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Publication Abstract from PubMed

The microbial degradation of lignocellulose biomass is not only an important biological process but is of increasing industrial significance in the bioenergy sector. The mechanism by which the plant cell wall, an insoluble composite structure, activates the extensive repertoire of microbial hydrolytic enzymes required to catalyse its degradation is poorly understood. Here we have used a transposon mutagenesis strategy to identify a genetic locus, consisting of two genes that modulate the expression of xylan-side chain degrading enzymes in the saprophytic bacterium Cellvibrio japonicus. Significantly the locus encodes a two-component signalling system, designated AbfS (sensor histidine kinase) and AbfR (response regulator). The AbfR/S two-component system is required to activate the expression of the suite of enzymes that remove the numerous side chains from xylan, but not the xylanases which hydrolyse the 1,4-linkedxylose polymeric backbone of this polysaccharide. Studies on the recombinant sensor domain of AbfS (AbfSSD) showed that it bound to decorated xylans and arabinoxylooligosaccharides, but not to undecorated xylooligosaccharides or other plant structural polysaccharides/oligosaccharides. The crystal structure of AbfSSD was determined to a resolution of 2.6 A. The overall fold of AbfSSD is that of a classical PAS domain with a central antiparallel four-stranded -sheet flanked by -helices. Our data expand the number of molecules known to bind to the sensor domain of two-component histidine kinases to include complex carbohydrates. The biological rationale for a regulatory system that induces enzymes that remove the side chains of xylan, but not the hydrolases that cleave the backbone of the polysaccharide, is discussed.

Regulation of the xylan degrading apparatus of Cellvibrio japonicus by a novel two-component system.,Emami K, Topakas E, Nagy T, Henshaw J, Jackson KA, Nelson KE, Mongodin EF, Murray JW, Lewis RJ, Gilbert HJ J Biol Chem. 2008 Oct 15. PMID:18922794^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.