Premium
A mblyomma 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
Author(s) -
Mulenga A.,
Kim T.,
Ibelli A. M. G.
Publication year - 2013
Publication title -
insect molecular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.955
H-Index - 93
eISSN - 1365-2583
pISSN - 0962-1075
DOI - 10.1111/imb.12024
Subject(s) - proteases , biology , kallikrein , biochemistry , plasmin , serpin , serine protease , serine , kunitz sti protease inhibitor , amblyomma americanum , protease , microbiology and biotechnology , enzyme , tick , virology , ixodidae , gene
We previously demonstrated that A mblyomma americanum tick serine protease inhibitor 6 ( Aam S6 ) was secreted into the host during tick feeding and that both its m RNA and protein were ubiquitously and highly expressed during the first 3 days of tick feeding. This study demonstrates that A am S 6 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 P ichia pastoris‐ expressed recombinant (r) A am S 6 reduced initial velocities of substrate hydrolysis ( V 0 ) and/or maximum enzyme velocity ( V max ) of trypsin, chymotrypsin, elastase, chymase, and papain in a dose–response manner. We speculate that r A am S 6 inhibited plasmin in a temporary fashion in that while r A am S 6 reduced V 0 of plasmin by up to ∼53%, it had no effect on V max . Our data also suggest that r Am S6 has minimal or no apparent effect on V 0 or V max of thrombin, factor X a, and kallikrein. We speculate that Aam S6 is apparently involved in facilitating blood meal feeding in that various amounts of r A am S 6 reduced platelet aggregation by up to ∼47% and delayed plasma clotting time in the recalcification time assay by up to ∼210 s. A am S 6 is most likely not involved with the tick's evasion of the host's complement defense mechanism, in that r A am S 6 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.