Crystal Structure of Thermobifida fusca Endoglucanase Cel6A in Complex with Substrate and Inhibitor:  The Role of Tyrosine Y73 in Substrate Ring Distortion

• Published in: Biochemistry (Easton) Vol. 44; no. 39; pp. 12915 - 12922
• Main Authors: Larsson, Anna M, Bergfors, Terese, Dultz, Elisa, Irwin, Diana C, Roos, Annette, Driguez, Hugues, Wilson, David B, Jones, T. Alwyn
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 04.10.2005
• Subjects: Bacterial Proteins - chemistry; Catalytic Domain; Cellobiose - chemistry; Cellulase - antagonists & inhibitors; Cellulase - chemistry; Cellulose - analogs & derivatives; Cellulose - chemistry; Crystallography, X-Ray; Enzyme Inhibitors - chemistry; Protein Binding; Substrate Specificity; Tetroses - chemistry; Thermobifida fusca; Tyrosine
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi0506730

Endoglucanase Cel6A from Thermobifida fusca hydrolyzes the β-1,4 linkages in cellulose at accessible points along the polymer. The structure of the catalytic domain of Cel6A from T. fusca in complex with a nonhydrolysable substrate analogue that acts as an inhibitor, methylcellobiosyl-4-thio-β-cellobioside (Glc2-S-Glc2), has been determined to 1.5 Å resolution. The glycosyl unit in subsite −1 was sterically hindered by Tyr73 and forced into a distorted 2So conformation. In the enzyme where Tyr73 was mutated to a serine residue, the hindrance was removed and the glycosyl unit in subsite −1 had a relaxed 4C1 chair conformation. The relaxed conformation was seen in two complex structures of the mutated enzyme, with cellotetrose (Glc4) at 1.64 Å and Glc2-S-Glc2 at 1.04 Å resolution.