Sequencing and expression of additional xylanase genes from the hyperthermophile Thermotoga maritima FjSS3B.1

Two genes, xynB and xynC, coding for xylanases were isolated from Thermotog a maritima FjSS3B.1 by a genomic-walking-PCR technique. Sequencing of the g enes showed that they encode multidomain family 10 xylanases. Only XynB exh ibited activity against xylan substrates, The temperature optimum (87 degre es C) and pH optimum (pH 6.5) of XynB are different from the previously rep orted xylanase, XynA. (also a family 10 enzyme), from this organism. The ca talytic domain expressed without other domains has a lower temperature opti mum, is less thermostable, and has optimal activity at pH 6.5. Despite havi ng a high level of sequence similarity to xynB, xynC appears to be nonfunct ional since its encoded protein did not show significant activity on xylan substrates.