Identification of non-catalytic conserved regions in xylanases encoded by the xynB and xynD genes of the cellulolytic rumen anaerobe Ruminococcus flavefaciens |
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Authors: | Jun-Xian Zhang Jennifer Martin Harry J. Flint |
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Affiliation: | 1. Rowett Research Institute, Greenburn Road, A132 9SB, Bucksburn, Aberdeen, UK
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Abstract: | xynB is one of at least four genes from the cellulolytic rumen anaerobe Ruminococcus flavefaciens 17 that encode xylanase activity. The xynB gene is predicted to encode a 781-amino acid product starting with a signal peptide, followed by an amino-terminal xylanase domain which is identical at 89% and 78% of residues, respectively, to the amino-terminal xylanase domains of the bifunctional XynD and XynA enzymes from the same organism. Two separate regions within the carboxy-terminal 537 amino acids of XynB also show close similarities with domain B of XynD. These regions show no significant homology with cellulose- or xylan-binding domains from other species, or with any other sequences, and their functions are unknown. In addition a 30 to 32-residue threonine-rich region is present in both XynD and XynB. Codon usage shows a consistent pattern of bias in the three xylanase genes from R. flavefaciens that have been sequenced. |
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