperatures or extreme conditions. The aim of this article is to present an updated overview of studies on amylomaltases from extremophilic Bacteria and Archaea, including data about their distribution, activity, potential industrial application and structure.
Highlights
Amylomaltases are prokaryotic 4-α-glucanotransferases (4α-GTases) of the CAZy glycoside hydrolase (GH) family GH77 [1], accessed on 3 Sepetember 2021
In comparison with the mesophilic enzyme (A0A0E1EIJ0 from S. agalactiae), while the bacterial thermophilic enzymes show a higher number of hydrogen bonds (HBs), the same does not happen for the archaeal enzymes
From the analysis of amino acid composition, it appears that, at least for thermophilic amylomaltases, some specific compositions might be the basis of enzyme stability
Summary
Amylomaltases are prokaryotic 4-α-glucanotransferases (4α-GTases) of the CAZy glycoside hydrolase (GH) family GH77 [1], accessed on 3 Sepetember 2021. D-enzymes are involved in the synthesis of CDs, while amylomaltases produce the larger CAs. Amylomaltases in prokaryotes have been associated with different functions. The interest in amylomaltases is due to their ability to modify starch and the consequent wide range of applications in the food and pharmaceutical fields In this regard, several studies have been carried out on amylomaltases from extremophiles as potentially more robust enzymes, better suited for industrial processes. Structural data are compared with those of amylomaltases from mesophilic bacteria to highlight differences between the enzymes, which are possibly related to their different activity in extreme conditions This analysis may be of interest for studies aimed at understanding the structure/activity relationships for this class of enzymes and, possibly, lays the groundwork to design amino acid mutations for further enzyme optimization
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