cDNA cloning, identification, tissue localisation, and transcription profile of a transglutaminase from white shrimp, Litopenaeus vannamei, after infection by Vibrio alginolyticus

Complementary (c)DNA encoding transglutaminase (TG) 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 (AAL78166); and Pacifastacus leniusculus (AF336805). The 2638-bp cDNA contained an open reading frame (ORF) of 2172 bp, a 55-bp 5′-untranslated region (UTR), and a 411-bp 3′-UTR containing a poly A tail. The molecular mass of the deduced amino acid (aa) sequence (757 aa) was 84.9 kDa with an estimated pI of 5.2. The L. vannamei TG (abbreviated LvTG) contains a typical transglutaminase-like homologue, a putative integrin-binding motif (RGD), and four calcium-binding sites; a catalytic triad is present as in arthropod TG. Sequence comparison and phylogenetic analysis revealed that shrimp TG can be separated into two subgroups, STGS1 and STGS2, and LvTG is more closely related to STGS1 than to STGS2. LvTG mRNA and TG activities were detected in all tested tissues of L. vannamei, with LvTG mainly being synthesised in haemocytes. However, the pattern of LvTG mRNA expression was not directly correlated with TG activity. The haemocytes of L. vannamei injected with Vibrio alginolyticus showed a significant decrease of TG activity at 3 h and a significant increase of LvTG mRNA expression at 6 h followed by a notable decrease from 12 to 24 h, which indicated that cloned LvTG was involved in the immune response of shrimp. The results also imply that more than one type of TG may be involved in the defense response in L. vannamei.