The 1.62 Å structure of Thermoascus aurantiacus endoglucanase: completing the structural picture of subfamilies in glycoside hydrolase family 5

Abstract

The crystal structure of Thermoascus aurantiacus endoglucanase (Cel5A), a family 5 glycoside hydrolase, has been determined to 1.62 A î resolution by multiple isomorphous replacement with anomalous scattering. It is the ¢rst report of a structure in the subfamily to which Cel5A belongs. Cel5A consists solely of a catalytic module with compact eight-fold L L/K K barrel architecture. The length of the tryptophan-rich substrate binding groove suggests the presence of substrate binding subsites 3 34 to +3. Structural comparison shows that two glycines are completely conserved in the family, in addition to the two catalytic glutamates and six other conserved residues previously identi¢ed. Gly 44 in particular is part of a type IV C-terminal helix capping motif, whose disruption is likely to a¡ect the position of an essential conserved arginine. One aromatic residue (Trp 170 in Cel5A), not conserved in term of sequence, is nonetheless spatially conserved in the substrate binding groove. Its role might be to force the bend that occurs in the polysaccharide chain on binding, thus favoring substrate distortion at subsite 3 31. ß 2002 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

Genomics Review of Holocellulose Deconstruction by Aspergilli

“…The catalytic core domain of Cel5A from T. reesei determined at 2.05 Å shows a substrate-binding pocket consisting of a deep catalytic cleft within a shallow groove, consistent with other structural studies of GH5 endoglucanases (115). The Thermoascus aurantiacus GH5 endoglucanase, which consists of a catalytic module with compact 8-fold ␤/␣-barrel architecture (116), has a long, tryptophan-rich substrate-binding groove suggesting substrate-binding subsites at positions Ϫ4 to ϩ3, in addition to the two conserved catalytic glutamates (116).…”

“…The three-dimensional structures are for the Thermoascus aurantiacus GH5 endoglucanase Cel5A (PDB entry 1GZJ), the Trichoderma reesei GH7 enzyme EGI (PDB entry 1EG1), and the Trichoderma reesei GH12 enzyme EGIII (Egl3 or Cel12A; PDB entry 1H8V) (116,119,122). common to all aspergilli and have structurally similar catalytic domains (Fig.…”

Processive Endoglucanases Mediate Degradation of Cellulose by Saccharophagus degradans

“…To evaluate whether Cel5H is an endoglucanase like other GH5 enzymes (20), its effect on the viscosity of CMC solutions was monitored. S. degradans Cel5H rapidly decreased the viscosity of CMC similarly to the endoglucanase T. fusca Cel9B (a gift from D. Wilson).…”

Biochemical Characterization and Structural Analysis of a Bifunctional Cellulase/Xylanase from Clostridium thermocellum

“…hydrogen bonds to C2-OH of the bound cellulodextrins (26 -28) or can better tolerate an equatorial or axial 2-OH because of the relatively flexible structures (6,29). In contrast, the Asn-208 side chain of CtCel5E cannot form a hydrogen bond with the axial 2-OH.…”

“…Lic26A is a glycoside hydrolase (GH) 4 family 26 hydrolase that contains ␤-1,3-1,4-mixed linked endoglucanase activity (4,5). Cel5E is a bifunctional ␤-1,4-endoglucanase/xylanase that belongs to the GH5 family (6,7), and GH5 is the second largest among the 133 GH families (see the CAZy database) (8). Because Cel5E is a bifunctional cellulase/xylanase and xylan is the major component of hemicelluloses in plants, it would be beneficial to understand the structure and function of Cel5E.…”