Chronic pancreatitis associated with an activation peptide mutation that facilitates trypsin activation

Background & Aims: Mutations of the cationic trypsinogen have been describe d in hereditary pancreatitis. We report a new trypsinogen mutation in the a ctivation peptide of the proenzyme in a family with chronic pancreatitis. M ethods: The coding region of the cationic trypsinogen gene was sequenced af ter polymerase chain reaction amplification. The following peptides homolog ous to the N-terminal end of cationic trypsinogen were synthesized tone-let ter code, mutated amino acid underlined): wild-type peptide, APFDDDDKIVGG; pD22G, APFDDDGKIVGG; pK23R, APFDDDDRIVGG. The sequences of pD22G and pK23R correspond to the recently identified mutation K23R and to the mutation des cribed here (D22G). To mimic trypsinogen activation, these peptides were di gested with trypsin for 30 minutes at pH 5.0-8.0, and the fragments were an alyzed by high-performance liquid chromatography. Results: In a family with clinical evidence of hereditary chronic pancreatitis, a missense mutation of codon 22 (GAC-->GGC) of the cationic trypsinogen was found. This mutatio n results in a substitution of aspartic acid by glycine; therefore, the mut ation was called D22G. Chromatographic analysis of tryptic digests of the p eptides pD22G and pK23R showed hydrolysis rates of 22% and 75%, respectivel y, whereas the wild-type peptide was hydrolyzed at only 6%. The cleavage ra tes were reduced at lower pH, and no hydrolysis occurred without trypsin. C onclusions: The activation peptides of the trypsinogen variants D22G and K2 3R could be released at a higher rate than in wild-type trypsinogen, result ing in increased amounts of trypsin in the pancreas, which could initiate p ancreatitis.