MECHANISTIC STUDIES ON RADICAL S-ADENOSYL-L-METHIONINE ENZYMES INVOLVED IN MENAQUINONE, THIAMIN AND COBALAMIN BIOSYNTHESIS

Menaquinone (Vitamin K) is an electron transfer cofactor that is an essential component for all the domains of life. Recently discovered, futalosine-dependent menaquinone biosynthetic pathway uses radical chemistry to assemble the aromatic core of menaquinone. Aminofutalosine synthase (MqnE)- a radical S-Adenosylmethionine (SAM) enzyme, catalyzes the key C-C bond formation reaction in this pathway converting 3-((1-carboxyvinyl)oxy)benzoic acid to Aminofutalosine. We have proposed a novel reaction mechanism for the MqnE catalyzed radical rearrangement involving a radical addition to the stable benzene ring. In support of this mechanism, we have successfully trapped the captodative and aryl radical anion intermediates using intramolecular, fast and radical triggered carbon-halogen bond fragmentation reactions (b-scission and SRN1 fragmentation). We have utilized exogenous radical trapping agents such as 5,5-dimethyl-1- pyrroline-N- oxide (DMPO), and sodium dithionite to trap radical intermediates in MqnE catalyzed reaction as a DMPO-spin adduct and sulfinate adduct respectively. We also have developed a chemical derivatization strategy for these sulfinate adducts to facilitate their chromatographic detection under aerobic conditions. These radical trapping strategies are generally useful in the study of other transient enzymatic radicals. Using a mechanism-guided approach, we have identified potent inhibitors of MqnE and have demonstrated their inhibitory activity against important human pathogens - Helicobacter pylori and Campylobacter jejuni. The best inhibitor exhibits tight-binding inhibition kinetics and has comparable antibacterial to currently approved antibiotics in the treatment of H. pylori infections. Thiamin Pyrimidine Synthase (ThiC) and its paralog- hydroxybenzimidazole Synthase (BzaF) play a pivotal role in the biosynthesis of thiamin (Vitamin B1) and cobalamin (Vitamin B12) by converting 5-aminoimidazole ribonucleotide (AIR) to hydroxymethyl pyrimidine phosphate (HMP-P) and 5- hydroxybenzimidazole (5-HBI) respectively. ThiC catalyzes the most complex unresolved radical rearrangement in primary metabolism. We have used rationally designed substrate analogs to study early steps of the ThiC and BzaF catalyzed reactions and have trapped a ribose based radical intermediate in the form of a sulfinate adduct using sodium dithionite as a trapping agent. These studies have demonstrated that ThiC and BzaF reactions follow a fragmentation-recombination mechanism and have enabled us to propose credible mechanistic hypotheses for these unprecedented transformations

MECHANISTIC STUDIES ON RADICAL S-ADENOSYL-L-METHIONINE ENZYMES INVOLVED IN MENAQUINONE, THIAMIN AND COBALAMIN BIOSYNTHESIS

Menaquinone (Vitamin K) is an electron transfer cofactor that is an essential component for all the domains of life. Recently discovered, futalosine-dependent menaquinone biosynthetic pathway uses radical chemistry to assemble the aromatic core of menaquinone. Aminofutalosine synthase (MqnE)- a radical S-Adenosylmethionine (SAM) enzyme, catalyzes the key C-C bond formation reaction in this pathway converting 3-((1-carboxyvinyl)oxy)benzoic acid to Aminofutalosine. We have proposed a novel reaction mechanism for the MqnE catalyzed radical rearrangement involving a radical addition to the stable benzene ring. In support of this mechanism, we have successfully trapped the captodative and aryl radical anion intermediates using intramolecular, fast and radical triggered carbon-halogen bond fragmentation reactions (b-scission and SRN1 fragmentation). We have utilized exogenous radical trapping agents such as 5,5-dimethyl-1- pyrroline-N- oxide (DMPO), and sodium dithionite to trap radical intermediates in MqnE catalyzed reaction as a DMPO-spin adduct and sulfinate adduct respectively. We also have developed a chemical derivatization strategy for these sulfinate adducts to facilitate their chromatographic detection under aerobic conditions. These radical trapping strategies are generally useful in the study of other transient enzymatic radicals. Using a mechanism-guided approach, we have identified potent inhibitors of MqnE and have demonstrated their inhibitory activity against important human pathogens - Helicobacter pylori and Campylobacter jejuni. The best inhibitor exhibits tight-binding inhibition kinetics and has comparable antibacterial to currently approved antibiotics in the treatment of H. pylori infections. Thiamin Pyrimidine Synthase (ThiC) and its paralog- hydroxybenzimidazole Synthase (BzaF) play a pivotal role in the biosynthesis of thiamin (Vitamin B1) and cobalamin (Vitamin B12) by converting 5-aminoimidazole ribonucleotide (AIR) to hydroxymethyl pyrimidine phosphate (HMP-P) and 5- hydroxybenzimidazole (5-HBI) respectively. ThiC catalyzes the most complex unresolved radical rearrangement in primary metabolism. We have used rationally designed substrate analogs to study early steps of the ThiC and BzaF catalyzed reactions and have trapped a ribose based radical intermediate in the form of a sulfinate adduct using sodium dithionite as a trapping agent. These studies have demonstrated that ThiC and BzaF reactions follow a fragmentation-recombination mechanism and have enabled us to propose credible mechanistic hypotheses for these unprecedented transformations

Quantifying three dimensional effects in acoustic rough surface scattering

textInterface roughness can have a significant effect on the scattering of sound energy, and therefore an understanding of the effects of roughness is essential to making predictions of sound propagation and transmission underwater. Many models of roughness scattering currently in use are two dimensional (2D) in nature; three dimensional (3D) modeling requires significantly more time and computational resources. In this work, an effort is made to quantify the effects of 3D scattering in order to assess whether or under what conditions 3D modeling is necessary. To that end, an exact 3D roughness scattering model is developed based on a commercially available finite element package. The finite element results are compared with two approximate scattering models (the Kirchhoff approximation and first order perturbation theory) to establish the validity and regimes of applicability of each. The rough surfaces are realizations generated from power spectra measured from the sea floor. However, the surfaces are assumed to be pressure release (as on an air-water interface). Such a formulation is nonphysical, but allows the assessment of the validity of the various modeling techniques which is the focus of this work. The comparison between the models is made by calculating the ensemble average of the scattering from realizations of randomly rough surfaces. It is shown that a combination of the Kirchhoff approximation and perturbation theory models recovers the 3D finite element solution.Mechanical Engineerin

Therapeutic efficacy of Guduchi w.s.r to Madhyama Khanda of Sharangdhar Samhita

Various classics of Ayurveda has many herbs which are highly praised for their high therapeutic values, versatile range of action and easy availability. Along with the use of single herb in the therapy, use of various formulations in the form of Panchavidha Kashaya Kalpana is also indicated in the treatment of various diseases. Guduchi, botanically identified as Tinospora cordifolia (Wild.) Miers. of family, Menispermaceae is one such highly praised drug by almost all scholars. Guduchi is known by various names like Amruta, Chhinna, Chhinnaruha, Chakra, Chakralakshanika, Dhara, Somavalli etc. It has been indicated in management of Jwara (Pyrexia), Vatarakta (Joint disorders), Kushtha (Skin diseases), Kamala (Jaundice) and many other systemic disorders. Sharangdhar Samnhita is one of the important treatise on Bhaishajya Kalpana (Ayurvedic pharmaceutics). Madhyam Khanda of Sharangdhar Samhita is designed for description of various formulations. It contains dedicated chapter according to the type of formulations like Swaras. Kwatha, Hima etc. As like other scholars, Sharangdhar has also praised Guduchi for its higher therapeutic efficacy. Hence, it is needed to review the Madhyam Khanda of Sharangghar Samhita for knowing the use of Guduchi in variety of formulations

Stock Price Prediction using Facebook Prophet

Estimating stock prices has always been a challenging task for researchers in the financial sector. Although the Efficient Market Hypothesis states that it is impossible to accurately predict stock prices, there is work in the literature that has shown that stock price movements can be predicted with the right level of accuracy, if the right variables are selected and appropriate predictor models are developed. those that are flexible. The Stock Market is volatile in nature and the prediction of the same is a cumbersome task. Stock prices depend upon not only economic factors, but they relate to various physical, psychological, rational and other important parameters. In this research work, the stock prices are predicted using Facebook Prophet. Stock price predictive models have been developed and run-on published stock data acquired from Yahoo Finance. Prophet is capable of generating daily, weekly and yearly seasonality along with holiday effects, by implementing regression models. The experimental results lead to the conclusion that Facebook Prophet can be used to predict stock prices for a long period of time with reasonable accuracy

Radical SAM Enzyme HydE Generates Adenosylated Fe(I) Intermediates En Route to the [FeFe]-Hydrogenase Catalytic H‑Cluster

The H-cluster of [FeFe]-hydrogenase consists of a [4Fe-4S]H-subcluster linked by a cysteinyl bridge to a unique organometallic [2Fe]H-subcluster assigned as the site of interconversion between protons and molecular hydrogen. This [2Fe]H-subcluster is assembled by a set of Fe-S maturase enzymes HydG, HydE and HydF. Here we show that the HydG product [FeII(Cys)(CO)2(CN)] synthon is the substrate of the radical SAM enzyme HydE, with the generated 5'-deoxyadenosyl radical attacking the cysteine S to form a C5'-S bond concomitant with reduction of the central low-spin Fe(II) to the Fe(I) oxidation state. This leads to the cleavage of the cysteine C3-S bond, producing a mononuclear [FeI(CO)2(CN)S] species that serves as the precursor to the dinuclear Fe(I)Fe(I) center of the [2Fe]H-subcluster. This work unveils the role played by HydE in the enzymatic assembly of the H-cluster and expands the scope of radical SAM enzyme chemistry