Molecular cloning and characterization of two isoforms of trypsinogen from anchovy pyloric ceca

Complementary DNA clones encoding two isoforms of trypsinogen were isolated from the pyloric ceca of anchovy by rapid amplification of cDNA ends (RACE). Nucleotide sequences of isolated clones encoded, in addition to characteristic signal and activation peptides, two isoforms of trypsin containing 220 and 221 amino acid residues. Both enzymes contained the catalytic triad of a serine protease, together with the residues determining substrate specificity. The anchovy trypsins showed a high amino acid identity of about 80% to those of other fish species. Southern blot analysis with a probe cross-reactive to both isoforms showed a complex genomic pattern. Northern blot analysis with the same probe revealed the highest expression of messenger RNA in the pyloric ceca. Structural parameters possibly involved in higher catalytic properties of fish trypsin were examined by three-dimensional modeling, which included deletion in the autolysis loop, lack of Tyr-151 at the entrance of the S1 pocket, and distribution of charged residues.