Functional analysis of pancreatic secretory trypsin inhibitor protein with amino acid substitution

Abstract

Introduction: The pancreatic secretory trypsin inhibitor (PSTI) is thought to be a specific inactivation factor of intrapancreatic trypsin activity. N34S mutation of PSTI was reported in chronic pancreatitis patients from all over the world including us, and is thought to be one of the predisposing factors for pancreatitis. The N34S mutation located close to the reactive lysine–isoleucine site (K41∼I42) might lead to a decreased inhibitory capacity. N34S is also in complete linkage with other intronic sequence variants such as IVS1-37T→C and IVS3-65insTTTT. Materials/Methods: Based on the hypothesis above, we performed biochemical experiments. (I) Activity of recombinant PSTI protein with N34S was compared to that of the wild type. (II) Molecular weight of PSTI from a patient with N34S was analysed by Western blotting to check the possibility of abnormal splicing (e.g. splice-out of exon 4). Results: (I) The function of N34S PSTI remained unchanged compared to wild-type PSTI. (II) The molecular weight of PSTI protein from a patient with N34S was not altered. Conclusion: We could not detect any functional or configurational abnormalities of N34S PSTI protein by the two experiments mentioned above. Other factors, such as translational abnormality by intronic mutation, may be associated with the predisposition to pancreatitis.