1gmm: Difference between revisions

Polysaccharide-degrading enzymes are generally modular proteins that, contain non-catalytic carbohydrate-binding modules (CBMs), which, potentiate the activity of the catalytic module. CBMs have been grouped, into sequence-based families, and three-dimensional structural data are, available for half of these families. Clostridium thermocellum xylanase, 11A is a modular enzyme that contains a CBM from family 6 (CBM6), for, which no structural data are available. We have determined the crystal, structure of this module to a resolution of 2.1 A. The protein is a, beta-sandwich that contains two potential ligand-binding clefts designated, cleft A and B. The CBM interacts primarily with xylan, and NMR, spectroscopy coupled with site-directed mutagenesis identified cleft A, containing Trp-92, Tyr-34, and Asn-120, as the ligand-binding site. The, overall fold of CBM6 is similar to proteins in CBM families 4 and 22, although surprisingly the ligand-binding site in CBM4 and CBM22 is, equivalent to cleft B in CBM6. These structural data define a superfamily, of CBMs, comprising CBM4, CBM6, and CBM22, and demonstrate that, although, CBMs have evolved from a relatively small number of ancestors, the, structural elements involved in ligand recognition have been assembled at, different locations on the ancestral scaffold.

1GMM is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Clostridium_thermocellum Clostridium thermocellum] with SO4, NA and CA as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Endo-1,4-beta-xylanase Endo-1,4-beta-xylanase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.1.8 3.2.1.8] Structure known Active Site: CA1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1GMM OCA].  

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