Premium
Glycoside hydrolase family 5: structural snapshots highlighting the involvement of two conserved residues in catalysis
Author(s) -
Collet Laetitia,
Vander Wauven Corinne,
Oudjama Yamina,
Galleni Moreno,
Dutoit Raphael
Publication year - 2021
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.374
H-Index - 138
ISSN - 2059-7983
DOI - 10.1107/s2059798320015557
Subject(s) - residue (chemistry) , chemistry , glycoside hydrolase , stereochemistry , glycosylation , hydrolase , active site , glycosyl , enzyme , amino acid , biochemistry
The ability of retaining glycoside hydrolases (GHs) to transglycosylate is inherent to the double‐displacement mechanism. Studying reaction intermediates, such as the glycosyl‐enzyme intermediate (GEI) and the Michaelis complex, could provide valuable information to better understand the molecular factors governing the catalytic mechanism. Here, the GEI structure of RBcel1, an endo‐1,4‐β‐glucanase of the GH5 family endowed with transglycosylase activity, is reported. It is the first structure of a GH5 enzyme covalently bound to a natural oligosaccharide with the two catalytic glutamate residues present. The structure of the variant RBcel1_E135A in complex with cellotriose is also reported, allowing a description of the entire binding cleft of RBcel1. Taken together, the structures deliver different snapshots of the double‐displacement mechanism. The structural analysis revealed a significant movement of the nucleophilic glutamate residue during the reaction. Enzymatic assays indicated that, as expected, the acid/base glutamate residue is crucial for the glycosylation step and partly contributes to deglycosylation. Moreover, a conserved tyrosine residue in the −1 subsite, Tyr201, plays a determinant role in both the glycosylation and deglycosylation steps, since the GEI was trapped in the RBcel1_Y201F variant. The approach used to obtain the GEI presented here could easily be transposed to other retaining GHs in clan GH‐A.