Evidence for controlled autoproteolysis of alkaline protease. A mechanism for physiological regulation of conidial discharge in Conidiobolus coronatus.

The alkaline serine protease of Conidiobolus coronatus was shown to be involved in its conidial discharge [Phadatare, S., Srinivasan, M. C., Deshpande, M. (1989) Arch. Microbiol. 153, 47-49]. To understand the regulation of conidial discharge, the mechanism of control of protease activity was investigated, which revealed the presence of two electrophoretically separable intracellular proteases (protease I and protease II). The formation of smaller and less-active protease II coincided with the decrease in conidial discharge. In order to trace the origin of protease II, the corresponding purified extracellular enzymes were compared with respect to their biochemical, physiochemical and immunological properties. The biochemical properties, such as optimum pH and temperature, stability, sensitivity to metal ions and substrate specificity were closely similar for both proteases. Amino acid analysis revealed that protease II is completely similar to protease I, though protease I contains an additional portion which is not contained in protease II. Western-blot ELISA, immunotitration and determination of antigenic valencies also revealed the structural similarity between the two proteases. Purified protease I showed partial degradation to protease II in vitro, the process being sensitive to phenylmethylsulfonyl fluoride, indicating its proteolytic nature. These results suggest that the formation of a less-active protease by autoproteolysis represents a novel means of physiological regulation of protease activity, which in turn regulates the conidial discharge in C. coronatus.