Salivary antigen‐5/CAP family members are Cu 2+ ‐dependent antioxidant enzymes which negatively modulate platelet function

The function of the antigen‐5/CAP family of salivary gland (SG) proteins ubiquitously found in bloodsucking animals has remained elusive for decades. Antigen 5 members from the hematophagous bugs Dipetalogaster maxima (DMAV) and Triatoma infestans (TIAV) were expressed and discovered to attenuate platelet aggregation by low doses of collagen (<1 μg/mL) but no other agonists. This inhibitory profile resembles the effects of antioxidants (e.g., superoxide dismutase [SOD]) in platelet function. Accordingly, our results demonstrate that DMAV blunts the luminescence signal of O 2 − generated by phorbol myristate acetate (PMA)‐stimulated neutrophils. Moreover, Cu 2+ ‐DMAV was found to inhibit cytochrome c reduction by O 2 − generated by the xanthine/xanthine oxidase implying that it exhibits antioxidant activity. Mechanistically, ICP‐MS and fluorescence spectroscopy revealed that DMAV, like SOD, interacts with Cu 2+ which provides redox potential for catalytic removal of O 2 − . Notably, SG of D. maxima with native DMAV contain Cu 2+ and display metal‐dependent antioxidant properties. Antigen‐5/CAP emerges as a novel family of Cu 2+ ‐dependent antioxidant enzymes that negatively modulate platelet aggregation by a unique salivary mechanism.