title: Crystal structure of Cel44A, a glycoside hydrolase family 44 endoglucanase from Clostridium thermocellum.
abstract: The crystal structure of Cel44A, which is one of the enzymatic components of the cellulosome of Clostridium thermocellum, was solved at a resolution of 0.96 A. This enzyme belongs to glycoside hydrolase family (GH family) 44. The structure reveals that Cel44A consists of a TIM-like barrel domain and a beta-sandwich domain. The wild-type and the E186Q mutant structures complexed with substrates suggest that two glutamic acid residues, Glu(186) and Glu(359), are the active residues of the enzyme. Biochemical experiments were performed to confirm this idea. The structural features indicate that GH family 44 belongs to clan GH-A and that the reaction catalyzed by Cel44A is retaining type hydrolysis. The stereochemical course of hydrolysis was confirmed by a (1)H NMR experiment using the reduced cellooligosaccharide as a substrate.
authors: Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 0600810, Japan.
authors: Yu
authors: Y
authors: Kitago
authors: Shuichi
authors: S
authors: Karita
authors: Nobuhisa
authors: N
authors: Watanabe
authors: Masakatsu
authors: M
authors: Kamiya
authors: Tomoyasu
authors: T
authors: Aizawa
authors: Kazuo
authors: K
authors: Sakka
authors: Isao
authors: I
authors: Tanaka
mesh_terms: D019943:Amino Acid Substitution; D002480:Cellulase / Q000737:chemistry* / Q000235:genetics; D048013:Acetivibrio thermocellus / Q000201:enzymology* / Q000235:genetics; D018360:Crystallography, X-Ray; D006868:Hydrolysis; D020125:Mutation, Missense; D009844:Oligosaccharides / Q000737:chemistry; D017433:Protein Structure, Secondary / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D013379:Substrate Specificity / Q000235:genetics
chemical_list: D009844:Oligosaccharides; D002480:Cellulase