Streptococcus pyogenes is one of the most common human pathogens and possesses diverse mechanisms to evade the human immune defence. One example of its immune evasion is the degradation of the
chemokine IL (interleukin)-8 by ScpC, a
serine proteinase that prevents the recruitment of neutrophils to an
infection site. By applying the ANTIGENome technology and using human serum
antibodies, we identified Spy0416, annotated as ScpC, as a prominent
antigen that induces protective immune responses in animals. We demonstrate here for the first time that the recombinant form of Spy0416 is capable of
IL-8 degradation in vitro in a concentration- and time-dependent manner. Mutations in the conserved
amino acid residues of the catalytic triad of Spy0416 completely abolished in vitro activity. However, the isolated predicted
proteinase domain does not exhibit IL-8-degrading activity, but is dependent on the presence of the C-terminal region of Spy0416. Binding to
IL-8 is mainly mediated by the catalytic domain. However, the C-terminal region modulates substrate binding, indicating that the proteolytic activity is amenable to regulation via the non-catalytic regions. The specificity for human substrates is not restricted to
IL-8, since we also detected in vitro
protease activity for another
CXC chemokine GRO-alpha (growth-related oncogene alpha), but not for NAP-2 (neutrophil-activating
protein 2), SDF (stromal-cell-derived factor)-1alpha, PF-4 (
platelet factor 4), I-TAC (
interferon-gamma-inducible T-cell alpha-
chemoattractant), IP-10 (interferon-gamma-inducible protein 10) and MCP-1 (
monocyte chemoattractant protein 1). The degradation of two human
CXC chemokines in vitro, the high sequence conservation, the immunogenicity of the
protein in humans and the shown protection in animal studies suggest that Spy0416 is a promising
vaccine candidate for the prevention of
infections by S. pyogenes.