Amblyomma americanum tick saliva serine protease inhibitor 6 is a cross‐class inhibitor of serine proteases and papain‐like cysteine proteases that delays plasma clotting and inhibits platelet aggregation. Issue 3 (24th March 2013)

• Record Type: Journal Article
• Authors: Mulenga, A.; Kim, T.; Ibelli, A. M. G.
• Is Part Of: Insect molecular biology. Volume 22:Issue 3(2013:Jun.)
• Page Start: 306
• Page End: 319
• Publication Date: 2013-03-24
• Subjects: Insects -- Molecular aspects -- Periodicals; 595.7
• DOI: 10.1111/imb.12024
• Languages: English
• ISSNs: 0962-1075

Abstract

<abstract abstract-type="main"> <title>Abstract</title> <p>We previously demonstrated that <italic>A</italic><italic>mblyomma americanum</italic> tick serine protease inhibitor 6 (<italic>Aam</italic>S6) was secreted into the host during tick feeding and that both its mRNA and protein were ubiquitously and highly expressed during the first 3 days of tick feeding. This study demonstrates that <italic>A</italic><italic>am</italic>S6 is a cross‐class inhibitor of both serine‐ and papain‐like cysteine proteases that has apparent antihaemostatic functions. Consistent with the typical inhibitory serpin characteristics, enzyme kinetics analyses revealed that <italic>Pichia pastoris‐</italic>expressed recombinant (r) <italic>A</italic><italic>am</italic>S6 reduced initial velocities of substrate hydrolysis (<italic>V</italic><sub>0</sub>) and/or maximum enzyme velocity (<italic>V</italic><sub>max</sub>) of trypsin, chymotrypsin, elastase, chymase, and papain in a dose–response manner. We speculate that r<italic>A</italic><italic>am</italic>S6 inhibited plasmin in a temporary fashion in that while r<italic>A</italic><italic>am</italic>S6 reduced <italic>V</italic><sub>0</sub> of plasmin by up to ∼53%, it had no effect on <italic>V</italic><sub>max</sub>. Our data also suggest that r<italic>Am</italic>S6 has minimal or no apparent effect on <italic>V</italic><sub>0</sub> or <italic>V</italic><sub>max</sub> of thrombin, factor Xa, and kallikrein. We speculate that <italic>Aam</italic>S6 is apparently involved in facilitating blood meal feeding in that various amounts of r<italic>A</italic><italic>am</italic>S6 reduced platelet aggregation by up to ∼47% and delayed plasma clotting time in the recalcification time assay by up to ∼210 s. <italic>A</italic><italic>am</italic>S6 is most likely not involved with the tick's evasion of the host's complement defense mechanism, in that r<italic>A</italic><italic>am</italic>S6 did not interfere with the complement activation pathway. Findings in this study are discussed in the context of expanding our understanding of tick proteins that control bloodmeal feeding and hence tick‐borne disease transmission by ticks.</p> </abstract>