Functional dissection of Streptococcus pyogenes M5 protein: the hypervariable region is essential for virulence

• Published in: PloS one 2009-10, Vol.4 (10), p.e7279-e7279
• Main Authors: Waldemarsson, Johan, Stålhammar-Carlemalm, Margaretha, Sandin, Charlotta, Castellino, Francis J, Lindahl, Gunnar
• Format: Article
• Language: English
• Subjects: Analysis; Animals; Antigens, Bacterial - chemistry; Attenuation; Bacteria; Bacterial Outer Membrane Proteins - chemistry; Basic Medicine; Binding; Biochemistry; Carrier Proteins - chemistry; Cell adhesion & migration; Chromatography, Affinity - methods; Complementarity Determining Regions - immunology; Dissection; Female; Fibrin; Fibrinogen; Fibrinogen - chemistry; Health aspects; Humans; Immunoglobulins; Immunology/Immunity to Infections; Infection; Infections; Infectious Diseases/Bacterial Infections; Laboratories; Ligands; M protein; Male; Medical and Health Sciences; Medicin och hälsovetenskap; Medicine; Medicinska och farmaceutiska grundvetenskaper; Mice; Mice, Inbred BALB C; Mice, Inbred C3H; Mice, Inbred C57BL; Microbiology in the medical area; Microbiology/Cellular Microbiology and Pathogenesis; Mikrobiologi inom det medicinska området; Mixed infection; Mutants; Pathogens; Pediatrics; Phagocytosis; Protein Binding; Protein Structure, Tertiary; Proteins; Streptococcus; Streptococcus infections; Streptococcus pyogenes; Streptococcus pyogenes - immunology; Streptococcus pyogenes - metabolism; Studies; Surgery; Surveillance; Virulence; Virulence (Microbiology); Virulence factors
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0007279

The surface-localized M protein of Streptococcus pyogenes is a major virulence factor that inhibits phagocytosis, as determined ex vivo. Because little is known about the role of M protein in vivo we analyzed the contribution of different M protein regions to virulence, using the fibrinogen (Fg)-binding M5 protein and a mouse model of acute invasive infection. This model was suitable, because M5 is required for mouse virulence and binds mouse and human Fg equally well, as shown here. Mixed infection experiments with wild type bacteria demonstrated that mutants lacking the N-terminal hypervariable region (HVR) or the Fg-binding B-repeat region were strongly attenuated, while a mutant lacking the conserved C-repeats was only slightly attenuated. Because the HVR of M5 is not required for phagocytosis resistance, our data imply that this HVR plays a major but unknown role during acute infection. The B-repeat region is required for phagocytosis resistance and specifically binds Fg, suggesting that it promotes virulence by binding Fg. However, B-repeat mutants were attenuated even in Fg-deficient mice, implying that the B-repeats may have a second function, in addition to Fg-binding. These data demonstrate that two distinct M5 regions, including the HVR, are essential to virulence during the early stages of an infection. In particular, our data provide the first in vivo evidence that the HVR of an M protein plays a major role in virulence, focusing interest on the molecular role of this region.