PubMed · 4116940
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1972-11-11. Apoptosis.. https://pubmed.ncbi.nlm.nih.gov/4116940/
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Glucose-mediated repression of autolysis and sporulation was studied in submerged Emericellanidulans (anam. Aspergillus nidulans) cultures. Null mutation of the creA gene, which encodes the major carbon catabolite repressor CreA in E. nidulans, resulted in a hyperautolytic phenotype characterized by increased extracellular hydrolase production and dry cell mass declination. Interestingly, glucose, as well as the glucose antimetabolite 2-deoxy-d-glucose, repressed autolysis and sporulation in both the control and the creA null mutant strains suggesting that these processes were also subjected to CreA-independent carbon regulation. For example, the glucose-mediated, but CreA-independent, repression of the sporulation transcription factor BrlA was likely to contribute to the negative regulation of conidiogenesis by glucose. Although CreA played a prominent role in the regulation of autolysis via the repression of genes encoding important autolytic hydrolases like ChiB chitinase and PrtA protease the age-related production of the chitinase activity was also negatively affected by the down-regulation of brlA expression. However, neither CreA-dependent nor CreA-independent elements of carbon regulation affected the initiation and regulation of cell death in E. nidulans under carbon starvation.
Calpain 3, commonly called p94 in the literature, is the abundant skeletal muscle-specific calpain that is genetically linked to limb girdle muscular dystrophy type 2A. Recently, we showed that p94's insertion sequence 1 (IS1) is a propeptide that must be autoproteolytically cleaved to provide access of substrates and inhibitors to the enzyme's active site. Removal of IS1 from the core of p94 by recombinant methods produced a fully active enzyme. Here we have resolved the discrepancies in the literature about the Ca(2+) requirement of p94 using the protease core. Even at substoichiometric levels of Ca(2+), and in competition with EDTA, autoproteolyzed enzyme slowly accumulated. Because the initial autoproteolytic cleavage is an intramolecular reaction, transient binding of two Ca(2+) ions to the core would be sufficient to promote the reaction that is facilitated by having the scissile peptide lying close to the active site cysteine. The second autolytic cleavage was much slower and required higher Ca(2+) levels, consistent with it being an intermolecular reaction. Other metal ions such as Na(+), K(+), and Mg(2+) cannot substitute for Ca(2+) in catalyzing the intramolecular autoproteolysis of the p94 core or in the subsequent hydrolysis of exogenous substrates. These metal ions increase moderately the activity of this enzyme but only at very high concentrations. Thus, the proteolytic activity of the core of p94 and its deletion mutant lacking NS and IS1 was shown to be strictly Ca(2+)-dependent. We propose a two-stage model of activation of the proteolytic core of p94.
The ubiquitous protein LuxS with S-ribosylhomocysteinase activity is involved in S-adenosyl methionine detoxification, C-1 unit recycling and the production of autoinducers that allow the cell to sense and respond to cell density. Independent reports describe the impact of LuxS deficiency on Streptococcus pneumoniae virulence in the mouse. In vitro, LuxS deficiency confers discrete phenotypes. A combined approach using genetic dissection and mixed-culture experiments allowed the involvement of LuxS in the developmental physiology of S. pneumoniae to be investigated. Functional LuxS was found to be related on the one hand to down-regulation of competence, and on the other hand to attenuation of autolysis in cultures entering stationary phase. The competence phenotype of luxS mutant bacteria was complemented by media conditioned by competence-defective ComAB0 bacteria, but not by BSA. The autolytic phenotype was complemented by BSA, but not by conditioned supernatants. It is suggested that the impact of LuxS on competence, but not on autolysis, involves cell-cell communication. The phenotype of luxS mutant strains reveals a hierarchy in the competence regulatory networks of S. pneumoniae.