These repeats are characterised by conserved aromatic residues and glycines are found in multiple tandem copies in a number of proteins. The CW repeat is 20 amino acid residues long. The exact domain boundaries may not be correct. It has been suggested that these repeats in Swiss:P15057 might be responsible for the specific recognition of choline-containing cell walls [1]. Similar but longer repeats are found in the glucosyltransferases and glucan-binding proteins of oral streptococci and shown to be involved in glucan binding [2] as well as in the related dextransucrases of Leuconostoc mesenteroides. Repeats also occur in toxins of Clostridium difficile and other clostridia, though the ligands are not always known.

1: Molecular evolution of lytic enzymes of Streptococcus pneumoniae and its bacteriophages. Garcia E, Garcia JL, Garcia P, Arraras A, Sanchez-Puelles JM, Lopez R; Proc Natl Acad Sci U S A 1988;85:914-918. PMID:3422470

2: Structural basis for selective recognition of pneumococcal cell wall by modular endolysin from phage Cp-1. Hermoso JA, Monterroso B, Albert A, Galan B, Ahrazem O, Garcia P, Martinez-Ripoll M, Garcia JL, Menendez M; Structure (Camb) 2003;11:1239-1249. PMID:14527392

3: Tracking the evolution of the bacterial choline-binding domain: molecular characterization of the Clostridium acetobutylicum NCIB 8052 cspA gene. Sanchez-Beato AR, Ronda C, Garcia JL; J Bacteriol 1995;177:1098-1103. PMID:7860591

4: A family of clostridial and streptococcal ligand-binding proteins with conserved C-terminal repeat sequences. Wren BW; Mol Microbiol 1991;5:797-803. PMID:1830357

5: Sequence analysis of the gene for the glucan-binding protein of Streptococcus mutans Ingbritt. Banas JA, Russell RR, Ferretti JJ; Infect Immun 1990;58:667-673. PMID:2307516

6: Nucleotide sequence of a glucosyltransferase gene from Streptococcus sobrinus MFe28. Ferretti JJ, Gilpin ML, Russell RR; J Bacteriol 1987;169:4271-4278. PMID:3040686

7: Location of repeat elements in glucansucrases of Leuconostoc and Streptococcus species. Janecek S, Svensson B, Russell RR; FEMS Microbiol Lett 2000;192:53-57. PMID:11040428