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Extracellular proteases of Aspergillus flavus. Fungal keratitis, proteases, and pathogenesis
1Department of Biophysics, University of Rochester, School of Medicine, New York.
Abstract:
To get a better understanding of the possible role of proteases in the pathogenesis of fungal keratitis, the extracellular proteases of a clinical isolate of Aspergillus flavus, from a severe case of keratitis, were identified and partially characterized. This strain, designated CU226/88, was grown with a variety of substrates as nitrogen sources, under conditions that would be expected to derepress the production of extracellular proteases. When grown on minimal medium with milk protein as a nitrogen source, the fungus appeared to produce primarily a metalloprotease, which has a zinc cofactor. When grown with insoluble collagen or elastin as a nitrogen source, a serine protease and cysteine protease, as well as the metalloprotease, are produced. Strain CU226/88 can grow with collagen, but not elastin, as the sole source of carbon as well as nitrogen. It is possible that the collagenase activity is a mediator of the severe corneal destruction caused by this isolate.
Insights
This study identified extracellular proteases from Aspergillus flavus, a fungus causing severe keratitis. Collagenase activity may contribute to corneal tissue destruction in fungal keratitis.
Area of Science:
- Microbiology
- Ophthalmology
- Biochemistry
Background:
- Fungal keratitis is a severe eye infection.
- Proteases play a role in pathogen virulence.
- Aspergillus flavus is a common cause of fungal keratitis.
Observation:
- Extracellular proteases from a clinical Aspergillus flavus isolate (CU226/88) were studied.
- The fungus was cultured on various nitrogen sources to induce protease production.
- Protease production varied with different substrates.
Findings:
- A metalloprotease (zinc-dependent) was primarily produced on milk protein.
- Serine and cysteine proteases, along with metalloprotease, were produced on collagen or elastin.
- Aspergillus flavus CU226/88 utilized collagen but not elastin as a sole carbon and nitrogen source.
Implications:
- The identified proteases, particularly collagenase, may mediate corneal damage in fungal keratitis.
- Understanding these virulence factors can inform treatment strategies for fungal keratitis.
- Further characterization of Aspergillus flavus proteases is warranted.