Genetic Analysis of Bifunctional Genes from Rumen Bacterium

摘要

Deletion of domain B of the xynD gene was performed and the nucleotide sequence of this domain was compared with other enzyme sequences to reveal its function. Ruminococcus flavefaciens DNA fragment encodes xylanase and β-(1,3-1,4)-glucanase (xynD) activities with 3 domains (A, B, C). The amino-terminal domain (A) is related to family G xylanase while the carboxy-terminal domain (C) is related to family 16 β-(1,3-1,4)-glucanase. These 2 domains are connected by a region (B) of unknown function. Deletion of domain B leads to increased thermosensitivity of the enzyme and also in a 2-3-fold increase in β-(1,3-1,4)-glucanase activity. A survey of the available sequence databases revealed the presence of thermostabilizing domains in numerous other enzymes from various organisms. Although this domain has thermostabilizing properties, it has been proved that similar sequences of non-catalytic domains from other sources also showed xylan binding properties. Therefore, these domains are also called xylan binding domains (XBDs).