Characterization and Identification of Partial Amino Acid Sequence of a Novel Elastase Inhibitor, Asnidin from Aspergillus nidulans

[Studies on Elastase and Elastase Inhibitor from Aspergillus flavus]

The biological properties of elastase and Aspergillus flavus elastase inhibitor (AFLEI) from A. flavus were examined. Pathogenicity of elastase was investigated in mice immunocompromised with cyclophosphamide, cyclosporine, prednisolone and carrageenan. Compared to cyclophosphamide immunocompromised mice treated with the spores of elastase nonproducing strain, cyclophosphamide immunocompromised mice treated with the spores of elastase producing strain had a significantly shorter survival rate. Molecular mass of AFLEI was determined to be 7525.8 Da. The elastolytic activity of elastases from A. flavus, and human leukocytes were inhibited by AFLEI. The primary structure of AFLEI was determined by the Edman sequencing procedure. The search for amino acid homology with other proteins demonstrated that amino acid residues 1 to 68 of AFLEI are 100% identical to residues 20 to 87 of the hypothetical protein AFUA_3G14940 of A. fumigatus. When immunocompromised mice administered of cyclophosphamide were infected by inhalation of A. flavus then administered amphotericin B (AMPH) alone or in combination with AFLEI, survival rate tended to be higher with combination treatment than with AMPH alone. Moreover, although extensive bleeding was seen in pathology sections taken from rat lung resected 24 h after elastase was administered to the lung via the bronchus, this bleeding was inhibited by AFLEI. The X-ray analysis has revealed that the structure of this inhibitor was wedge shaped and composed of a binding loop and a scaffold protein core. As synthetic-inhibitor strongly inhibited cytotoxicity induced by elastase in human-derived cells, it could prove beneficial for the treatment of pulmonary aspergillosis.

Microbial serine protease inhibitors and their therapeutic applications

Serine protease inhibitors, inhibit serine proteases either partially or completely after forming complexes with their respective proteases. Protease actions are significant for many physiological pathways found in living forms and any anomalies may lead to numerous physiological complications. Each cell or organism has its own mechanism for controlling these protease actions. It is often regulated by the action of inhibitors or activators. Among the proteases, serine proteases are the most common that are involved in many life and death processes. Selective inhibitors of physiologically relevant proteases can be used as a lead compound for the drug development. Therefore, it is imperative to identify small peptides and proteins that selectively inhibit serine proteases from various sources. Microbes can be considered as a major source of diverse serine protease inhibitors since they have the prominent and diverse domain in nature. Most of the microbial serine protease inhibitors are intracellular and few are extracellular. Microbes produce protease inhibitors for protection against its own proteases or against other environmental factors. The status and future prospects of microbial serine protease inhibitors and their therapeutic benefits in treating cancer, blood coagulation disorders and viral infections, are reviewed here.