Family 10 and 11 xylanase genes from Caldicellulosiruptor sp strain Rt69B.1

Three family 10 xylanase genes (xynA, xynB, and xynC) and a single family 1 1 xylanase gene (xynD) were identified from the extreme thermophile Caldice llulosiruptor strain Rt69B.1 through the use of consensus PCR in conjunctio n with sequencing and polyacrylamide gel electrophoresis. These genes appea r to comprise the complete endoxylanase system of Rt69B.1. The xynA gene wa s found to be homologous to the xynA gene of the closely related Caldicellu losiruptor strain Rt8B.4, and primers designed previously to amplify the Rt 8B.4 xynA gene could amplify homologous full-length xynA gene fragments fro m Rt69B.1. The complete nucleotide sequences of the Rt69B.1 xynB, xynC, and xynD genes were obtained using genomic walking PCR. The full-length xynB a nd xynC genes are more than 5 kb in length and encode highly modular enzyme s that are the largest xylanases reported to date. XynB has an architecture similar to the family 10 xylanases from Thermoanaerobacterium saccharolyti cum (XynA) and Clostridium thermocellum (XynX) and may be cell wall associa ted, while XynC is a bifunctional enzyme with an architecture similar to th e bifunctional beta-glycanases from Caldicellulosiruptor saccharolyticus. T he xynD gene encodes a two-domain family 11 xylanase that is identical in a rchitecture to the XynB family 11 xylanase from the unrelated extreme therm ophile Dictyoglomus thermophilum strain Rt46B.1. The sequence similarities between the Rt69B.1 xylanases with respect to their evolution are discussed .