1qjw: Difference between revisions

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.

1QJW is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Hypocrea_jecorina Hypocrea jecorina] with NAG, MAN, CD and GOL as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Cellulose_1,4-beta-cellobiosidase Cellulose 1,4-beta-cellobiosidase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.91 3.2.1.91] Structure known Active Sites: ST1 and ST2. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1QJW OCA].  

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