Msh2-Msh3 interferes with Okazaki fragment processing to promote trinucleotide repeat expansions

Trinucleotide repeat (TNR) expansions are the underlying cause of more than 40 neurodegenerative and neuromuscular diseases, including myotonic dystrophy and Huntington's disease. Although genetic evidence points to errors in DNA replication and/or repair as the cause of these diseases, clear molecular mechanisms have not been described. Here, we focused on the role of the mismatch repair complex Msh2-Msh3 in promoting TNR expansions. We demonstrate that Msh2-Msh3 promotes CTG and CAG repeat expansions in vivo in Saccharomyces cerevisiae. Furthermore, we provide biochemical evidence that Msh2-Msh3 directly interferes with normal Okazaki fragment processing by flap endonuclease1 (Rad27) and DNA ligase I (Cdc9) in the presence of TNR sequences, thereby producing small, incremental expansion events. We believe that this is the first mechanistic evidence showing the interplay of replication and repair proteins in the expansion of sequences during lagging-strand DNA replication.     

Decreased GABA receptor in the cerebral cortex of epileptic rats: effect of Bacopa monnieri and Bacoside-A

Abstact

Background

Gamma amino butyric acid (GABA), the principal inhibitory neurotransmitter in the cerebral cortex, maintains the inhibitory tones that counter balances neuronal excitation. When this balance is perturbed, seizures may ensue.

Methods

In the present study, alterations of the general GABA, GABA_A and GABA_B receptors in the cerebral cortex of the epileptic rat and the therapeutic application of Bacopa monnieri were investigated.

Results

Scatchard analysis of [³H]GABA, [³H]bicuculline and [³H]baclofen in the cerebral cortex of the epileptic rat showed significant decrease in B_max (P < 0.001) compared to control. Real Time PCR amplification of GABA receptor subunits such as GABA_Aά1, GABA_Aγ, GABA_Aδ, GABA_B and GAD where down regulated (P < 0.001) in epileptic rats. GABA_Aά5 subunit and Cyclic AMP responsible element binding protein were up regulated. Confocal imaging study confirmed the decreased GABA receptors in epileptic rats. Epileptic rats have deficit in radial arm and Y maze performance.

Conclusions

Bacopa monnieri and Bacoside-A treatment reverses epilepsy associated changes to near control suggesting that decreased GABA receptors in the cerebral cortex have an important role in epileptic occurrence; Bacopa monnieri and Bacoside-A have therapeutic application in epilepsy management.     

Direct cell penetration of the antifungal peptide,MMGP1, in Candida albicans

An antifungal peptide, MMGP1, was recently identified from marine metagenome. The mechanism of cellular internalization of this peptide in Candida albicans was studied using fluorescein 5–isothiocynate (Sigma, California, USA) labeling followed by fluorescence microscopy and flow cytometry analyses. The peptide could enter C. albicans cells even at 4 °C, where all energy‐dependent transport mechanisms are blocked. In addition, the peptide internalization was not affected by the endocytic inhibitor, sodium azide. The kinetic study has shown that the peptide was initially localized on cell membrane and subsequently internalized into cytosol. The MMGP1 treatment exhibited time‐dependent cytotoxicity in C. albicans as evidenced by SYTOX Green (Molecular Probes Inc., Eugene, Oreg) uptake. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Functional and Molecular Characterization of the Role of CTCF in Human Embryonic Stem Cell Biology

The CCCTC-binding factor CTCF is the only known vertebrate insulator protein and has been shown to regulate important developmental processes such as imprinting, X-chromosome inactivation and genomic architecture. In this study, we examined the role of CTCF in human embryonic stem cell (hESC) biology. We demonstrate that CTCF associates with several important pluripotency genes, including NANOG, SOX2, cMYC and LIN28 and is critical for hESC proliferation. CTCF depletion impacts expression of pluripotency genes and accelerates loss of pluripotency upon BMP4 induced differentiation, but does not result in spontaneous differentiation. We find that CTCF associates with the distal ends and internal sites of the co-regulated 160 kb NANOG-DPPA3-GDF3 locus. Each of these sites can function as a CTCF-dependent enhancer-blocking insulator in heterologous assays. In hESCs, CTCF exists in multisubunit protein complexes and can be poly(ADP)ribosylated. Known CTCF cofactors, such as Cohesin, differentially co-localize in the vicinity of specific CTCF binding sites within the NANOG locus. Importantly, the association of some cofactors and protein PARlation selectively changes upon differentiation although CTCF binding remains constant. Understanding how unique cofactors may impart specialized functions to CTCF at specific genomic locations will further illuminate its role in stem cell biology.     

Designing of Protein Kinase C β-II Inhibitors against Diabetic complications: Structure Based Drug Design, Induced Fit docking and analysis of active site conformational changes

Protein Kinase C β-II (PKC β-II) is an important enzyme in the development of diabetic complications like cardiomyopathy, retinopathy, neuropathy, nephropathy and angiopathy. PKC β-II is activated in vascular tissues during diabetic vascular abnormalities. Thus, PKC β-II is considered as a potent drug target and the crystal structure of the kinase domain of PKC β-II (PDB id: 2I0E) was used to design inhibitors using Structure-Based Drug Design (SBDD) approach. Sixty inhibitors structurally similar to Staurosporine were retrieved from PubChem Compound database and High Throughput Virtual screening (HTVs) was carried out with PKC β-II. Based on the HTVs results and the nature of active site residues of PKC β-II, Staurosporine inhibitors were designed using SBDD. Induced Fit Docking (IFD) studies were carried out between kinase domain of PKC β-II and the designed inhibitors. These IFD complexes showed favorable docking score, glide energy, glide emodel and hydrogen bond and hydrophobic interactions with the active site of PKC β-II. Binding free energy was calculated for IFD complexes using Prime MM-GBSA method. The conformational changes induced by the inhibitor at the active site of PKC β-II were observed for the back bone Cα atoms and side-chain chi angles. PASS prediction tool was used to analyze the biological activities for the designed inhibitors. The various physicochemical properties were calculated for the compounds. One of the designed inhibitors successively satisfied all the in silico parameters among the others and seems to be a potent inhibitor against PKC β-II.     

Differentiation of sheeppox and goatpox viruses by polymerase Chain reaction-restriction fragment length polymorphism

In the present study, the partial gene sequences of P32 protein, an immunogenic envelope protein of Capripoxviruses (CaPV), were analyzed to assess the genetic relationship among sheeppox and goatpox virus isolates, and restriction enzyme specific PCR-RFLP was developed to differentiate CaPV strains. A total of six goatpox virus (GTPV) and nine sheeppox virus (SPPV) isolates of Indian origin were included in the sequence analysis of the attachment gene. The sequence analysis revealed a high degree of sequence identity among all the Indian SPPV and GTPV isolates at both nucleotide and amino acid levels. Phylogenetic analysis showed three distinct clusters of SPPV, GTPV and Lumpy skin disease virus (LSDV) isolates. Further, multiple sequence alignment revealed a unique change at G120A in all GTPV isolates resulting in the formation of Dra I restriction site in lieu of EcoR I, which is present in SPPV isolates studied. This change was unique and exploited to develop restriction enzyme specific PCR-RFLP for detection and differentiation of SPPV and GTPV strains. The optimized PCR-RFLP was validated using a total of fourteen (n=14) cell culture isolates and twenty two (n=22) known clinical samples of CaPV. The Restriction Enzyme specific PCR-RFLP to differentiate both species will allow a rapid differential diagnosis during CaPV outbreaks particularly in mixed flocks of sheep and goats and could be an adjunct/supportive tool for complete gene or virus genome sequencing methods.     

Substrate-triggered recruitment of the TolC channel-tunnel during type I export of hemolysin by Escherichia coli.

A defining event in type I export of hemolysin by Escherichia coli is the substrate-triggered recruitment of the TolC channel-tunnel by an inner membrane complex. This complex comprises a traffic ATPase (HlyB) and the 478 residue adaptor protein (HlyD), which contacts TolC during recruitment. HlyD has a large periplasmic domain (amino acid residues 81-478) linked by a single transmembrane helix to a small N-terminal cytosolic domain (1-59). Export was disabled by deletion of the ca 60 amino acid residue cytosolic domain of HlyD, even though the truncated HlyD (HlyDDelta45) was, like the wild-type, able to trimerise in the cytosolic membrane, and interact with the traffic ATPase. The mutant HlyB/HlyDDelta45 inner membrane complex engaged the hemolysin substrate, but this substrate-engaged complex failed to trigger recruitment of TolC. Further analyses showed that HlyDDelta45 was specifically unable to bind the substrate. The result suggests that substrate engagement by the traffic ATPase alone is insufficient to trigger TolC recruitment, and that substrate binding to the HlyD cytosolic domain is essential. Analysis of three further N-terminal deletion variants, HlyDDelta26, HlyDDelta26-45 and HlyDDelta34-38, indicated that an extreme N-terminal amphipathic helix and a cytosolic cluster of charged residues are central to the cytosolic domain function. The cytosolic amphipathic helix was not essential for substrate engagement or TolC recruitment, but export was impaired without it. In contrast, when the charged amino acid residues were deleted, the substrate was still engaged by HlyD but engagement was unproductive, i.e. TolC recruitment was not triggered. Our results are compatible with the HlyD cytosolic domain mediating transduction of the substrate binding signal directly, presumably to the HlyD periplasmic domain, to trigger recruitment of TolC and assemble the type I export complex.