Identification and characterization of a second extracellular collagen-like protein made by group A Streptococcus: Control of production at the levelof translation

A recent study found that group A Streptococcus (GAS) expresses a cell surf ace protein with similarity to human collagen (S, Lukomski, K. Nakashima, I . Abdi, V, J, Cipriano, R. M, Ireland, S. R, Reid, G, G, Adams, and J, M. M usser, Infect. Immun, 68:6542-6553, 2000), This streptococcal collagen-like protein (Scl) contains a long region of Gly-X-X motifs and was produced by serotype M1 GAS strains. In the present study, a second member of the scl gene family was identified and designated scl2. The Scl2 protein also has a collagen-like region, which in M1 strains is composed of 38 contiguous Gly X-X triplet motifs, The scl2 gene was present in all 50 genetically divers e GAS strains studied. The Scl2 protein is highly polymorphic, and the numb er of Gly-X-X motifs in the 50 strains studied ranged from 31 in one seroty pe M1 strain to 79 in serotype M28 and M77 isolates. The scl1 and scl2 gene s were simultaneously transcribed in the exponential phase, and the Sd prot eins were also produced. Scl1 and Scl2 were identified in a cell-associated form and free in culture supernatants, Production of Scl1 is regulated by Mga, a positive transcriptional regulator that controls expression of sever al GAS virulence factors. In contrast, production of Scl2 is controlled at the level of translation by variation in the number of short-sequence penta nucleotide repeats (CAAAA) located immediately downstream of the GTG (Val) start codon. Control of protein production by this molecular mechanism has not been identified previously in GAS. Together, the data indicate that GAS simultaneously produces two extracellular human collagen-like proteins in a regulated fashion.