Protein Family Models

This family consists exclusively of streptococcal competence stimulating peptide precursors, which are generally up to 50 amino acid residues long. In all the members of this family, the leader sequence is cleaved after two conserved glycine residues; thus the leader sequence is of the double- glycine type [2]. Competence stimulating peptides (CSP) are small (less than 25 amino acid residues) cationic peptides. The N-terminal amino acid residue is negatively charged, either glutamate or aspartate. The C-terminal end is positively charged. The third residue is also positively charged: a highly conserved arginine [2]. A few COMC proteins and their precursors (not included in this family) do not fully follow the above description. In particular: the leader sequence in the CSP precursor from Streptococcus sanguis NCTC 7863 Swiss:O33758 is not of the double-glycine type; the CSP from Streptococcus gordonii NCTC 3165 Swiss:O33645 does not have a negatively charged N-terminus residue and has a lysine instead of arginine at the third position. Functionally, CSP act as pheromones, stimulating competence for genetic transformation in streptococci. In streptococci, the (CSP mediated) competence response requires exponential cell growth at a critical density, a relatively simple requirement when compared to the stationary-phase requirement of Haemophilus, or the late-logarithmic- phase of Bacillus [1]. All bacteria induced to competence by a particular CSP are said to belong to the same pherotype, because each CSP is recognised by a specific receptor (the signalling domain of a histidine kinase ComD). Pherotypes are not necessarily s. TRUNCATED at 1650 bytes (from Pfam)

Date:

2024-08-14