LTCI, a novel chymotrypsin inhibitor of the potato I family from the earthworm Lumbricus terrestris. Purification, cDNA cloning, and expression.

A novel chymotrypsin inhibitor of the potato I protease inhibitor family from the earthworm Lumbricus terrestris was purified. The inhibitor, named LTCI, was isolated by methanol extraction, affinity chromatography on immobilized methylchymotrypsin, and ion exchange chromatography followed by RP-HPLC. The 7076 Da inhibitor consists of a single polypeptide chain of 64-amino-acid residues without disulfide bridges. LTCI is the first of the potato I protease inhibitors with Tyr in position P1 of the reactive site. cDNA analysis revealed that LTCI is produced as a 86-amino-acid precursor with a 22-amino-acid secretory signal peptide. RT-PCR analysis demonstrates that LTCI mRNA is expressed in body wall, intestine, and coelomocytes. The recombinant LTCI was produced in Escherichia coli as a fusion protein with intein and chitin binding domain using IMPACT-CN system.