CLONING AND SEQUENCE-ANALYSIS OF A CDNA-ENCODING SALMON (ONCHORHYNCHUS-KETA) LIVER TRANSGLUTAMINASE

We isolated cDNA clones encoding a transglutaminase (TGase: EC 2.3.2.1 3) from a salmon (Onchorhynchus keta) cDNA library prepared from the l iver. In the cDNA sequence combined, an open reading frame coding for a protein of 680 aa was found. The deduced sequence showed a considera ble similarity (62.4%) to that of red sea bream TGase. By comparison o f sequence similarity to other TGases, the structure of salmon TGase w as like tissue type TGases, rather than membrane-associated type or pl asma type TGases. As a structural feature of salmon TGase, 3 aa residu es were substituted in the 25 aa sequence around the active site Cys r esidue, which is conserved among several tissue type TGases. The criti cal residues thought to form the catalytic-center triad (Cys(272), His (331), and Asp(301)) were found in the highly conserved region, but th e region surrounding Tyr(511), which corresponds to the residue partic ipates in hydrogen-bond interactions of active center domain, was less similar to other TGases, except for red sea bream TGase. These findin gs suggests that the overall structure of fish TGase resembles tissue- type TGases, but has some unique structure.