Epoxidation of cottonseed oil by aqueous hydrogen peroxide catalysed by liquid inorganic acids

The kinetics of epoxidation of cottonseed oil by peroxyacetic acid generated in situ from hydrogen peroxide and glacial acetic acid in the presence of liquid inorganic acid catalysts were studied. It was possible to obtain up to 78% relative conversion to oxirane with very less oxirane cleavage by in situ technique. The rate constants for sulphuric acid catalysed epoxidation of cottonseed oil were in the range 0.39-5.4 x 10(-6)L mol(-1)s(-1) and the activation energy was found to be 11.7 kcal mol(-1). Some thermodynamic parameters such as enthalpy, entropy, and free energy of activation were determined to be of 11.0 kcal mol(-1), -51.4 cal mol(-1)K(-1) and 28.1 kcal mol(-1), respectively. The order of effectiveness of catalysts was found to be sulphuric acid>phosphoric acid>nitric acid>hydrochloric acid. Acetic acid was found to be superior to formic acid for the in situ cottonseed oil epoxidation.     

Backbone and side-chain resonance assignments of <Emphasis Type="Italic">Plasmodium falciparum</Emphasis> SUMO

One of the most debilitating diseases Malaria, in its different forms, is caused by protozoan of Plasmodium species. Deadliest among these forms is the “cerebral malaria” which is afflicted upon by Plasmodium falciparum. Plasmodium adopts numerous strategies including various post-translational modifications (PTMs) to infect and survive in the human host. These PTMs have proven their critical requirement in the Plasmodium biology. Recently, sumoylation has been characterized as one of the important PTMs and many of its putative substrates have been identified in Plasmodium. Sumoylation is the covalent attachment of SUMO protein to the substrate protein, which is mediated by an enzyme cascade involving activating (E1), conjugating (E2), and ligating enzymes (E3). Here, we report resonance assignment for ¹H, ¹³C and ¹⁵N of Plasmodium falciparum SUMO (Pf-SUMO) protein determined by various 2D and 3D heteronuclear NMR experiments along with predicted secondary structures.     

Conquering the night: understanding nocturnal migration in birds

Abstract

Migration is a biologically distinct and unique phenomenon that enables the birds to migrate twice-a-year between the breeding and wintering grounds. These movements are known as spring and autumn migration, respectively. Depending on their inherent programming, the migratory birds may fly during day or night or both. Different environmental factors such as, temperature, food, predator pressure and physiological demands of energy storage and expenditure, contribute to the pattern of migrations, day or nighttime. Since, most of them are nighttime migrants they have to make dramatic changes in their physiology and behavior to transform them from being diurnal to predominantly nocturnal. These changes result in different life history stages (LHSs) such as migration, reproduction and molt, in their annual cycle, which are regulated by endogenous circadian and circannual clocks. As a result, the birds start preparing well in advance for the approaching LHS. The present review focuses on behavioral strategies of a nocturnal migrant and understanding of the possible physiological responses to ensure successful migration.     

Receptor binding,immune escape,and protein stability direct the natural selection of SARS-CoV-2 variants

Emergence of new severe acute respiratory syndrome coronavirus 2 variants has raised concerns related to the effectiveness of vaccines and antibody therapeutics developed against the unmutated wildtype virus. Here, we examined the effect of the 12 most commonly occurring mutations in the receptor-binding domain of the spike protein on its expression, stability, activity, and antibody escape potential. Stability was measured using thermal denaturation, and the activity and antibody escape potential were measured using isothermal titration calorimetry in terms of binding to the human angiotensin-converting enzyme 2 and to neutralizing human antibody CC12.1, respectively. Our results show that mutants differ in their expression levels. Of the eight best-expressed mutants, two (N501Y and K417T/E484K/N501Y) showed stronger affinity to angiotensin-converting enzyme 2 compared with the wildtype, whereas four (Y453F, S477N, T478I, and S494P) had similar affinity and two (K417N and E484K) had weaker affinity than the wildtype. Compared with the wildtype, four mutants (K417N, Y453F, N501Y, and K417T/E484K/N501Y) had weaker affinity for the CC12.1 antibody, whereas two (S477N and S494P) had similar affinity, and two (T478I and E484K) had stronger affinity than the wildtype. Mutants also differ in their thermal stability, with the two least stable mutants showing reduced expression. Taken together, these results indicate that multiple factors contribute toward the natural selection of variants, and all these factors need to be considered to understand the evolution of the virus. In addition, since not all variants can escape a given neutralizing antibody, antibodies to treat new variants can be chosen based on the specific mutations in that variant.     

Influence of cation–π interactions to the structural stability of prokaryotic and eukaryotic translation elongation factors

We have investigated the role of cation–π interactions on translation elongation factors. In our investigation, an average of four significant cation–π interactions were found, that is, an average of one cation–π interaction per 44 residues in the ten elongation factors were observed. The analysis on the influence of short (<±4), medium (>±4 to <±20) and long (>20) range contacts showed that cation–π interactions are mainly formed by medium and long-range contacts. Arg-Tyr pair was found largest in number but energetic contribution of Arg-Trp pair was found most. Preferred secondary structural conformation analysis of the residues involved in cation–π interaction indicates that the cationic Arg prefers to be in helix and Lys having equal probability for helix and strand, whereas the aromatic Phe and Trp were found mostly in helix while Tyr in strand regions. The cation–π interaction residues involved in these proteins were found highly conserved with 48.86% residues having conservation score of ≥6. Analysis of secondary structure preference of the energetically significant cation–π residues in different solvent accessible range indicates that most of the π residues are found buried or partially buried whereas cationic residues were found mostly at the protein surface. The results presented in this study will be useful for structural stability studies in translation elongation factors.     

Structural characterization of a serendipitously discovered bioactive macromolecule, lignin sulfate

The herpes simplex virus-1 (HSV-1) utilizes cell-surface glycosaminoglycan, heparan sulfate, to gain entry into cells and cause infection. In a search for synthetic mimics of heparan sulfate to prevent HSV infection, we discovered potent inhibitory activity arising from sulfation of a monomeric flavonoid. Yet, detailed screening indicated that the sulfated flavonoid was completely inactive and the potent inhibitory activity arose from a macromolecular substance present in the parent flavonoid. The active principle was identified through a battery of biophysical and chemical analyses as a sulfated form of lignin, a three-dimensional network polymer composed of substituted phenylpropanoid monomers. Mass spectral analysis of the parent lignin and its sulfated derivative indicates the presence of p-coumaryl monomers interconnected through uncondensed beta-O-4-linkages. Elemental analysis of lignin sulfate correlates primarily with a polymer of p-coumaryl alcohol containing one sulfate group. High-performance size exclusion chromatography shows a wide molecular weight distribution from 1.5 to 40 kDa suggesting significant polydispersity. Polyacrylamide gel electrophoresis (PAGE) analysis indicates a highly networked polymer that differs significantly from linear charged polymers with respect to its electrophoretic mobility. Overall, macromolecular lignin sulfate presents a multitude of substructures that can interact with biomolecules, including viral glycoproteins, using hydrophobic, hydrogen-bonding, and ionic forces. Thus, lignin sulfate represents a large number of interesting structures with potential medicinal benefits.     

A role for 3-O-sulfotransferase isoform-4 in assisting HSV-1 entry and spread

Many heparan sulfate (HS) 3-O-sulfotransferase (3-OST) isoforms generate cellular receptors for herpes simplex virus type-1 (HSV-1) glycoprotein D (gD). Interestingly, the ability of 3-OST-4 to mediate HSV-1 entry and cell-to-cell fusion has not been determined, although it is predominantly expressed in the brain, a primary target of HSV-1 infections. We report that expression of 3-OST-4 can render Chinese hamster ovary K1 (CHO-K1) cells susceptible to entry of wild-type and a mutant (Rid1) strain of HSV-1. Evidence for generation of gD receptors by 3-OST-4 was suggested by gD-mediated interference assay and the ability of 3-OST-4 expressing CHO-K1 cells to preferentially bind HSV-1 gD, which could be reversed by prior treatment of cells with HS lyases (heparinases-II/III). In addition, 3-OST-4 expressing CHO-K1 cells acquired the ability to fuse with cells-expressing HSV-1 glycoproteins. Demonstrating specificity, the cell fusion was inhibited by soluble 3-O-sulfated forms of HS, but not unmodified HS. Taken together our results suggest a role of 3-OST-4 in HSV-1 pathogenesis.     

Clustered miRNAs and their role in biological functions and diseases

MicroRNAs (miRNAs) are endogenous, small non‐coding RNAs known to regulate expression of protein‐coding genes. A large proportion of miRNAs are highly conserved, localized as clusters in the genome, transcribed together from physically adjacent miRNAs and show similar expression profiles. Since a single miRNA can target multiple genes and miRNA clusters contain multiple miRNAs, it is important to understand their regulation, effects and various biological functions. Like protein‐coding genes, miRNA clusters are also regulated by genetic and epigenetic events. These clusters can potentially regulate every aspect of cellular function including growth, proliferation, differentiation, development, metabolism, infection, immunity, cell death, organellar biogenesis, messenger signalling, DNA repair and self‐renewal, among others. Dysregulation of miRNA clusters leading to altered biological functions is key to the pathogenesis of many diseases including carcinogenesis. Here, we review recent advances in miRNA cluster research and discuss their regulation and biological functions in pathological conditions.