Sequence analysis and tissue expression pattern of Sparus aurata chymotrypsinogens and trypsinogen

Two apparently full-length cDNA clones encoding chymotrypsinogens I and II (CHTRI, 1022 bp; CHTRII, 909 bp) and one cDNA clone encoding trypsinogen II (TRPII, 848 bp) were isolated from a cDNA library prepared from gilthead sea bream (Sparus aurata) liver. The deduced amino acid sequences of the isolated cDNAs contain highly conserved residues essential for serine protease catalytic activity and conformational maintenance. The deduced amino acid sequences of CHTRI and CHTRII are 261 aa and 277 aa long, respectively, and share only 61% identity. Sea bream CHTRII appears to be the longest of all known teleostean chymotrypsinogen forms and contains a high number of methionine residues. Compared with CHTRI, CHTRII is more hydrophobic and has a lower isoelectric point. On the other hand, deduced amino acid sequence of TRPII is 241 aa long and has a signal peptide of thirteen amino acid residues and an activation peptide of seven amino acids long. In contrast to CHTRI and CHTRII, TRPII has a low isoelectric point (4.95), which makes it anionic at neutral pH. Northern blot analysis revealed that liver is the major transcription site for all zymogens. As expected, all zymogen transcripts were detected in parts of the digestive tract (stomach, pyloric caeca, anterior and posterior intestine) and pyloric caeca presented the most intense expression. In all tissues and amongst all zymogens, TRPII constitutive expression was the highest.