ИСТИНА

The red king crab, P. camtschaticus, is a large commercially important crustacean in Russia, Norway, and the US, with annual landings estimated in the range of tens of millions of kgs. Previously, from the P. camtschaticus we isolated a serpin (further serpin PC), which had an anticoagulant and an anticomplement effects on the human blood. Based on its action we hypothesized its role in host’s immunity since these proteins were reported to be engaged in defense systems of other crustaceans, are highly homologous, and there is still a lack of valuable biochemical data on their exact role, partner peptidases, and specificity. Recombinant serpin PC’s reactivity was previously tested towards various serine and cysteine proteases, and it was found that it inhibits a bovine cationic trypsin, the reaction proceeds through the characteristic serpin mechanism, with the unusual reaction site. After we proved its inhibitory function on the model partner peptidase, we decided to find whether it performs as the inhibitor in a host organism and clarify its function. Earlier we found that its highest level of transcription is in the hemocytes, and, due to the presence of the secretion signal, it can be secreted to the hemolymph. Thus, we performed a peptidase activity profiling of hemocytes and plasma with the recombinant serpin PC and other peptidase inhibitors, and found that it inhibits at least two R/K-specific activities. In arthropods, hemocyte serpins are known to regulate the melanization cascade, that involves a number of peptidases of aforementioned specificity, therefore we further assessed serpin PC’s effect on its activation. We showed that it twice inhibits the induction of phenoloxidase activity, through which the melanization manifests. As a result, we approached further to the identification of serpin PC’s native targets and function.