Amino Acid Sequences of Kunitz-type Protease Inhibitors from the Sea Anemone Actinia equina

Abstract

Four serine protease inhibitors (AEPI-I, II, III and IV) were isolated from the sea anemone Actinia equina by a slight modification of our previous method. When the native inhibitors were applied to a sequencer, 36, 36, 35, and 37 amino acid residues from the N-terminus were identified for AEPI-I, II, III, and IV, respectively. The remaining sequences of AEPI-I and II were deduced from analyses of peptide fragments obtained by digestion of S-carboxamidomethylated molecules with either V8 protease or lysyl endopeptidase. Both inhibitors were composed of 59 amino acid residues including 6 half-Cys residues and their sequences were very similar to each other with replacements at only two positions. The positions of half-Cys residues and the entire-chain homology identified these inhibitors as members of the Kunitz-type family. Notably, the sequences of the two contact sites with serine proteases were highly conserved within the sea anemone inhibitors.