Characterization of genes from Thermoanaerobacterium thermosulfurigenes EM1 that encode two glycosyl hydrolases with conserved S-layer-like domains

Two genes from Thermoanaerobacterium thermosulfurigenes EM1 were identified which are predicted to encode a xylanase (XynA) and a polygalacturonate hydrolase (PglA). The xynA gene has the potential to encode a 1234-amino acid product consisting of a signal peptide followed by a repeated domain, a xylanase family F domain, two cellulose-binding domains and a triplicated sequence at its C-terminus. The gene pglA is predicted to encode a product of 1148 amino acids consisting of a signal sequence followed by a fibronectin type III-like domain (Fn3 domain), the catalytic domain, a Gly/Thr/Ser/Asn-rich segment and a triplicated domain. The triplicated segments at the C-termini of deduced XynA and PglA are about 95% identical to each other and to the S-layer-like domains of the previously characterized pullulanase (AmyB) from the same organism. In contrast, sequence comparisons revealed only distant amino acid sequence similarities between the fibronectin type III-like domains of PglA and AmyB from T. thermosulfurigenes EM1.