Biology subjects

Kar, R. K.

Publications and source records attributed to Kar, R. K..

6 recordsLinked to original sources

bioRxiv2023

Computational prediction of gamma-oryzanol as potential agonist of human peroxisome proliferator-activated receptor gamma (ppar-γ)

Diabetes mellitus is one of the complex metabolic disorders associated with individuals leading sedentary lifestyles. It leads to several complications rendering the normal function of vital organs like heart, liver, kidney, eye and brain. Scientists and doctors across the globe are involved in research for understanding the complex genetics of this disorder and formulating newer therapeutics accordingly. The finding of potential chemical entities and their underlying agonists or antagonist activities significantly controls the disorder but with some consequences. Thus there is demand for natural compounds and indigenous treatment methods for controlling the disorder with least or no adverse consequences. In the current work we present computational prediction of gamma-oryzanol as potential agonist of human peroxisome proliferator-activated receptor gamma (PPAR-{gamma}). A group of four gamma-oryzanol compound structures reported in PubChem database were downloaded and docked in the ligand binding site of five different human PPAR-{gamma} structures reported in PDB database. It was observed that most of the gamma-oryzanol compounds occupied themselves in the ligand binding P1, P2, P3, P4 sites with similar orientations as that of co-crystal agonists. Their binding conformations were assisted by some reasonable docking scores (-7 to -11 kcal/mol) and hydrogen bond interactions with some important conserved amino acid residues lining the ligand binding site. Additionally we have done a comparative molecular dynamics studies to reveal the flexibility of gamma-oryzanol in the ligand binding site in comparison to the co-crystal agonist and a scaffold analysis using the structure of six agonists and gamma-oryzanol for fetching potential scaffolds which may helpful in designing of new chemical entities.

bioinformatics↗

bioRxiv2022

Network analysis of chromophore binding site in LOV domain

Photoreceptor proteins are versatile toolbox for developing biosensors for optogenetic applications. These molecular tools get activated upon illumination of blue light, which in turn offers a non-invasive method for gaining high spatiotemporal resolution and precise control of cellular signal transduction. The Light-Oxygen-Voltage (LOV) domain family of proteins is a well-recognized system for constructing optogenetic devices. Translation of these proteins into efficient cellular sensors is possible by tuning their photochemistry lifetime. However, the bottleneck is the need for more understanding of the relationship between the protein environment and photocycle kinetics. Significantly, the effect of the local environment also modulates the electronic structure of chromophore, which perturbs the electrostatic and hydrophobic interaction within the binding site. This work highlights the critical factors hidden in the protein networks, linking with their experimental photocycle kinetics. It presents an opportunity to quantitatively examine the alternation in chromophores equilibrium geometry and identify details which have substantial implications in designing synthetic LOV constructs with desirable photocycle efficiency.

bioengineering↗

bioRxiv2021

Cellular heterogeneity and MTH1 play key roles in galactose mediated signaling of the GAL switch to utilize the disaccharide melibiose

Yeast metabolizes the disaccharide melibiose by hydrolyzing it into equimolar concentrations of glucose and galactose by MEL1-encoded -galactosidase. Galactose metabolizing genes (including MEL1) are induced by galactose and repressed by glucose, which are the products of melibiose hydrolysis. Therefore, how melibiose catabolization and utilization take place by circumventing the glucose repression is an enigma. Other than the galactose metabolizing genes MTH1, a negative regulator of glucose signal pathway has Gal4p binding sites and is induced by galactose and repressed by high glucose concentration. But, at low or no glucose MTH1 along with its paralogue STD1 represses hexose transporters, that are involved in glucose transport. This sort of tuning of glucose and galactose regulation motivated us to delineate the role of MTH1 as a regulator of MEL1 expression and melibiose utilization. The deletion mutant of MTH1 shows growth defect on melibiose and this growth defect is enhanced upon the deletion of both MTH1 and its paralogue STD1. Microscopy and flowcytometry analysis, suggest, that even though MEL1 and GAL1 promoter are under Gal4p and Gal80p regulation, upon deletion of MTH1 it hampers only MEL1 expression, but not the GAL1 gene expression. By using 2-Deoxy galactose toxicity assay, we observed phenotypic heterogeneity in cells grown on melibiose i.e. after cleaving of melibiose a fraction of cell population utilizes glucose and another fraction utilizes galactose and coexist together. Understanding GAL/MEL gene expression patterns in melibiose will have great implication to understand various other complex sugar utilizations, tunable gene expressions and complex feedback gene regulations. SignificanceSugar metabolism is an important phenomenon to understand the regulation of gene expression. Glucose is the most preferred carbon source. Yeast follows glycolytic pathways like cancer cells for metabolism of sugars and understanding this will throw more light to the metabolism of cancer cells. In this communication we observed cell-to-cell heterogeneity in yeast cells playing a key role in metabolism of a complex disaccharide melibiose, which gets cleaved into glucose and galactose by -galactosidase. Glucose represses -galactosidase and galactose induces it. Because of the heterogeneous population of cells one fraction consumes glucose liberated by melibiose hydrolysis, therefore it is not sufficient to repress -galactosidase and other GAL genes. Therefore, GAL genes are expressed and help in metabolizing melibiose and galactose.

microbiology↗

bioRxiv2021

Neuron specific ablation of eIF5A or deoxyhypusine synthase leads to impairment in development and cognitive functions in mice

Eukaryotic initiation factor 5A (eIF5A) is an essential factor with a unique amino acid, hypusine, required for its activity. Hypusine is formed exclusively in eIF5A by a post-translational modification involving two enzymes, deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Each of the three genes, Eif5a, Dhps or Dohh is required for mouse embryonic development. Variants in EIF5A or DHPS were recently identified as the genetic basis underlying certain rare neurodevelopmental disorders in humans. To investigate the roles of eIF5A and DHPS in brain development, we have generated four conditional knockout mouse strains using the Emx1-Cre or Camk2a-Cre strain and examined the effects of temporal- and region-specific deletion of Eif5a or Dhps. The conditional deletion of Dhps or Eif5a by Emx1 promotor driven Cre expression (E.9.5, cortex and hippocampus) led to gross defects in forebrain development, reduced growth and premature death. On the other hand, the conditional deletion of Dhps or Eif5a by Camk2a-promoter driven Cre expression (postnatal, mainly in the CA1 region of hippocampus) did not lead to global developmental defects; rather, these knockout animals exhibited severe impairment in spatial learning, contextual learning and memory, when subjected to the Morris Water Maze test and a contextual learning test. In both models, the Dhps knockout mice displayed more severe impairment than their Eif5a knockout counterparts. The observed defects in brain, global development or cognitive functions most likely result from translation errors due to a deficiency in active, hypusinated eIF5A. Our study underscores the important roles of eIF5A and DHPS in neurodevelopment. SignificanceeIF5A, an essential translation factor, is the only protein that undergoes a unique posttranslational modification, that converts lysine to hypusine by conjugation of the aminobutyl moiety from the polyamine spermidine. Hypusine biosynthesis occurs by two enzymatic steps involving deoxyhypusine synthase (DHPS) and deoxyhypusine hydroxylase (DOHH). Mutations in EIF5A or DHPS have been associated with rare neurodevelopmental disorders in humans. To understand the mechanisms underlying the pathogenesis of the disease, we generated mutant mice with brain-specific deletions of Eif5a or Dhps. The Eif5a and Dhps conditional knockout mice exhibited impairment in brain development, growth and cognitive functions. These animal models may serve as useful tools in the development of therapies against the eIF5A- or DHPS-associated neurodevelopmental disorders.

neuroscience↗

bioRxiv2019

High resolution structure of a partially folded insulin aggregation intermediate

Insulin has long served as a model for protein aggregation, both because of the importance of aggregation in insulin manufacture and because the structural biology of insulin has been extensively characterized. Despite intensive study, details about the initial triggers for aggregation have remained elusive at the molecular level. We show here that at acidic pH, the aggregation of insulin is likely initiated by a partially folded monomeric intermediate whose concentration is controlled by an off-pathway micellar species. High resolution structures of the partially folded intermediate show that it is coarsely similar to the initial monomeric structure but differs in subtle details - the A chain helices on the receptor interface are more disordered and the B chain helix moves away from C-terminal A chain helix. The result of these movements is the creation of a hydrophobic cavity in the center of the protein that may serve as nucleation site for oligomer formation. Knowledge of this transition may aid in the engineering of insulin variants that retain the favorable pharamacokinetic properties of monomeric insulin but are more resistant to aggregation.

biophysics↗

bioRxiv2018

Non-productive Binding Modes as a Prominent Feature of Aβ1-40 Fiber Elongation: Insights from Molecular Dynamics Simulation

AbstractAmyloid formation has been implicated in a number of neurodegenerative diseases. The elongation of amyloid fibers is thermodynamically strongly favorable but kinetic traps exist where the incoming monomer binds in an incompatible conformation that blocks further elongation. Unfortunately, this process is difficult to follow experimentally at the atomic level. It is also too complex to simulate in full detail and thus so far has been explored either through coarse-grained simulations, which may miss many important interactions, or full atomic simulations in which the incoming peptide is constrained to be near the ideal fiber geometry. Here we use an alternate approach starting from a docked complex in which the monomer is from an experimental NMR structure of one of the major conformations in the unbound ensemble, a largely unstructured peptide with the central hydrophobic region in a 310 helix. A 1000 ns full atomic simulation in explicit solvent shows the formation of a metastable intermediate by sequential, concerted movements of both the fiber and monomer. A Markov state model shows the unfolded monomer is trapped at the end of the fiber in a set of interconverting anti-parallel {beta}-hairpin conformations. The simulation here may serve as a model for the binding of other non-{beta}-sheet conformations to amyloid fibers.

biophysics↗