Glutamine 666 renders murine ADAM10 an inefficient S.aureus alpha-toxin receptor

Abstract

S. aureus is one of the most important causes of infectious diseases in hospitalized individuals and outpatients. The majority of clinical isolates secretes large amounts of the small membrane pore-forming -toxin, alias -hemolysin, which serves as an important virulence factor of this organism. The identification of A Disintegrin And Metalloprotease (ADAM10) as its high affinity receptor held great promise for a better understanding of the processes underlying membrane damage by -toxin. Twelve years on however, the molecular details of initial toxin binding to target cells remain elusive. Because we noted that several murine cell lines were resilient to -toxin, we considered the possibility that murine ADAM10 could be less efficient a receptor, as compared to human or bovine orthologues. Accordingly, we sought to identify amino acid residues in ADAM10, which could explain species-dependent functionality as receptor for -toxin. Our work led to the finding that replacement of a single glutamine residue (Q666) in murine ADAM10 with corresponding glutamic acid (E665) of human or bovine ADAM10 enhances significantly the binding and consequent cytotoxicity of -toxin. Consistently, a synthetic peptide comprising E665 mitigated -toxin-dependent hemolysis. In multicellular organisms, E665 is highly conserved, but mice and several other members of the taxon glires evolved glutamine at the corresponding position. The residue is located in a short membrane proximal, extracellular region of ADAM10. Taken together, available structural information, in silico docking, and functional data suggests that -toxin monomers could bind to cellular membranes via this so-called stalk region of ADAM10 and phosphocholine.