Sathyanarayana N. Gummadi

Bio: Sathyanarayana N. Gummadi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Phospholipid scramblase & Caffeine. The author has an hindex of 25, co-authored 139 publications receiving 2332 citations. Previous affiliations of Sathyanarayana N. Gummadi include Indian Institutes of Technology & University of Wisconsin-Madison.

Crystal structure of yeast xylose reductase in complex with a novel NADP-DTT adduct provides insights into substrate recognition and catalysis

Abstract: Aldose reductases (ARs) belonging to the aldo-keto reductase (AKR) superfamily catalyze the conversion of carbonyl substrates into their respective alcohols. Here we report the crystal structures of the yeast Debaryomyces nepalensis xylose reductase (DnXR, AKR2B10) in the apo form and as a ternary complex with a novel NADP-DTT adduct. Xylose reductase, a key enzyme in the conversion of xylose to xylitol, has several industrial applications. The enzyme displayed the highest catalytic efficiency for l-threose (138 ± 7 mm-1 ·s-1 ) followed by d-erythrose (30 ± 3 mm-1 ·s-1 ). The crystal structure of the complex reveals a covalent linkage between the C4N atom of the nicotinamide ring of the cosubstrate and the S1 sulfur atom of DTT and provides the first structural evidence for a protein mediated NADP-low-molecular-mass thiol adduct. We hypothesize that the formation of the adduct is facilitated by an in-crystallo Michael addition of the DTT thiolate to the specific conformation of bound NADPH in the active site of DnXR. The interactions between DTT, a four-carbon sugar alcohol analog, and the enzyme are representative of a near-cognate product ternary complex and provide significant insights into the structural basis of aldose binding and specificity and the catalytic mechanism of ARs. DATABASE: Structural data are available in the PDB under the accession numbers 5ZCI and 5ZCM.

Growth of Halotolerant Food Spoiling Yeast Debaryomyces nepalensis NCYC 3413 Under the Influence of pH and Salt

Abstract: Debaryomyces nepalensis, a halotolerant food-spoiling yeast could grow in complex (YEPD) medium at different pHs ranging between 3.0 and 11.0 in the absence of salt and at pH 3.0–9.0 in the presence of different concentrations of NaCl and KCl. The specific growth rate of D. nepalensis was not affected by the initial pH of the medium in the absence of salts, whereas it was affected in the presence of salts. At 2 M NaCl and KCl, the organism exhibited a synergistic effect on pH and salt stress, which was unique in the Debaryomyces species. Irrespective of the initial pH and salt, the intracellular pH of D. nepalensis was ~7.0. Significant organic acid was produced at neutral and alkaline pH and organic acid production increased with the increase in pH and salt. Very specific organic acids are produced in the presence of NaCl and KCl. Our observation would contribute to a better understanding of the physiological phenomenon of halotolerance in D. nepalensis.

Bacterial extracellular polysaccharides involved in biofilm formation.

Abstract: Extracellular polymeric substances (EPS) produced by microorganisms are a complex mixture of biopolymers primarily consisting of polysaccharides, as well as proteins, nucleic acids, lipids and humic substances. EPS make up the intercellular space of microbial aggregates and form the structure and architecture of the biofilm matrix. The key functions of EPS comprise the mediation of the initial attachment of cells to different substrata and protection against environmental stress and dehydration. The aim of this review is to present a summary of the current status of the research into the role of EPS in bacterial attachment followed by biofilm formation. The latter has a profound impact on an array of biomedical, biotechnology and industrial fields including pharmaceutical and surgical applications, food engineering, bioremediation and biohydrometallurgy. The diverse structural variations of EPS produced by bacteria of different taxonomic lineages, together with examples of biotechnological applications, are discussed. Finally, a range of novel techniques that can be used in studies involving biofilm-specific polysaccharides is discussed.

The distribution and function of phosphatidylserine in cellular membranes.

Abstract: Phosphatidylserine (PS) is the most abundant negatively charged phospholipid in eukaryotic membranes. PS directs the binding of proteins that bear C2 or gamma-carboxyglutamic domains and contributes to the electrostatic association of polycationic ligands with cellular membranes. Rather than being evenly distributed, PS is found preferentially in the inner leaflet of the plasma membrane and in endocytic membranes. The loss of PS asymmetry is an early indicator of apoptosis and serves as a signal to initiate blood clotting. This review discusses the determinants and functional implications of the subcellular distribution and membrane topology of PS.