A transglutaminase involved in the coagulation system of the freshwater crayfish, Pacifastacus leniusculus. Tissue localisation and cDNA cloning

The crayfish haemolymph can form stable and insoluble clots by a transglutaminase (TGase)-catalysed crosslinking reaction between the soluble clotting protein molecules from the plasma. The crayfish haemocytes, both semigranular and granular cells, as well as the muscle tissue, contain TGase activity, whereas the hepatopancreas and plasma have no TGase activity. A 3199 bp cDNA encoding a TGase was isolated from a crayfish haemocyte cDNA library. The deduced protein comprises 766 amino acid residues and has a calculated molecular mass of between 85 930 and 86 034 kDa due to four amino acid variations. This gene is expressed as a single 4·9 kb transcript exclusively in the haemocytes and at very low levels in muscle and the hepatopancreas. Sequence comparison shows that this TGase has significant similarities to other TGases from invertebrates and mammals.