Crystallographic evidence for substrate ring distortion and protein conformational changes during catalysis in cellobiohydrolase Cel6A from Trichoderma reesei
1999 (English)In: STRUCTURE WITH FOLDING & DESIGN, ISSN 0969-2126, Vol. 7, no 9, 1035-1045 p.Article in journal (Refereed) Published
BACKGROUND: Cel6A is one of the two cellobiohydrolases produced by Trichoderma reesei. The catalytic core has a structure that is a variation of the classic TIM barrel. The active site is located inside a tunnel, the roof of which is formed mainly by a pair of loops. RESULTS: We describe three new ligand complexes. One is the structure of the wild-type enzyme in complex with a nonhydrolysable cello-oligosaccharide, methyl 4-S-beta-cellobiosyl-4-thio-beta-cellobioside (Glc)(2)-S-(Glc)(2), which differs from a cellotetraose in the nature of the central glycosidic linkage where a sulphur atom replaces an oxygen atom. The second structure is a mutant, Y169F, in complex with the same ligand, and the third is the wild-type enzyme in complex with m-iodobenzyl beta-D-glucopyranosyl-beta(1,4)-D-xylopyranoside (IBXG). CONCLUSIONS: The (Glc)(2)-S-(Glc)(2) ligand binds in the -2 to +2 sites in both the wild-type and mutant enzymes. The glucosyl unit in the -1 site is distorted from the usual chair conformation in both structures. The IBXG ligand binds in the -2 to +1 sites, with the xylosyl unit in the -1 site where it adopts the energetically favourable chair conformation. The -1 site glucosyl of the (Glc)(2)-S-(Glc)(2) ligand is unable to take on this conformation because of steric clashes with the protein. The crystallographic results show that one of the tunnel-forming loops in Cel6A is sensitive to modifications at the active site, and is able to take on a number of different conformations. One of the conformational changes disrupts a set of interactions at the active site that we propose is an integral part of the reaction mechanism.
Place, publisher, year, edition, pages
1999. Vol. 7, no 9, 1035-1045 p.
cellobiohydrolase; cellulase; cellulose; crystal structure; ring distortion; CRYSTALLINE CELLULOSE DEGRADATION; SEQUENCE-BASED CLASSIFICATION; 3-DIMENSIONAL STRUCTURE; GLYCOSYL HYDROLASES; ENDOGLUCANASE-I; ACTIVE-SITE; SPECIFICITY; CELLULASES; REFINEMENT;
IdentifiersURN: urn:nbn:se:uu:diva-78209OAI: oai:DiVA.org:uu-78209DiVA: diva2:106122