Characterization and primary structure of elastase inhibitor, AFLEI, from Aspergillus flavus

The amino acid sequence of elastase inhibitor, AFLEI, isolated from Aspergillus flavus was determined by the Edman sequencing procedure of peptides derived from digests utilizing clostripain. A molecular weight of 7,525.8 was observed by TOF-MS. AFLEI contained 68 amino acid residues and has a calculated molecular weight of 7,526.2. The search for amino acid homology with other proteins demonstrated that amino acid residues 1 to 51 of AFLEI are 100% identical to residues 20 to 70 of the hypothetical protein Afu3g14940. The Michaelis constant (Km) for succinyl L-alanyl- L-alanyl- L-alanyl p-nitroanilide (STANA), and inhibition constant (Ki), for elastase of AFLEI, were found to be 6.7 x 10(2) microM and 4.0 x 10(-2) microM, respectively. Inhibitory activity was compared with six protease inhibitors (ulinastatin, nafamostat mesilate, sivelestat sodium hydrate, gabexate mesilate, elastatinal and elafin). The other six protease inhibitors demonstrated very weak inhibitory activity by comparison with AFLEI.