DOCKERIN-LIKE SEQUENCES IN CELLULASES AND XYLANASES FROM THE RUMEN CELLULOLYTIC BACTERIUM RUMINOCOCCUS-FLAVEFACIENS

Recent analysis of the endA cellulase gene from Ruminococcus flavefaci ens 17 has revealed that it encodes a product of 759 amino acids that provides the first example of a multidomain cellulase from a Ruminococ cus sp. Following the family 5 catalytic domain in the predicted EndA enzyme is a 282 amino acid domain of unknown function for which no clo se relationship was found to other protein sequences. However, the C-t erminal sequences of EndA contain a 34 amino acid threonine-rich linke r connected to an 81 amino acid region, both of which show strong simi larities to sequences present in two xylanases from ii. flavefaciens 1 7. A distant relationship is evident between regions of the 80 amino a cid sequences of EndA, XynD and XynB and the duplicated 23 amino acid dockerin sequences found in cellulolytic Clostridium sp., suggesting t hat as in Clostridium sp. these sequences could mediate the binding of enzymatic polypeptides to another component in the cell surface enzym e complex of R. flavefaciens.