2bem: Difference between revisions

Chitin proteins are commonly found in bacteria that utilize chitin as a, source of energy. CBP21 is a chitin-binding protein from Serratia, marcescens, a Gram-negative soil bacterium capable of efficient chitin, degradation. When grown on chitin, S. marcescens secretes large amounts of, CBP21, along with chitin-degrading enzymes. In an attempt to understand, the molecular mechanism of CBP21 action, we have determined its crystal, structure at 1.55 angstroms resolution. This is the first structure to be, solved of a family 33 carbohydrate-binding module. The structure reveals a, "budded" fibronectin type III fold consisting of two beta-sheets, arranged, as a beta-sheet sandwich, with a 65-residue "bud" consisting of three, short helices, located between beta-strands 1 and 2. Remarkably, conserved, aromatic residues that have been suggested previously to play a role in, chitin binding were mainly found in the interior of the protein, seemingly, incapable of interacting with chitin, whereas the structure revealed a, surface patch of highly conserved, mainly hydrophilic residues. The roles, of six of these conserved surface-exposed residues (Tyr-54, Glu-55, Glu-60, His-114, Asp-182, and Asn-185) were probed by site-directed, mutagenesis and subsequent binding studies. All single point mutations, lowered the affinity of CBP21 for beta-chitin, as shown by 3-8-fold, increases in the apparent binding constant. Thus, binding of CBP21 to, chitin seems to be mediated primarily by conserved, solvent-exposed, polar, side chains.

2BEM is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Serratia_marcescens Serratia marcescens] with SO4, NA and EDO as [http://en.wikipedia.org/wiki/ligands ligands]. Structure known Active Site: AC1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=2BEM OCA].  

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