Structural highlights
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[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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