[The role of virulence factor of elastolytic proteinase from Aspergillus fumigatus]

Biological properties of elastase inhibitor, AFLEI from Aspergillus flavus

The biological properties of elastase inhibitor from Aspergillus flavus (AFLEI) were investigated. AFLEI was produced at the highest rate when casamino acid was used as the nitrogen source. When a mixture of AFLEI (approx. molecular weight, 7,500) and elastase from A. flavus (approx. molecular weight, 40,000) was detected using anti-AFLEI antibody, molecular weight of the detected mixture was approximately 48,000, indicating that AFLEI and elastase bound at a proportion of 1 : 1. When immunocompromised mice administrered of immunosuppressive (cyclophosphamide) were infected by inhalation of A. flavus and administered amphotericin B (AMB) alone or in combination with AFLEI, survival rate tended to be higher with combination treatment than with AMB alone. Moreover, although extensive bleeding was seen in pathology sections taken from rat lung resected 24 hr after purified elastase was administered to the lung via the bronchus, this bleeding was inhibited by AFLEI. These findings indicate that for the treatment of aspergillosis, combination of an existing antifungal agent with AFLEI can be expected to provide greater therapeutic benefits than administration of an antifungal agent alone.

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.