Three multidomain esterases from the cellulolytic rumen anaerobe Ruminococcus flavefaciens 17 that carry divergent dockerin sequences

Three enzymes carrying esterase domains have been identified in the rumen c ellulolytic anaerobe Ruminococcus flavefaciens 17, The newly characterized CesA gene product (768 amino acids) includes an N-terminal acetylesterase d omain and an unidentified C-terminal domain, while the previously character ized XynB enzyme (781 amino acids) includes an internal acetylesterase doma in in addition to its N-terminal xylanase catalytic domain. A third gene, x ynE, is predicted to encode a multidomain enzyme of 792 amino acids includi ng a family 11 xylanase domain and a C-terminal esterase domain. The estera se domains from CesA and XynB share significant sequence identity (44%) and belong to carbohydrate esterase family 3; both domains are shown here to b e capable of deacetylating acetylated xylans, but no evidence was found for ferulic acid esterase activity. The esterase domain of XynE, however, shar es 42 % amino acid identity with a family 1 phenolic acid esterase domain i dentified from Clostridum thermocellum XynZ, XynB, XynE and CesA all contai n dockerin-like regions in addition to their catalytic domains, suggesting that these enzymes form part of a cellulosome-like multienzyme complex. The dockerin sequences of CesA and XynE differ significantly from those previo usly described in R, flavefaciens polysaccharidases, including XynB, sugges ting that they might represent distinct dockerin specificities.