Amino acid sequence of a trypsin inhibitor from a Spirometra (Spirometra erinaceieuropaei)

A trypsin inhibitor that is highly homologous with bovine pancreatic trypsi n inhibitor (BPTI) was co-purified along with RNase from Spirometra (Spirom etra erinaceieuropaei). The amino acid sequence of this inhibitor (SETI) an d the nucleotide sequence of the cDNA encoding this protein Acre determined by protein chemistry and gene technology. SETI contains 68 amino acid resi dues and has a molecular mass of 7798 Da. SETI has 31 amino acid residues t hat are identical with BPTI's sequence, including 6 half-cystine and 5 arom atic amino acid residues. The active site Lys residue in BPTI is replaced b y an Arg residue in SETI. SETI is an effective inhibitor of trypsin and mod erately inhibits alpha -chymotrypsin, but less inhibits elastase or subtili sin. SETI was expressed by, E. coli containing a PelB vector carrying the S ETI encoding cDNA, an expression yield of 0.68 mg/l was obtained. The phylo genetic relationship of SETI and the other BPTI-like trypsin inhibitors was analyzed using most likelihood inference methods.