Specificity of five intracellular proteinases of Neurospora crassa

Protein mapping and genome expression variations in the basidiomycete Agrocybe aegerita

A procedure suitable for the extraction and mapping of total proteins from the basidiomycete, Agrocybe aegerita, was developed. A. aegerita mycelia were fragmented either with a Dangoumeau grinder, an X-press bomb or a sonicator and the efficiency of these three disruption methods were compared. The extraction buffer composition was optimized to avoid proteolytic activities. 2D-SDS-PAGE analysis of protein extracts showed that the rate of reproducibility depending on extractions and electrophoretic separations was always greater than 96% for all strains. The differences in efficiency observed between the breaking procedures indicate that the A. aegerita cell wall is more mechanically resistant than that of other basidiomycetes. The efficient action of protease inhibitors (PMSF and SDS) showed that A. aegerita mycelia contains numerous and/or highly active proteases. Reproducibility of protein extraction and separation methods allowed the establishment and the comparison of standard maps. Qualitative and quantitative variations in gene products between a wild dikaryotic strain and 11 homokaryotic strains from its progeny were examined. The genetic diversity, determined by comparing the distribution of proteic variations in 11 homokaryons from the same progeny, was comparable to that observed between co-isogenic homokaryons of another basidiomycete.

Structural features of normal and complemented forms of the Neurospora isopropylmalate isomerase

The isopropylmalate isomerase (EC 4.2.1.33) of Neurospora crassa is a globular protein consisting of a single polypeptide chain with a molecular weight of about 90,000. The isomerase cannot easily be freed of a contaminating protease which cleaves the enzyme into two major fragments, one of approximately 56,000 and the other 37,000 daltons. This suggests that the folded polypeptide chain may contain some hinge point or loop exposed on the surface which makes it susceptible to proteolytic attack. Most of the isomerase activity extracted from the wild-type strain is in monomer form. However, a small fraction of the activity in crude extracts is found in multimeric aggregates, and the active isomerase extracted from complementing leu-2 heterokaryons consists entirely of dimers and higher multimers. These observations suggest that, though active as a monomer, a significant fraction of the normal enzyme might be organized in multimeric form within the cell.