Molecular cloning and expression of the gene for elastin-binding protein (ebpS) in Staphylococcus aureus

Interactions between staphylococci and components of the extracellular matrix mediate attachment of the bacteria to host tissues and organs and define an important mechanism leading to colonization, invasion, and formation of metastatic abscesses. We have previously demonstrated a specific binding interaction between Staphylococcus aureus and elastin, one of the major protein components of the extracellular matrix. Available evidence suggests that this association is mediated by a 25-kDa elastin-binding protein on the surface of S. aureus (EbpS). To study the molecular structure and function of EbpS, the gene encoding EbpS was cloned, sequenced, and expressed in Escherichia coli. DNA sequence data indicate that the ebpS open reading frame consists of 606 base pairs and encodes a novel polypeptide with a predicted molecular mass of 23,345 daltons and pI of 4.9. A polyclonal antibody raised against recombinant EbpS interacted with the native 25-kDa cell surface EbpS and inhibited staphylococcal elastin binding. Furthermore, recombinant EbpS bound specifically to immobilized elastin and inhibited binding of S. aureus to elastin. A degradation product of recombinant EbpS lacking the first 59 amino acids of the molecule and a C-terminal fragment of CNBr-cleaved recombinant EbpS, however, did not interact with elastin. Together, these results confirm that EbpS is the cell surface molecule mediating binding of S. aureus to elastin. The inability of truncated forms of recombinant EbpS to bind to elastin suggests that the elastin binding site in EbpS is contained in the first 59 amino acids of the molecule.