IDENTIFICATION OF A REGION RESPONSIBLE FOR BINDING TO THE CELL-WALL WITHIN THE S-LAYER PROTEIN OF CLOSTRIDIUM-THERMOCELLUM

The protomer forming the S-layer of Clostridium thermocellum was ident ified as a 140 kDa protein which was non-covalently bound to the cell wall. Cloning and sequencing of the corresponding gene revealed an ope n reading frame of 3108 nucleotides encoding a polypeptide of 1036 ami no acids. termed SlpA. The amino acid composition of SlpA matches the composition of a previously described exocellular glycoprotein. SlpA s hared extensive similarity with the S-layer protein of Bacillus sphaer icus and with the outer wall protein of Bacillus brevis. In addition, the amino-terminal region of SlpA contained a segment presenting simil arities with segments termed SLH (S-layer homologous), which are found in several bacterial exoproteins. A polypeptide of 209 residues compr ising this segment was shown to bind to cell walls extracted from C. t hermocellum cells.