Mycobacterial Stress Regulation: The Dps ``Twin Sister'' Defense Mechanism and Structure-Function Relationship

In this work, we have tried to emphasize the connection between mycobacterial growth and regulation of gene expression. Utilization of multiple carbon sources and diauxic growth helps bacteria to regulate gene expression at an optimum level so that the inhospitable conditions encountered during nutrient depletion can be circumvented. These aspects will be discussed with respect to mycobacterial growth in subsequent sections. Identification and characterization of genes induced under such conditions is helpful to understand the physiology of the bacterium. Although it is necessary to compare the total expression profile of proteins as they transit from vegetative growth to stationary phase, at times a lot of insights can be deciphered from the expression pattern of one or two proteins. We have compared the protein expression and sigma factor selectivity of two such proteins in M. smegmatis to understand the differential regulation of genes playing diverse function in the same species. Some newer insights on the structure and function of one of the Dps proteins are also explained.

Diverse functions of restriction-modification systems in addition to cellular defense

Restriction-modification (R-M) systems are ubiquitous and are often considered primitive immune systems in bacteria. Their diversity and prevalence across the prokaryotic kingdom are an indication of their success as a defense mechanism against invading genomes. However, their cellular defense function does not adequately explain the basis for their immaculate specificity in sequence recognition and nonuniform distribution, ranging from none to too many, in diverse species. The present review deals with new developments which provide insights into the roles of these enzymes in other aspects of cellular function. In this review, emphasis is placed on novel hypotheses and various findings that have not yet been dealt with in a critical review. Emerging studies indicate their role in various cellular processes other than host defense, virulence, and even controlling the rate of evolution of the organism. We also discuss how R-M systems could have successfully evolved and be involved in additional cellular portfolios, thereby increasing the relative fitness of their hosts in the population.

NSs Encoded by Groundnut Bud Necrosis Virus Is a ifunctional Enzyme

Groundnut bud necrosis virus (GBNV), a member of genus Tospovirus in the family Bunyaviridae, infects a large number of leguminosae and solanaceae plants in India. With a view to elucidate the function of nonstructural protein, NSs encoded by the small RNA genome (S RNA), the NSs protein of GBNV-tomato (Karnataka) [1] was over-expressed in E.coli and purified by Ni-NTA chromatography. The purified rNSs protein exhibited an RNA stimulated NTPase activity. Further, this activity was metal ion dependent and was inhibited by adenosine 5' (beta, gamma imido) triphosphate, an ATP analog. The rNSs could also hydrolyze dATP.Interestingly, in addition to the NTPase and dATPase activities, the rNSs exhibited ATP independent 5' RNA/DNA phosphatase activity that was completely inhibited by AMP. The 5' alpha phosphate could be removed from ssDNA, ssRNA, dsDNA and dsRNA thus confirming that rNSs has a novel 5' alpha phosphatase activity. K189A mutation in the Walker motif A (GxxxxGKT) resulted in complete loss of ATPase activity, but the 5'phosphatase activity was unaffected. On the other hand, D159A mutation in the Walker motif B (DExx) resulted in partial loss of both the activities. These results demonstrate for the first time that NSs is a bifunctional enzyme, which could participate in viral movement, replication or in suppression of the host defense mechanism.

Visiting the cell biology of Salmonella infection

Salmonella, a Gram-negative facultative intracellular pathogen is capable of infecting vast array of hosts. The striking ability of Salmonella to overcome every hurdle encountered in the host proves that they are true survivors. In the host, Salmonella infects various cell types and needs to survive and replicate by countering the defense mechanism of the specific cell. In this review, we will summarize the recent insights into the cell biology of Salmonella infection. Here, we will focus on the findings that deal with the specific mechanism of various cell types to control Salmonella infection. Further, the survival strategies of the pathogen in response to the host immunity will also be discussed in detail. Better understanding of the mechanisms by which Salmonella evade the host defense system and establish pathogenesis will be critical in disease management. (C) 2010 Institut Pasteur. Published by Elsevier Masson SAS. All rights reserved.

A New Mechanism For Ferromagnetism In C-60-TDAE

Based on the topology of C-60 and the resulting non-disjoint nature of the lowest unoccupied molecular orbitals, Ne propose a new model for ferromagnetic exchange in C-60-TDAE. Within the Hubbard model, we find that the ferromagnetic exchange integral is stabilized to first order in the inter-ball transfer integral, while the antiferromagnetic coupling is stabilized only to second order. This difference is adequate to counter the larger phase space available for stabilizing the antiferromagnetic state. Thus, the ground state is found to be ferromagnetic for reasonable inter-ball transfer integrals.

Mechanism of foetal wastage following immunoneutralization of riboflavin carrier protein in the pregnant rat: disturbances in flavin coenzyme levels

Immunoneutralization of maternal RCP results in a >90% decrease in the content and the incorporation of [2-14C]riboflavin into embryonic FAD as well as a percentage redistribution of both embryonic FMN and riboflavin. This is unaccompanied by any discernible changes in flavin distribution pattern in the maternal liver. Embryonic α-glycerophosphate dehydrogenase and NADPH-cytochrome c reductase register significant decreases in activities in the RCP antiserum-treated rats. These alterations readily explain the arrest of foetal growth culminating in pregnancy termination in the antiserum-treated animals.

Mechanism of coupling periodate-oxidized nucleosides to proteins

This paper describes a mechanism of coupling periodate-oxidized nucleosides to proteins. Each of the dialdehyde groups of a periodate-oxidized nucleoside is shown to couple to lysine residues on different protein molecules through Schiff bases, thereby cross-linking different protein molecules, forming a polymer. This is in contrast to the previous model in which nucleosides were suggested to couple to proteins through a morpholine structure. The cross-linked structure of the nucleoside-antigen, significantly different when compared to the native protein, may affect the specificity and the efficiency of antibody production.

Spool valve mechanism used in a 20 K Gifford-McMahon cycle cryorefrigerator and its effect on the P-V diagram

The design and fabrication of a spool valve for a two-stage Gifford-McMahon cycle cryorefrigerator is described. The effect of this valve on the P-V diagram and practical methods of reducing the P-V degradation are also discussed.

Catalysis and mechanism of malonyl transferase activity in type II fatty acid biosynthesis acyl carrier proteins

One of the unexplored, yet important aspects of the biology of acyl carrier proteins (ACPs) is the self-acylation and malonyl transferase activities dedicated to ACPs in polyketide synthesis. Our studies demonstrate the existence of malonyl transferase activity in ACPs involved in type II fatty acid biosynthesis from Plasmodium falciparum and Escherichia coli. We also show that the catalytic malonyl transferase activity is intrinsic to an individual ACP. Mutational analysis implicates an arginine/lysine in loop II and an arginine/glutamine in helix III as the catalytic residues for transferase function. The hydrogen bonding properties of these residues appears to be indispensable for the transferase reaction. Complementation of fabD(Ts) E. coli highlights the putative physiological role of this process. Our studies thus shed light on a key aspect of ACP biology and provide insights into the mechanism involved therein.

Mechanism of high-temperature superconductivity in YBa2Cu3O7−δ: Crucial role of oxygen

Oxygen atoms in the middle Cu---O layer of YBa2Cu3O7 consisting of strings of corner-connected (CuO4)∞ units are shown to be crucial for superconductivity. Importance of hole-hole pairing giving rise to O---O bonds is also indicated.

Metal Chelates in Vinyl Polymerization: Kinetics and Mechanism of Acrylonitrile Polymerization Initiated by Cu(I1) Imine Complexes

The free radical polymerization of acrylonitrile (AN) initiated by Cu(I1) 4-anilino 3-pentene 2-one [Cu(II) ANIPO] Cu(II), 4-p-toluedeno 3-pentene 2-one [Cu(II) TPO], and Cu(I1) 4-p-nitroanilino 3-pentene 2-one [Cu(II) NAPO] was studied in benzene at 50 and 60°C and in carbon tetrachloride (CCld), dimethyl sulfoxide (DMSO), and methanol (MeOH) at 60°C. Although the polymerization proceeded in a heterogeneous phase, it followed the kinetics of a homogeneous process. The monomer exponents were 22 at two different temperatures and in different solvents. The square-root dependence of R, on initiator concentration and higher monomer exponents accounted for a 1:2 complex formation between the chelate and monomer. The complex formatign was shown by ultraviolet (UV) study. The activation energies, kinetics, and chain transfer constants were also evaluated.

Mechanism of oxidation of α,β-unsaturated thiones by singlet oxygen

Photo-oxidation of α,β-unsaturated thiones yields the corresponding ketones as the only product. Studies carried out on three systems, namely thioketones, α,β-unsaturated thiones and thioketenes, have revealed that there exists a similarity in their mechanism of oxidation. It has been suggested that the thiocarbonyl chromophore is the site of attack by singlet oxygen in α,β-unsaturated thiones and that the adjacent C-C double bond is inert under these conditions. Absence of sulphine during the oxidation of α,β-unsaturated thiones is attributed to the electronic factors operating on the zwitterionic/diradical intermediate. While α,β-unsaturated ketones are poorly reactive, α,β-unsaturated thiones are highly reactive toward singlet oxygen.

Mechanism of catalytic activity of metal oxides and chromites on ammonium perchlorate pyrolysis

This study investigates the mechanism of action of transition metal chromites on the decomposition of ammonium perchlorate.

Structures of mannose-6-phosphate isomerase from Salmonella typhimurium bound to metal atoms and substrate: implications for catalytic mechanism

Mannose-6-phosphate isomerase (MPI) catalyzes the inter-conversion of mannose 6-phosphate and fructose 6-phosphate. X-ray crystal structures of MPI from Salmonella typhimurium in the apo form (with no metal bound) and in the holo form (with bound Zn2+) and two other structures with yttrium bound at an inhibitory site and complexed with Zn2+ and fructose 6-phosphate (F6P) were determined in order to gain insights into the structure and the isomerization mechanism. Isomerization involves acid/base catalysis with proton transfer between the C1 and C2 atoms of the substrate. His99, Lys132, His131 and Asp270 are close to the substrate and are likely to be the residues involved in proton transfer. The interactions observed at the active site suggest that the ring-opening step is probably catalyzed by His99 and Asp270. An active-site loop consisting of residues 130-133 undergoes conformational changes upon substrate binding. Zn2+ binding induces structural order in the loop consisting of residues 50-54. The metal atom appears to play a role in substrate binding and is probably also important for maintaining the architecture of the active site. Isomerization probably follows the previously suggested cis-enediol mechanism.