Identification of a region responsible for binding to the cell wall within the S-layer protein of Clostridium thermocellum

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Abstract
Summary: The protomer forming the S-layer of Clostridium thermocellum was identified as a 140 kDa protein which was non-covalently bound to the cell wall. Cloning and sequencing of the corresponding gene revealed an open reading frame of 3108 nucleotides encoding a polypeptide of 1036 amino acids, termed SIpA. The amino acid composition of SIpA matches the composition of a previously described exocellular glycoprotein. SIpA shared extensive similarity with the S-layer protein of Bacillus sphaericus and with the outer wall protein of Bacillus brevis. In addition, the amino-terminal region of SIpA contained a segment presenting similarities with segments termed SLH (S-layer homologous), which are found in several bacterial exoproteins. A polypeptide of 209 residues comprising this segment was shown to bind to cell walls extracted from C. thermocellum cells.