Abstract
In the present study we show that hemocytes in the freshwater crayfish Pacifastacus leniusculus express two different transglutaminases. We describe the sequence of a previously unknown TGase (Pl_TGase1) and named this as Pl_TGase2 and compared this sequence with similar sequences from other crustaceans. The catalytic core domain is similar to the previously described TGase in P. leniusculus, but Pl_TGase2 has significant differences in the N-terminal and C-terminal domains. Further, we show conclusive evidences that these different transglutaminases are specific for different hemocyte types so that Pl_TGase1 is expressed in the hematopoietic tissue and in the cytoplasm of semigranular hemocytes, while Pl_TGase2 is expressed in vesicles in the granular hemocytes. By in situ hybridization we show that both Pl_TGase1 and Pl_TGase2 mRNA are present only in a subset of the respective hemocyte population. This observation indicates that there may be different subtypes of semigranular as well as granular hemocytes which may have different specific functions.
Highlights
Coagulation is an important defense and wound healing reaction in crustaceans as well as in other animals, and since the first discovery of a crosslinking transglutaminase in lobster plasma by Lorand et al, 1966 [1], this enzyme has been proven to be important in the clotting reaction in crustaceans among which the freshwater crayfish Pacifastcus leniusculus is most studied [2]
Semigranular cells, from the hematopoietic tissue (HPT) into the circulation is induced by the cytokine astakine1 (Pl_Ast1) [20,23], and recently, we showed that this Pl_Ast1 acts by blocking transglutaminase activity directly as a noncompetitive inhibitor [20,24]
We previously showed that Pl_TGase1 is an abundant protein in both the HPT and hemocytes, and the expression is especially high in semigranular cells (SGC), which is similar to the enzyme activity of TGase [20]
Summary
Coagulation is an important defense and wound healing reaction in crustaceans as well as in other animals, and since the first discovery of a crosslinking transglutaminase in lobster plasma by Lorand et al, 1966 [1], this enzyme has been proven to be important in the clotting reaction in crustaceans among which the freshwater crayfish Pacifastcus leniusculus is most studied [2]. Apart from the crosslinking, by its transamidation activity, transglutaminases in mammals have been shown to have GTP-binding activity, and upon GTP-binding the enzyme changes into a catalytically inactive conformation [14]. Such activity still has to be shown for crustacean transglutaminases
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