A genetic network that balances two outcomes utilizes asymmetric recognition of operator sites.

Stability and induction of the lysogenic state of bacteriophage λ are balanced by a complex regulatory network. A key feature of this network is the mutually exclusive cooperative binding of a repressor dimer (CI) to one of two pairs of binding sites, O(R)1-O(R)2 or O(R)2-O(R)3. The structural features that underpin the mutually exclusive binding mode are not well understood. Recent studies have demonstrated that CI is an asymmetric dimer. The functional importance of the asymmetry is not fully clear. Due to the asymmetric nature of the CI dimer as well as its binding sites, there are two possible bound orientations. By fluorescence resonance energy transfer measurements we showed that CI prefers one bound orientation. We also demonstrated that the relative configuration of the binding sites is important for CI dimer-dimer interactions and consequent cooperative binding. We proposed that the operator configuration dictates the orientations of the bound CI molecules, which in turn dictates CI cooperative interaction between the O(R)1-O(R)2 or O(R)2-O(R)3, but not both. Modeling suggests that the relative orientation of the C- and N-terminal domains may play an important role in the mutually exclusive nature of the cooperative binding. This work correlates unique structural features of a transcription regulatory protein with the functional properties of a gene regulatory network.

Role of nano curcumin on superoxide dismutase levels in leukoplakia.

Introduction: Oral leukoplakia has an estimated prevalence of 2% of the oral cavity, one of the risk factors for oral cancers. The most commonly linked etiology being tobacco smoking causing reactive oxygen species (ROS) induced DNA damage. Curcumin, a polyphenol derivative from herbal remedy, possesses diverse properties ranging from centuries old documented anti-inflammatory properties to recently documented anticancer properties. Aims: Role of nano curcumin on superoxide dismutase (SOD) levels in leukoplakia patients' pre- and post-treatment. Materials and Methods: The study group comprised thirty test subjects. Single capsule of 250 mg (Brecan Plus) was given to the test group for 30 days with weekly follow-up. Blood samples were taken from the test group and were evaluated for SOD levels before and after the completion of the trial. Results: In the study, there was a decrease in size of the lesion, number of lesions, down staging of the disease, and increase in serum SOD levels after the therapy. Binary logistic retrogression analysis was done to assess the predictive ability of serum SOD-dependent variable, and a positive association was noted between increase in serum SOD level and down staging of the disease. Conclusion: Nano curcumin is an excellent medical nutrition intervention derived from traditional natural products. The study has demonstrated the clinical efficacy of these new classes of therapeutic nutraceuticals such as nanocurcumin in treating oral leukoplakia, which are suitable for long-term use.

Characterization of kinetics of DNA strand-exchange and ATP hydrolysis activities of recombinant PfRad51, a Plasmodium falciparum recombinase.

Although homologous recombination-mediated DNA rearrangements are quite widespread in Plasmodium falciparum, the molecular mechanisms involved are essentially unknown. Recent identification of PfRad51 in P. falciparum has suggested that it may play central role during homologous recombination and DNA rearrangements. Full-length recombinant PfRad51 was over expressed in Escherichia coli and purified to near homogeneity. Using optimized enzymatic activity conditions recombinant PfRad51 protein was shown to catalyze DNA strand-exchange reaction, a central step during homologous recombination. Unlike bacterial RecA protein, PfRad51 promoted strand-exchange reaction does not require ATP hydrolysis. The PfRad51 protein also catalyzed ssDNA-dependent ATP hydrolysis and the k(cat) values were similar to those reported for human Rad51. The demonstration of strand-exchange activity of PfRad51 protein, first such report in any protozoan parasite, suggests importance of similar recombination mechanism during DNA rearrangements associated with antigenic variation in P. falciparum.

Half-of-the-sites reactivity of F235C lambda-repressor: implications for the structure of the whole repressor.

A site-directed mutation, F235C, was created at the penultimate residue of the lambda-repressor. Measurement of dimer-monomer dissociation constant suggested that dimer-monomer dissociation of the mutant repressor is similar to that of the wild-type. Affinity towards a single operator O(R)1 is also similar to that of the wild-type repressor. The mutant repressor gene in a multi-copy plasmid confers immunity towards infection by a cI(-) lambda phage, suggesting preservation of functional integrity. Far-UV circular dichroism spectra show no major change in the secondary structure. Fluorescence quenching experiments, however, suggest increased exposure of some tryptophan residues. The urea denaturation profile indicates decreased stability of a part of the C-terminal domain. Under non-denaturing conditions, cysteine-235 shows half-of-the-sites reactivity, i.e. on average only one out of two cysteine-235 residues in the dimer shows reactivity towards sulfhydryl reagents. Fluorescence energy transfer between randomly labeled donor and acceptor fluorescent probes indicates that only one sulfhydryl per dimer is reactive, suggesting true half-of-the-sites reactivity. The structural role of the C-terminal tail in the whole repressor dimer is discussed.