Evidence of morphology-specific isozymes inCandida albicans

Farnesol-induced apoptosis in Candida albicans

Farnesol, a precursor in the isoprenoid/sterol pathway, was recently identified as a quorum-sensing molecule produced by the fungal pathogen Candida albicans. Farnesol is involved in the inhibition of germination and biofilm formation by C. albicans and can be cytotoxic at certain concentrations. In addition, we have shown that farnesol can trigger apoptosis in mammalian cells via the classical apoptotic pathways. In order to elucidate the mechanism behind farnesol cytotoxicity in C. albicans, the response to farnesol was investigated, using proteomic analysis. Global protein expression profiles demonstrated significant changes in protein expression resulting from farnesol exposure. Among the downregulated proteins were those involved in metabolism, glycolysis, protein synthesis, and mitochondrial electron transport and the respiratory chain, whereas proteins involved in folding, protection against environmental and oxidative stress, actin cytoskeleton reorganization, and apoptosis were upregulated. Cellular changes that accompany apoptosis (regulated cell death) were further analyzed using fluorescent microscopy and gene expression analysis. The results indicated reactive oxygen species accumulation, mitochondrial degradation, and positive terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) in the farnesol-exposed cells concurrent with increased expression of antioxidant-encoding and drug response genes. More importantly, the results demonstrated farnesol-induced upregulation of the caspase gene MCA1 and the intracellular presence of activated caspases. In conclusion, this study demonstrated that farnesol promotes apoptosis in C. albicans through caspase activation, implying an important physiological role for farnesol in the fungal cell life cycle with important implications for adaptation and survival.

Isozyme polymorphism of cellulases in Aspergillus terreus

Maximum cellulase production in Aspergillus terreus was obtained at a temperature of 28 degrees C, pH 4.0 and a substrate concentration of 1% CMC. Variability in cellulase enzyme production and isozyme polymorphism of endo-beta-1,4-glucanase and beta-1,4-glucosidase was studied in 45 natural isolates of A. terreus. Different electrophoretic patterns were evident for endoglucanase. Three zones of activity viz EG 1, EG 11 and EG 111 were observed showing different electrophoretic mobilities. Some of the isolates exhibited the presence of null alleles for EG 1. During development EG 1 and EG 11 were observed throughout while EG 111 appeared on the eighth day. For beta-1,4-glucosidase two zones of activity viz beta-glu 1 and beta-glu 11 were observed. beta-glu 1 showed variable electrophoretic mobilities. beta-glu 1 appeared throughout during development while beta-glu 11 appeared on the twelfth day.

Differential kinetic properties of L-2-amino-4-methylthio-cis-but-3-enoic acid, a methionine analog inhibitor of S-adenosylmethionine synthetase

The L-methionine analog, L-2-amino-4-methylthio-cis-but-3-enoic acid (L-cisAMTB), was examined as a potential inhibitor of the enzyme, S-adenosylmethionine (AdoMet) synthetase. The rational design of L-cisAMTB was based on previously observed potent enzyme inhibitory activity for its closely related structural analog, L-2-amino-4-methoxy-cis-but-3-enoic acid (L-cisAMB). The kinetic behavior of L-cisAMTB was studied using AdoMet synthetase isozymes I and II fractionated from L1210 murine leukemia cells. L-cisAMTB, which was a competitive inhibitor with respect to L-methionine, gave apparent Ki values of 21 and 5.7 microM for isozymes I and II, respectively. These values indicate that L-cisAMTB was slightly less inhibitory than L-cisAMB. L-cisAMTB was also a substrate for the AdoMet synthetase reaction, with respective Km values of 555 and 33 microM for isozymes I and II. In the absence of added inhibitors, the activity of isozyme II, but not isozyme I, was stimulated 2.5-fold by the presence of 10% DMSO. This preferential stimulation of isozyme II and the highly significant difference in Km values of L-cisAMTB for isozymes I and II point to possible physical differences in these tumor isozymes that were not apparent in earlier studies.

Methionine adenosyltransferase: structure and function

Methionine adenosyltransferase (MAT), a key enzyme in metabolism, catalyzes the synthesis of one of the most important and pivotal biological molecules, S-adenosyl-methionine. In every organism studied thus far, MAT exists in multiple forms; most are encoded by related, but distinct genes. Molecular and immunological studies revealed the presence of considerable conservation in the structure of MAT from different species; however, the various MAT isozymes differ in their physical and kinetic properties in ways that allow them to be regulated differently. Recent studies suggest that human MAT is composed of nonidentical subunits that can assume multiple states of aggregation, each with different kinetic characteristics. The tissue distribution of MAT isozymes and the ability of cells within the same tissue to switch between the different forms of MAT suggest that this mode of regulation is important for cellular function and differentiation. Therefore, understanding the regulation and structure-function relationship of this fascinating enzyme should help us clarify its role in biology and may provide us with tools to effectively manipulate its activity in clinical situations such as cancer, autoimmunity and organ transplantation.