4b9z
Crystal Structure of Agd31B, alpha-transglucosylase, complexed with Acarbose
Structural highlights
FunctionOL4AG_CELJU Alpha-transglucosylase that specifically transfers single glucosyl units from alpha(1->4)-glucans to the non-reducing terminal 4-OH of glucose and alpha(1->4)- and alpha(1->6)-linked glucosyl residues. Acts on amylose, amylopectin, glycogen and maltooligosaccharides, with the highest activity with maltotriose as a donor, and also accepts maltose. Does not act as a hydrolase: weak hydrolysis activity is only observed on the disaccharide maltose.[1] Publication Abstract from PubMedThe metabolism of the storage polysaccharides glycogen and starch are of vital importance to organisms from all domains of life. In bacteria, utilization of these alpha-glucans requires the concerted action of a variety of enzymes, including glycoside hydrolases, glycoside phosphorylases, and transglycosylases. In particular, transglycosylases from glycoside hydrolase families GH13 and GH77 play well-established roles in alpha-glucan sidechain (de)branching, regulation of oligo- and polysaccharide chain length, and formation of cyclic dextrans. Here, we present the biochemical and tertiary structural characterization of a new type of bacterial 1,4-alpha-glucan 4-alpha-glucosyltransferase from glycoside hydrolase family 31 (GH31). Distinct from 1,4-alpha-glucan 6-alpha-glucosyltransferases (EC 2.4.1.24) and 4-alpha-glucanotransferases (EC 2.4.1.25), this enzyme strictly transferred one glucosyl residue from alpha(1 -->4) glucans in disproportionation reactions. Substrate hydrolysis was undetectable for a series of malto-oligosaccharides, except maltose, for which transglycosylation nonetheless dominated across a range of substrate concentrations. Crystallographic analysis of the enzyme in apo, acarbose-complexed, and trapped 5-beta-fluoroglucosyl-enzyme intermediate forms revealed extended substrate interactions across one negative and up to three positive subsites, thus providing structural rationalization for the unique, single-monosaccharide transferase activity of the enzyme. Structural enzymology of Cellvibrio japonicus Agd31B reveals alpha-transglucosylase activity in glycoside hydrolase family 31.,Larsbrink J, Izumi A, Hemsworth GR, Davies GJ, Brumer H J Biol Chem. 2012 Nov 6. PMID:23132856[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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