Ram A. Vishwakarma

Nanoclusters of GPI-Anchored Proteins Are Formed by Cortical Actin-Driven Activity

Several cell-surface lipid-tethered proteins exhibit a concentration-independent, cholesterol-sensitive organization of nanoscale clusters and monomers. To understand the mechanism of formation of these clusters, we investigate the spatial distribution and steady-state dynamics of fluorescently tagged GPI-anchored protein nanoclusters using high-spatial and temporal resolution FRET microscopy. These studies reveal a nonrandom spatial distribution of nanoclusters, concentrated in optically resolvable domains. Monitoring the dynamics of recovery of fluorescence intensity and anisotropy, we find that nanoclusters are immobile, and the dynamics of interconversion between nanoclusters and monomers, over a range of temperatures, is spatially heterogeneous and non-Arrhenius, with a sharp crossover coinciding with a reduction in the activity of cortical actin. Cholesterol depletion perturbs cortical actin and the spatial scale and interconversion dynamics of nanoclusters. Direct perturbations of cortical actin activity also affect the construction, dynamics, and spatial organization of nanoclusters. These results suggest a unique mechanism of complexation of cell-surface molecules regulated by cortical actin activity.

Transbilayer Lipid Interactions Mediate Nanoclustering of Lipid-Anchored Proteins

Understanding how functional lipid domains in live cell membranes are generated has posed a challenge. Here, we show that transbilayer interactions are necessary for the generation of cholesterol-dependent nanoclusters of GPI-anchored proteins mediated by membrane-adjacent dynamic actin filaments. We find that long saturated acyl-chains are required for forming GPI-anchor nanoclusters. Simultaneously, at the inner leaflet, long acyl-chain-containing phosphatidylserine (PS) is necessary for transbilayer coupling. All-atom molecular dynamics simulations of asymmetric multicomponent-membrane bilayers in a mixed phase provide evidence that immobilization of long saturated acyl-chain lipids at either leaflet stabilizes cholesterol-dependent transbilayer interactions forming local domains with characteristics similar to a liquid-ordered (lo) phase. This is verified by experiments wherein immobilization of long acyl-chain lipids at one leaflet effects transbilayer interactions of corresponding lipids at the opposite leaflet. This suggests a general mechanism for the generation and stabilization of nanoscale cholesterol-dependent and actin-mediated lipid clusters in live cell membranes.

Metal-Free Oxidative Amidation of 2-Oxoaldehydes: A Facile Access to α-Ketoamides

A novel and efficient method for the synthesis of α-ketoamides, employing a dimethyl sulfoxide (DMSO)-promoted oxidative amidation reaction between 2-oxoaldehydes and amines under metal-free conditions is presented. Furthermore, mechanistic studies supported an iminium ion-based intermediate as a central feature of reaction wherein C1-oxygen atom of α-ketoamides is finally derived from DMSO.

Progress in the discovery and development of small-molecule modulators of G-protein-coupled receptor 40 (GPR40/FFA1/FFAR1): an emerging target for type 2 diabetes

Background: The family of G-protein-coupled receptors (GPCRs) serves as the target for almost a third of currently marketed drugs and provides the predominant mechanism through which extracellular factors transmit signals to the cell. GPCRs have been proved to be good therapeutic targets for metabolic disorders. In recent years, a number of companies have been actively involved in the discovery of small-molecule modulators of the GPR40 (FFA1) receptor. However, to date, no critical, comprehensive review on small-molecule modulators of GPR40 (FFA1) has been published. Objective: To review the discovery and development of small-molecule GPR40 (FFA1) agonists/antagonists by different research groups and to classify them based on the key structural features. Method: Systematic search, analysis, and summary of the publication and patent literature for small-molecule modulators of the GPR40 (FFA1) receptor to June 2008. The patent information for this review is drawn from the Integrity Prous, Scifinder, Esp@cenet, and freepatentonline.com databases. Conclusion: The para-substituted phenyl propionic acid scaffold has emerged as a common structural motif found in many GPR40 (FFA1) agonists, and compounds having an aromatic ring and a group capable of releasing a cation have exhibited excellent GPR40 (FFA1) agonistic activity. Several small-molecule agonists of GPR40 (FFA1) have been discovered, which offer a great promise in the treatment of type 2 diabetes.

Iron-catalyzed Cross-Coupling of Electron-Deficient Heterocycles and Quinone with Organoboron Species via Innate C–H Functionalization: Application in Total Synthesis of Pyrazine Alkaloid Botryllazine A

Here, we report an iron-catalyzed cross-coupling reaction of electron-deficient heterocycles and quinone with organoboron species via innate C-H functionalization. Iron(II) acetylacetonate along with oxidant (K2S2O8) and phase-transfer catalyst (TBAB) under open flask conditions efficiently catalyzed the cross-coupling of pyrazine with arylboronic acids and gave monoarylated products in good to excellent yields. Optimized conditions also worked for other heterocylces such as quinoxalines, pyridines, quinoline, and isoquinoline as well as quinones. In addition, we demonstrated as a first example its application for the synthesis of anticancer marine pyrazine alkaloid botryllazine A.

Effect of Emblica officinalis (fruit) against UVB-induced photo-aging in human skin fibroblasts.

ETHNOPHARMACOLOGICAL RELEVANCE Emblica officinalis fruit (EO), commonly known as Amla is a reputed traditional medicine and functional food used in Indian subcontinent. It has long been used in Indian folk medicine to treat liver diseases, stomach ulcers, inflammatory diseases, metabolic disorders, geriatric complaints, skin disorders and beauty care. AIM OF THE STUDY Recently, it has been shown to promote pro-collagen content and inhibit matrix metalloproteinase levels in skin fibroblast. The aim of the present study was to investigate the efficacy of EO to inhibit UVB-induced photo-aging in human skin fibroblasts. MATERIALS AND METHODS Mitochondrial activity of human skin fibroblasts was measured by MTT-assay. Quantifications of pro-collagen 1 and matrix metalloproteinase 1 (MMP-1) release were performed by immunoassay techniques. Hyaluronidase inhibition assay was studied in vitro using bovine testicular hyaluronidase and human umbilical cord hyaluronic acid. Cell cycle analysis was performed by flowcytometry using propidium iodide. RESULTS EO stimulated, the otherwise UVB inhibited cellular proliferation and protected pro-collagen 1 against UVB-induced depletion via inhibition of UVB-induced MMP-1 in skin fibroblasts (10-40 μg/mL, p>0.001). EO exhibited inhibitory activity of hyaluronidase (10-40 μg/mL, p>0.001). Treatment with EO also prevented UVB disturbed cell cycle to normal phase. CONCLUSION The results of the present study suggests that EO effectively inhibits UVB-induced photo-aging in human skin fibroblast via its strong ROS scavenging ability and its therapeutic and cosmetic applications remain to be explored.

Requirement of the mymA Operon for Appropriate Cell Wall Ultrastructure and Persistence of Mycobacterium tuberculosis in the Spleens of Guinea Pigs

We had recently reported that the mymA operon (Rv3083 to Rv3089) of Mycobacterium tuberculosis is regulated by AraC/XylS transcriptional regulator VirS (Rv3082c) and is important for the cell envelope of M. tuberculosis. In this study, we further show that a virS mutant (MtbdeltavirS) and a mymA mutant (Mtbmym::hyg) of M. tuberculosis exhibit reduced contents and altered composition of mycolic acids along with the accumulation of saturated C24 and C26 fatty acids compared to the parental strain. These mutants were markedly more susceptible to major antitubercular drugs at acidic pH and also showed increased sensitivity to detergent (sodium dodecyl sulfate) and to acidic stress than the parental strain. We show that disruption of virS and mymA genes impairs the ability of M. tuberculosis to survive in activated macrophages, but not in resting macrophages, suggesting the importance of the mymA operon in protecting the bacterium against harsher conditions. Infection of guinea pigs with MtbdeltavirS, Mtbmym::hyg, and the parental strain resulted in an approximately 800-fold-reduced bacillary load of the mutant strains compared with the parental strain in spleens, but not in the lungs, of animals at 20 weeks postinfection. Phenotypic traits were fully complemented upon reintroduction of the virS gene into MtbdeltavirS. These observations show the important role of the mymA operon in the pathogenesis of M. tuberculosis at later stages of the disease.

Molecular cloning, bacterial expression and promoter analysis of squalene synthase from Withania somnifera (L.) Dunal

Withania somnifera (ashwagandha) is a rich repository of large number of pharmacologically active secondary metabolites known as withanolides. Though the plant has been well characterized in terms of phytochemical profiles as well as pharmaceutical activities, but there is sparse information about the genes responsible for biosynthesis of these compounds. In this study, we have cloned and characterized a gene encoding squalene synthase (EC 2.5.1.21) from a withaferin A rich variety of W. somnifera, a key enzyme in the biosynthesis of isoprenoids. Squalene synthase catalyses dimerization of two farnesyl diphosphate (FPP) molecules into squalene, a key precursor for sterols and triterpenes. A full-length cDNA consisting of 1765 bp was isolated and contained a 1236 bp open reading frame (ORF) encoding a polypeptide of 411 amino acids. Recombinant C-terminus truncated squalene synthase (WsSQS) was expressed in BL21 cells (Escherichia coli) with optimum expression induced with 1mM IPTG at 37°C after 1h. Quantitative RT-PCR analysis showed that squalene synthase (WsSQS) expressed in all tested tissues including roots, stem and leaves with the highest level of expression in leaves. The promoter region of WsSQS isolated by genome walking presented several cis-acting elements in the promoter region. Biosynthesis of withanolides was up-regulated by different signalling components including methyl-jasmonate, salicylic acid and 2, 4-D, which was consistent with the predicted results of WsSQS promoter region. This work is the first report of cloning and expression of squalene synthase from W. somnifera and will be useful to understand the regulatory role of squalene synthase in the biosynthesis of withanolides.

Metal-free domino one-pot protocols for quinoline synthesis

Quinoline is one of the most widely investigated scaffolds by synthetic chemists because of its medicinal importance. A wide range of metal-catalyzed, metal-free, multi-step or domino one-pot protocols are reported in the literature for construction of this scaffold. Several reviews have appeared on synthetic aspects of this scaffold, however there is no focused review on metal-free domino one-pot protocols. Domino one-pot protocols offer an opportunity to access highly functionalized final products from simple starting materials. Because of this unique feature of domino protocols, in recent years their utility for generation of molecular libraries has been widely appreciated. In this review, all contributions till March 2015 are surveyed with particular emphasis on metal-free domino reactions for quinoline ring construction and are discussed herein along with mechanistic aspects.

Anti-inflammatory and anticancer activity of ergoflavin isolated from an endophytic fungus.

Biodiversity is a major resource for identification of new molecules with specific therapeutic activities. To identify such an active resource, high throughput screening (HTS) of the extracts prepared from such diversity are examined on specific functional assays. Based on such HTS studies and bioactivity-based fractionation, we have isolated ergoflavin, a pigment from an endophytic fungus, growing on the leaves of an Indian medicinal plant Mimosops elengi (bakul). We report here the isolation, structure elucidation, and biological properties of this compound, which showed good anti-inflammatory and anticancer activities.