More than one type of transglutaminase in invertebrates? A second type of transglutaminase is involved in shrimp coagulation.

Coagulation (clot formation) forms a physical barrier to prevent the loss of body fluid and dissemination of microbes into the haemocoel after injury or infection. Its quickness and efficiency are essential for the survival of invertebrates that rely solely on innate immunity. Transglutaminase (TG) catalyses intermolecular or intramolecular epsilon-(gamma-glutamyl) lysine bond formation, resulting in a protein polymerisation, and plays a role in blood coagulation and post-translational protein remodelling. In the present study, we cloned a TG from shrimp (Penaeus monodon) haemocyte cDNA. It was assigned as shrimp transglutaminase II (STG II). The STG II cDNA consists of a coding region of 2,274bp. The deduced protein has 757 amino acid residues with a calculated molecular mass of 85,000 Da and an isoelectric point of 5.48. RT-PCR results showed a significant level of STG II expression in haemocytes but not in hepatopancreas, in contrast to shrimp STG I (AY074924.1). The genetic distance between STG II and STG I is much larger than the distance between STG II and the TG of the kuruma shrimp (Marsupenaeus japonicus). Evidence based on tissue distribution and genetic distance suggests that no less than two types of shrimp TG exist that are encoded at different chromosomal locations. The recombinant STG II (rSTG II) incorporated a TG-specific substrate, dansylcadaverine (DCA), into clottable proteins (CP) in a calcium dependent manner. Other haemocyte- or plasma-derived TG substrate is not required for CP polymerisation but may be necessary for stable clot formation. The rSTG II catalysed clottable proteins into a long chain under transmission electron microscopy (TEM) observation. In conclusion, STG II is characterized as a haemocyte TG and is involved in coagulation.