Amino acid sequence of serine protease inhibitor CI-1 from barley. Homology with barley inhibitor CI-2, potato inhibitor I, and leech eglin

Abstract

Three molecular forms of a protein inhibitor of chymotrypsin and microbial alkaline proteases have been isolated from Hiproly high-lysine barley. Automated Edman degradation of one of these inhibitor preparations (CI-1C) resulted in the following amino acid sequence (77 residues in total): Tyr-Pro-Glu-Pro-Thr-Glu-Gly-Ser-Ile-Gly-Ala-Ser-Gly-Ala-Lys-Thr-Ser-Trp-Pro-Glu-Val-Val-Gly-Met-Ser-Ala-Glu-Lys-Ala-Lys-Glu-Ile-Ile-Leu-Arg-Asp-Lys-Pro-Asn-Ala-Gln-Ile-Glu-Val-Ile-Pro-Val-Asp-Ala-Met-Val-Pro-Leu-Asn-Phe-Asn-Pro-Asn-Arg-Val-Phe-Val-Leu-Val (His, Lys, Ala, Thr, Thr, Val, Ala, Glx, Val, Ser, Arg) Val-Gly. The inhibitor (CI-1) is homologous with another barley inhibitor (CI-2), with potato inhibitor I and with the elastase-cathepsin G inhibitor eglin from the leech Hirudo medicinalis (30–50% of the amino acid residues in identical positions). This established «family of cystine-independent inhibitors» also showed some sequence similarities with the cystine-free yeast proteinase B inhibitors 1 and 2. In the reactive site region homologies with the cystine-rich inhibitors of the «Kazal pancreas secretory inhibitor» and the «Streptomyces subtilisin inhibitor» families were observed.