Extracellular acid proteases from Neurospora crassa

Area of Science:

• Enzymology
• Microbial Physiology
• Molecular Biology

Background:

• Neurospora crassa produces alkaline, neutral, and acid proteases.
• Alkaline and neutral proteases are induced by exogenous protein and secreted upon limitation of carbon, nitrogen, or sulfur.
• Acid proteases also require protein induction but exhibit differential regulation based on specific nutrient deprivation.

Purpose of the Study:

• To investigate the differential regulation of acid proteases in Neurospora crassa.
• To characterize two specific acid proteases, AcP and M-2, in response to nutrient limitation.

Main Methods:

• Culture filtrates of Neurospora crassa were analyzed for protease activity.
• Enzyme induction and secretion were studied under varying nutrient limitations (carbon, nitrogen, sulfur).
• Partial purification of AcP and M-2 was achieved using ultrafiltration, cation-exchange chromatography, and gel filtration.

Main Results:

• Three distinct acid proteases were identified: AcP, M-1, and M-2.
• AcP secretion was high under sulfur limitation, low under nitrogen limitation, and undetectable under carbon limitation.
• M-1 and M-2 showed specific secretion patterns related to nitrogen, carbon, and sulfur limitation.
• AcP (66 kDa) is pepstatin-inhibitable, stable pH 3.0-6.0, optimal pH 4.0.
• M-2 (18 kDa) is chelator-sensitive, stable pH 1.6-5.5, optimal pH 4.5.

Conclusions:

• Acid protease secretion in Neurospora crassa is differentially regulated by specific nutrient limitations, unlike alkaline and neutral proteases.
• The regulation of acid proteases may not occur at the transcriptional level.
• Characterization of AcP and M-2 provides insights into their distinct biochemical properties and roles.