Characterization and expression of the pepsinogen C gene and determination of pepsin-like enzyme activity from orange-spotted grouper ( Epinephelus coioides)

Abstract

One pepsinogen C gene was cloned from the gastric mucosa of orange-spotted grouper ( Epinephelus coioides) for the first time. This gene consisted of nine exons interrupted by eight introns. The nucleotide sequence with the coding region and 3′-flanking region was also determined. The deduced polypeptide sequence was composed of a prosegment of 55 residues and a pepsin moiety of 332 residues. The putative substrate-binding subsites were well conserved among fish with the exception of the residue Thr292 in the S 2 subsite and displayed a significantly low value of hydropathy and high flexibility. These differences may affect the catalytic function and substrate specificity. RT-PCR assay followed by Southern blot revealed that pepsinogen C was primarily distributed in the stomach, but also expressed in various tissues, including gill, intestine, pyloric ceca, esophagus and ovary. This is the first observation of pepsinogen C expression in various tissues of one species of fish. Pepsinogen C transcript was first detected at 41 dph and continuously expressed through to adult fish, coinciding with the pepsin-like enzymes activity during developmental stages. Pepsin-like enzymes activity was present in the early larva stage, increased significantly at the end of juvenile stage and remained at similar levels in young fish and adult. Northern blot analysis suggested that three forms of transcripts were expressed differently during experimental periods. Our results suggest that pepsin C possesses any other functions besides digestion.