Location of the complement factor H binding site on streptococcal M6 protein.
The surface M protein of group A streptococci binds factor H, a regulatory protein of the alternative complement pathway, which may contribute to the antiphagocytic activity of the M molecules. To locate the factor H binding domain in the alpha-helical coiled-coil structure of the M molecule, the M protein was cleaved with pepsin at pH 5.8, which separates the molecule approximately in half. Western blot (immunoblot), amino acid sequence, and mass spectrometric analyses revealed that factor H bound to a 14.6-kDa C-terminal fragment of the M molecule. Competitive inhibition of factor H binding to the 14.6-kDa fragment with M protein peptides localized the binding site to amino acids 256 to 292. This segment is located within the surface-exposed region of the M6 protein, identified as the C-repeat region, whose sequence is conserved among heterologous M and M-like molecules. These studies also identified a second pepsin-susceptible site with the sequence ELAK located within the cell wall-associated region of the M molecule.
Fischetti
V A
VA
Laboratory of Bacterial Pathogenesis and Immunology, Rockefeller University, New York, New York 10021.
Horstmann
R D
RD
Pancholi
V
V
D000595:Amino Acid Sequence; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000378:metabolism*; D002352:Carrier Proteins; D017242:Complement Factor H / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D008565:Membrane Proteins; D010446:Peptide Fragments; C014689:streptococcal M protein; D017242:Complement Factor H