Amylomaltases in Extremophilic Microorganisms

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.

Identification of an Amylomaltase from the Halophilic Archaeon Haloquadratum walsbyi by Functional Metagenomics: Structural and Functional Insights

“…BLASTP analysis of the 48-amino-acid insert did not provide significant results. The H. walsbyi enzyme was also characterized by a high percentage of acidic amino acids (16.7%), the highest value detected so far among extreme amylomaltases [25]. This reflects the origin of the enzyme from a halophilic archaeal microorganism.…”

“…Amylomaltases are gaining interest in the food and pharmaceutical industries for their ability to modify starch, and several enzymes from thermophilic and hyper-thermophilic prokaryotes have already been produced as recombinant molecules and characterized [25]. Since amylomaltases from halophilic microorganisms have never been isolated, we considered it interesting to characterize the putative H. walsbyi enzyme.…”

“…For plants, structures have been determined for Arabidopsis thaliana [19] and potato [20]. For bacteria, structures have been obtained for amylomaltases from Aquifex aeolicus (Protein Data Bank, PDB, accession number 1TZ7), Corynebacterium glutamicum [21], E. coli [22], Streptococcus agalactiae [23], Thermus brockianus [24], T. thermophilus AT-62 (formerly indicated as T. aquaticus [25]) [26]. No structural studies are available for amylomaltases from Archaea.…”

“…Amylomaltases have aroused interest for biotechnological applications, as they have been found useful for the production of (i) slow digestible starch, a modified starch with a reduced susceptibility to enzymatic hydrolyses, useful for the production of foods with a low glycemic index; (ii) cycloamyloses, circular α-1,4-glucans containing up to a few hundred glucose units, with possible applications as carrier in the food, pharmaceutical and chemical industries; (iii) thermoreversible starch gels, as substitute for animal gelatin in the food industry (see [25] and references therein). Even if several studies on amylomaltases from thermophilic and hyper-thermophilic bacteria and Archaea have been carried out, amylomaltases from halophiles have never been studied.…”

Production of Large-Ring Cyclodextrins by Amylomaltases

“…Nakapong et al, 2022 focused on heterologous expression of 4αGTases including CGTase and amylomaltase for overproduction and beneficial properties for industrial applications [10]. Leoni and co-workers emphasized thermostability of amylomaltases from the extremophiles [11]. Ahmad et al, 2015 provided a review of structural similarities and mechanism of thermostable 4αGTases in comparison with other starch processing enzymes from other glycoside hydrolase (GH) families [12].…”