Identification and cloning of the second type transglutaminase from Litopenaeus vannamei, and its transcription following pathogen infection and in relation to the haemolymph coagulation

Complementary (c)DNA encoding transglutaminaseII (TGII) messenger (m)RNA of white shrimp, Litopenaeus vannamei, was cloned from haemocytes by a reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) using oligonucleotide primers based on the TG sequence of the horseshoe crab, Tachypleus tridentatus (accession no.: BAA02134), tiger shrimp, Penaeus monodon (AAV49005; AAO33455), kuruma shrimp, Marsupenaeus japonicus (BAD36808) and Pacifastacus leniusculus (AAK69205) TG. The 2405-bp cDNA contained an open reading frame (ORF) of 2292 bp, a 31-bp 5′-untranslated region (UTR), and an 82-bp 3′-UTR containing a poly A tail. The molecular mass of the deduced amino acid (aa) sequence (764 aa) was 85.9 kDa with an estimated pI of 5.32. The L. vannamei TGII (abbreviated LvTGII) contains a typical TG-like homologue, two putative integrin binding motif (RGD and KGD), and five calcium-binding sites; three catalytic triad is present as in arthropod TG. Sequence comparison and phylogenetic analysis revealed that shrimp TG can be separated into two groups, STGI and STGII, and LvTGII is more closely related to STGII than to STGI. LvTGII mRNA was detected in all tested tissues of L. vannamei, and was highly expressed in haemocytes. The haemocytes of L. vannamei injected with Vibrio alginolyticus showed a significant increase of LvTGI and LvTGII mRNA expression at 6 h followed by a notable decrease at 24 h in LvTGI and a continually increase in LvTGII indicating a complementary effect, which implied that both LvTGs involved in the immune response of shrimp, and LvTGII was more important in the later defense response. The gene silencing of LvTGII in shrimp significantly decreased LvTGII expression and TG activity of haemocytes, and significantly increased clotting time of haemolymph, suggests that the cloned LvTGII is a clotting enzyme involved in haemolymph coagulation of L. vannamei. In conclusion, the cloned LvTGII is a clotting enzyme involved in coagulation of haemolymp and immune response of white shrimp, L. vannamei.