Trypsin and chymotrypsin inhibitor peptides from the venom of Chinese Daboia russellii siamensis

Abstract

Two trypsin inhibitors and one chymotrypsin inhibitor from Chinese Daboia russellii siamensis venom, denoted as CBPTI-1, CBPTI-2 and CBPTI-3 were purified, characterized and cloned from lyophilized venom-derived cDNA libraries. The N-terminus of CBPTI-1 was modified and not amenable to Edman degradation sequencing, however an internal partial sequence was found to be SGRCRGHLRRIYYNPDSNKCE. The N-termini of CBPTI-2 and CBPTI-3 were unmodified and their partial sequences were established as HDRPTFCNLAPESGRCRAH and HDRPKFCYLPADPGECMAYIRSFYYDS respectively. From cloning studies CBPTI-1 was found to consist of 66 amino acid residues, while CBPTI-2 and CBPTI-3 precursors consist of 60 amino acid residues, including 6 cysteine residues. Another cDNA sequence (CBPTI-4) was also obtained. Alignment of cDNA sequences showed that CBPTI-3 exhibited similar sequence homology to CBPTI-4 cDNA except for an 8 nucleotide deletion in the open-reading frame. CBPTI-1 and CBPTI-2 were demonstrated to be potent trypsin inhibitors, but were also shown to be effectively potent in chymotrypsin inhibition. The Ki values of CBPTI-1 and CBPTI-2 for trypsin inhibition were 4.07 × 10−7 M and 6.66 × 10−7 M, respectively, and they were non-competitive in their activity. CBPTI-3 showed chymotrypsin inhibition activity with a Ki value of 2.55 × 10−9 M, but did not show trypsin inhibitor activity.