Structural highlights
Publication Abstract from PubMedalpha-1,4-Glucan lyase (EC 4.2.2.13) from the red seaweed Gracilariopsis lemaneiformis cleaves alpha-1,4-glucosidic linkages in glycogen, starch and malto-oligosaccharides, yielding the keto-monosaccharide 1,5-anhydro-D-fructose. The enzyme belongs to glycoside hydrolase family 31 (GH31), but degrades starch via an elimination reaction instead of hydrolysis. The crystal structure shows that the enzyme, like GH31 hydrolases, contains a (beta/alpha)8-barrel catalytic domain with B and B' subdomains, an N-terminal domain N, and the C-terminal domains C and D. The N-terminal domain N of the lyase was found to bind a trisaccharide. Complexes of the enzyme with acarbose and 1-dexoynojirimycin, and two different covalent glycosyl-enzyme intermediates obtained with fluorinated sugar analogues show that, like GH31 hydrolases, the aspartic acid residues D553 and D665 are the catalytic nucleophile and acid, respectively. However, as a unique feature, the catalytic nucleophile is in a position to act also as a base that abstracts a proton from the C2 carbon atom of the covalently bound subsite -1 glucosyl residue, thus explaining the enzyme's unique lyase activity. One Glu to Val mutation in the active site of the homologous alpha-glucosidase from Sulfolobus solfataricus resulted in a shift from hydrolytic to lyase activity, demonstrating that a subtle amino acid difference can promote lyase activity in a GH31 hydrolase. Crystal structure of alpha-1,4-glucan lyase, a unique glycoside hydrolase family member with a novel catalytic mechanism.,Rozeboom HJ, Yu S, Madrid S, Kalk KH, Zhang R, Dijkstra BW J Biol Chem. 2013 Jul 31. PMID:23902768[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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