Abstract
Staphylococcus aureus expresses various surface proteins which specifically recognize and bind to different host molecules. We have previously identified a bacterial protein that exhibits a broad specificity and binds to several mammalian extracellular proteins. The gene encoding this bacterial component has now been cloned and sequenced. The deduced protein consists predominantly of six repeated domains of 110 residues. Each of the repeated domains contain a subdomain of 31 residues that share striking sequence homology with a segment in the peptide binding groove of the beta chain of the major histocompatibility complex (MHC) class II proteins from different mammalian species. The purified recombinant bacterial protein bound several mammalian proteins, including recombinant osteopontin, suggesting a protein-protein interaction and also specifically recognized a 15-amino acid residue synthetic peptide. Taken together, these results suggest that the bacterial protein resembles mammalian MHC class II molecules with respect to both sequence similarities and peptide binding capabilities.
Highlights
Pathogenic bacteria have evolved in close association with their hosts and have developed sophisticated mechanisms to increase their chances of survival
These include exotoxins, exoenzymes, and a family of specific protein adhesins (MSCRAMMs) that mediate the adherence of the organism to host tissues and extracellular matrix components (4 – 6). Some of these adhesins have been characterized in molecular detail, including the fibronectin adhesins (FnBPA and FnBPB), the collagen adhesin (Cna), and the fibrinogen adhesin
Site-specific mutants have been isolated and compared with parental strains in both in vitro and in vivo models of adherence and infection, and there is significant evidence that each of these adhesins is an important determinant for colonization and virulence (5, 6). These proteins have similar features, including a signal peptide at the NH2 terminus and at the COOH terminus, an LPXTG motif preceding a hydrophobic membrane spanning region, and a positively charged tail, which are involved in anchoring the proteins in the cell wall
Summary
Pathogenic bacteria have evolved in close association with their hosts and have developed sophisticated mechanisms to increase their chances of survival. The deduced protein contains repeated subdomains that share striking sequence homology with a segment of the peptide binding groove of the  chain of MHC class II mammalian proteins. We have designated the protein as Map (MHC class II analogous protein) and demonstrated that the purified recombinant bacterial protein recognizes a 15-amino acid residue synthetic peptide derived from vitronectin.
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