Molecular characterization of a family of choline-binding proteins of Clostridium beijerinckii NCIB 8052. Evolution and gene redundancy in prokaryotic cell.

Three genes homologous to cspA, which encodes the major secretable protein of Clostridium beijerinckii NCIB 8052 have been cloned and sequenced. The Csp proteins showed the typical modular structure of cell-wall associated proteins and, that found in the choline-binding proteins of Streptococcus pneumoniae. The variable number of repeats that constitute the C-terminal choline-binding domain suggests that the csp genes have evolved by deletion-duplication events. Northern blot analysis indicated that under the culture conditions employed only two genes, cspA and cspC, are efficiently expressed and their products are detected in the culture medium. The csp genes are not contiguously located in the chromosome and appear to be expressed independently. Primer extension experiments located a transcription start site 29 bp upstream of the cspA initiation codon. The -10 and -35 promoter regions are closely related to the consensus sequence of Escherichia coli sigma 70 promoters. The cell wall binding capacity of the clostridial proteins, their abundance in the extracellular media, together with the existence of gene redundancy suggest that the Csp proteins should play an important role in the interaction of this microorganism with its surrounding environment.