1qjw
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CEL6A (Y169F) WITH A NON-HYDROLYSABLE CELLOTETRAOSE
OverviewOverview
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.
About this StructureAbout this Structure
1QJW is a Single protein structure of sequence from Hypocrea jecorina with NAG, MAN, CD and GOL as ligands. Active as Cellulose 1,4-beta-cellobiosidase, with EC number 3.2.1.91 Structure known Active Sites: ST1 and ST2. Full crystallographic information is available from OCA.
ReferenceReference
Crystallographic evidence for substrate ring distortion and protein conformational changes during catalysis in cellobiohydrolase Ce16A from trichoderma reesei., Zou J, Kleywegt GJ, Stahlberg J, Driguez H, Nerinckx W, Claeyssens M, Koivula A, Teeri TT, Jones TA, Structure. 1999 Sep 15;7(9):1035-45. PMID:10508787
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