Sathyanarayana N. Gummadi

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

Purification and biochemical properties of microbial pectinases—a review

Abstract: Pectinases are a complex group of enzymes that degrade various pectic substances present in plant tissues. Pectinases have potential applications in fruit, paper and textile industries. Apart from these industrial applications, these enzymes possess biological importance in protoplast fusion technology and plant pathology. Since applications of pectinases in various fields are widening, it is important to understand the nature and properties of these enzymes for efficient and effective usage. For the past few years, vigorous research has been carried out on isolation and characterization of pectinases. New affinity matrices with improved characteristics and affinity-precipitation techniques have been developed for purification of pectinases. Recently much attention has been focused on chemical modification of pectinases and their catalytic performance by various researchers. These studies are helpful in determining key amino acid residues responsible for substrate binding, catalytic action, and physico-chemical environmental conditions for maximum hydrolysis. This short review highlights progress on purification and understanding the biochemical aspects of microbial pectinases.

Phospholipid scramblases: an overview.

Abstract: Phospholipid scramblases are a group of homologous proteins that are conserved in all eukaryotic organisms. They are believed to be involved in destroying plasma membrane phospholipid asymmetry at critical cellular events like cell activation, injury and apoptosis. However, a detailed mechanism of phospholipid scrambling still awaits a proper understanding. The most studied member of this family, phospholipid scramblase 1 (PLSCR1) (a 37 kDa protein), is involved in rapid Ca 2+ dependent transbilayer redistribution of plasma membrane phospholipids. Recently the function of PLSCR1 as a phospholipids translocator has been challenged and evidences suggest that PLSCR1 acts as signaling molecule. It has been shown to be involved in protein phosphorylation and as a potential activator of genes in response to interferon and other cytokines. Interferon induced rapid biosynthesis of PLSCR1 targets some of the protein into the nucleus, where it binds to the promoter region of inositol 1,4,5-triphosphate (IP3) receptor type 1 (IP3R1) gene and induces its expression. Palmitoylation of PLSCR1 acts as a switch, controlling its localization either to the PM or inside the nucleus. In the present review, we discuss the current understanding of PLSCR1 in relation to its trafficking, localization and signaling functions.

Microbial and enzymatic methods for the removal of caffeine

Abstract: Caffeine is a purine alkaloid and is a major constituent of coffee, tea and other beverages. It acts as a central nervous system stimulant and also has negative withdrawal effects. Decaffeinated beverages are being used to overcome its negative effects. Decaffeination is done by different methods like solvent, water and super critical fluid extraction. These methods apart from being non-specific are expensive and involve the usage of toxic organic solvents. Development of a process involving an enzymatic (specific) degradation of caffeine to non-toxic compound is necessary to solve the problems of chemical extraction of caffeine in food products as well as treating the caffeine containing waste products. The different microbial and enzymatic methods of caffeine removal are discussed in this review. The literature revealed that major caffeine degrading strains belong to Pseudomonas and Aspergillus. Though the enzymes involved in degradation of caffeine by microorganisms are known, in vitro enzymatic studies for caffeine degradation is not yet reported.

Catabolic pathways and biotechnological applications of microbial caffeine degradation

Abstract: Catabolism of caffeine (1,3,7-trimethylxanthine) in microorganisms commences via two possible mechanisms: demethylation and oxidation. Through the demethylation route, the major metabolite formed in fungi is theophylline (1,3-dimethylxanthine), whereas theobromine (3,7-dimethylxanthine) is the major metabolite in bacteria. In certain bacterial species, caffeine has also been oxidized directly to trimethyl uric acid in a single step. The conversion of caffeine to its metabolites is primarily brought about by N-demethylases (such as caffeine demethylase, theobromine demethylase and heteroxanthinedemethylase), caffeine oxidase and xanthine oxidase that are produced by several caffeine-degrading bacterial species such as Pseudomonas putida and species within the genera Alcaligenes, Rhodococcus and Klebsiella. Development of biodecaffeination techniques using these enzymes or using whole cells offers an attractive alternative to the present existing chemical and physical methods removal of caffeine, which are costly, toxic and non-specific to caffeine. This review mainly focuses on the biochemistry of microbial caffeine degradation, presenting recent advances and the potential biotechnological application of caffeine-degrading enzymes.

Chemical Modification Identifies Two Populations of Glycerophospholipid Flippase in Rat Liver ER

Abstract: Transbilayer flipping of glycerophospholipids in the endoplasmic reticulum (ER) is a key feature of membrane biogenesis. Flipping appears to be an ATP-independent, bidirectional process facilitated by specific proteins or flippases. Although a phospholipid flippase has yet to be identified, evidence supporting the existence of dedicated flippases was recently obtained through biochemical reconstitution studies showing that certain chromatographically resolved fractions of detergent-solubilized ER proteins were enriched in flippase activity, whereas others were inactive. We now extend these studies by describing two convenient assays of flippase activity utilizing fluorescent phospholipid analogues as transport reporters. We use these assays to show that (i) proteoliposomes generated from a flippase-enriched Triton X-100 extract of ER can flip analogues of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine; (ii) flipping of all three phospholipids is likely due to the same flippase(s) rather than distinct, phospholipid-specific transport proteins; (iii) functional flippases represent approximately 1% (w/w) of ER membrane proteins in the Triton extract; and (iv) glycerophospholipid flippase activity in the ER can be attributed to two functionally distinct proteins (or classes of proteins) defined by their sensitivity to the cysteine and histidine modification reagents N-ethylmaleimide and diethylpyrocarbonate, respectively. Analyses of the N-ethylmaleimide-sensitive class of flippase activity revealed that the functionally critical sulfhydryl group in the flippase protein is buried in a hydrophobic environment in the membrane but becomes reactive on extraction of the protein into Triton X-100. This observation holds considerable promise for future attempts to isolate the flippase via an affinity approach.

Microbial pectinolytic enzymes: A review

Abstract: Pectinases or petinolytic enzymes, hydrolyze pectic substances. They have a share of 25% in the global sales of food enzymes. Pectinases are one of the most widely distributed enzymes in bacteria, fungi and plants. Protopectinases, polygalacturonases, lyases and pectin esterases are among the extensively studied pectinolytic enzymes. Protopectinases catalyze the solubilization of protopectin. Polygalacturonases hydrolyze the polygalacturonic acid chain by addition of water and are the most abundant among all the pectinolytic enzymes. Lyases catalyze the trans-eliminative cleavage of the galacturonic acid polymer. Pectinesterases liberate pectins and methanol by de-esterifying the methyl ester linkages of the pectin backbone. Pectinolytic enzymes are of significant importance in the current biotechnological era with their all-embracing applications in fruit juice extraction and its clarification, scouring of cotton, degumming of plant fibers, waste water treatment, vegetable oil extraction, tea and coffee fermentations, bleaching of paper, in poultry feed additives and in the alcoholic beverages and food industries. The present review mainly contemplates on the types and structure of pectic substances, the classification of pectinolytic enzymes, their assay methods, physicochemical and biological properties and a bird's eye view of their industrial applications.

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.

Neuronal calcium mishandling and the pathogenesis of Alzheimer's disease.

Abstract: Perturbed neuronal Ca 2+ homeostasis is implicated in age-related cognitive impairment and Alzheimer's disease (AD). With advancing age, neurons encounter increased oxidative stress and impaired energy metabolism, which compromise the function of proteins that control membrane excitability and subcellular Ca 2+ dynamics. Toxic forms of amyloid β-peptide (Aβ) can induce Ca 2+ influx into neurons by inducing membrane-associated oxidative stress or by forming an oligomeric pore in the membrane, thereby rendering neurons vulnerable to excitotoxicity and apoptosis. AD-causing mutations in the β-amyloid precursor protein and presenilins can compromise these normal proteins in the plasma membrane and endoplasmic reticulum, respectively. Emerging knowledge of the actions of Ca 2+ upstream and downstream of Aβ provides opportunities to develop novel preventative and therapeutic interventions for AD.

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.

Autoimmunity and the Clearance of Dead Cells

Abstract: To maintain organismal homeostasis, phagocytes engulf dead cells, which are recognized as dead by virtue of a characteristic "eat me" signal exposed on their surface. The dead cells are then transferred to lysosomes, where their cellular components are degraded for reuse. Inefficient engulfment of dead cells activates the immune system, causing disease such as systemic lupus erythematosus, and if the DNA of the dead cells is not properly degraded, the innate immune response becomes activated, leading to severe anemia and chronic arthritis. Here, we discuss how the endogenous components of dead cells activate the immune system through both extracellular and intracellular pathways.