1us2: Difference between revisions

Microbial degradation of the plant cell wall is the primary mechanism by, which carbon is utilized in the biosphere. The hydrolysis of xylan, by, endo-beta-1,4-xylanases (xylanases), is one of the key reactions in this, process. Although amino acid sequence variations are evident in the, substrate binding cleft of "family GH10" xylanases (see, afmb.cnrs-mrs.fr/CAZY/), their biochemical significance is unclear. The, Cellvibrio japonicus GH10 xylanase CjXyn10C is a bi-modular enzyme, comprising a GH10 catalytic module and a family 15 carbohydrate-binding, module. The three-dimensional structure at 1.85 A, presented here, shows, that the sequence joining the two modules is disordered, confirming that, linker sequences in modular glycoside hydrolases are highly flexible., CjXyn10C hydrolyzes xylan at a rate similar to other previously described, GH10 enzymes but displays very low activity against xylooligosaccharides., The poor activity on short substrates reflects weak binding at the -2, subsite of the enzyme. Comparison of CjXyn10C with other family GH10, enzymes reveals "polymorphisms" in the substrate binding cleft including a, glutamate/glycine substitution at the -2 subsite and a tyrosine insertion, in the -2/-3 glycone region of the substrate binding cleft, both of which, contribute to the unusual properties of the enzyme. The CjXyn10C-substrate, complex shows that Tyr-340 stacks against the xylose residue located at, the -3 subsite, and the properties of Y340A support the view that this, tyrosine plays a pivotal role in substrate binding at this location. The, generic importance of using CjXyn10C as a template in predicting the, biochemical properties of GH10 xylanases is discussed.

1US2 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Cellvibrio_japonicus Cellvibrio japonicus]. 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: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1US2 OCA].  

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