Structure of the reovirus membrane-penetration protein, Mu1, in a complex with is protector protein, Sigma3

Cell entry by nonenveloped animal viruses requires membrane penetration without membrane fusion. The reovirus penetration agent is the outer-capsid protein, Mu1. The structure of Mu1, complexed with its "protector" protein, Sigma3, and the fit of this Mu1(3)Sigma3(3) heterohexameric complex into the cryoEM image of an intact virion, reveal molecular events essential for viral penetration. Autolytic cleavage divides Mu1 into myristoylated Mu1N and Mu1C. A long hydrophobic pocket can receive the myristoyl group. Dissociation of Mu1N, linked to a major conformational change of the entire Mu1 trimer, must precede myristoyl-group insertion into the cellular membrane. A myristoyl switch, coupling exposure of the fatty acid chain, autolytic cleavage of Mu1N, and long-range molecular rearrangement of Mu1C, thus appears to be part of the penetration mechanism.     

Bioassay of three sulphur containing compounds as rat attractant admixed in cereal-based bait against Rattus rattus Linn

Three sulphur containing compounds, carbon disulphide, dimethyl disulphide and dimethyl sulphide were bioassayed for preference after admixing them in cereal base as ready bait block for use against commensal rat, R. rattus (wild type) in four way choice chamber system. Rat preference for different baits was also studied with automatic recording animal activity meter. Rats exhibited attractancy to the baits at 0.005% concentration of all the three compounds while at 0.01% concentration they have showed repellency. Dimethyl sulphide at 0.005% concentration showed better attractancy towards both sexes of rat.     

Male gametophyte development in bread wheat (Triticum aestivum L.): molecular,cellular, and biochemical analyses of a sporophytic contribution to pollen wall ontogeny

Bread wheat (hexaploid AABBDD genome; 16 billion basepairs) is a genetically complex, self-pollinating plant with bisexual flowers that produce short-lived pollen. Very little is known about the molecular biology of its gametophyte development despite a longstanding interest in hybrid seeds. We present here a comprehensive characterization of three apparently homeologous genes (TAA1a, TAA1b and TAA1c) and demonstrate their anther-specific biochemical function. These eight-exon genes, found at only one copy per haploid complement in this large genome, express specifically within the sporophytic tapetum cells. The presence of TAA1 mRNA and protein was evident only at specific stages of pollen development as the microspore wall thickened during the progression of free microspores into vacuolated-microspores. This temporal regulation matched the assembly of wall-impregnated sporopollenin, a phenylpropanoid-lipid polymer containing very long chain fatty alcohols (VLCFAlc), described in the literature. Our results establish that sporophytic genes contribute to the production of fatty alcohols: Transgenic expression of TAA1 afforded production of long/VLCFAlc in tobacco seeds (18 : 1; 20 : 1; 22 : 1; 24 : 0; 26 : 0) and in Escherichia coli (14 : 0; 16 : 0; 18 : 1), suggesting biochemical versatility of TAA1 with respect to cellular milieu and substrate spectrum. Pollen walls additionally contain fatty alcohols in the form of wax esters and other lipids, and some of these lipids are known to play a role in the highly specific sexual interactions at the pollen-pistil interface. This study provides a handle to study these and to manipulate pollen traits, and, furthermore, to understand the molecular biology of fatty alcohol metabolism in general.     

Beyond the proton abstracting role of Glu-376 in medium-chain acyl-CoA dehydrogenase: influence of Glu-376-->Gln substitution on ligand binding and catalysis

The active site residue, Glu-376, of medium-chain acyl-CoA dehydrogenase (MCAD) has been known to abstract the alpha-proton from acyl-CoA substrates during the course of the reductive half-reaction. The site-specific mutation of Glu-376-->Gln(E376Q) slows down the octanoyl-CoA-dependent reductive half-reaction of the enzyme by about 5 orders of magnitude due to impairment in the proton-transfer step. To test whether the carboxyl group of Glu-376 exclusively serves as the active site base (for abstracting the alpha-proton) during the enzyme catalysis, we undertook a detailed kinetic investigation of the enzyme-ligand interaction and enzyme catalysis, utilizing octanoyl-CoA/octenoyl-CoA as a physiological substrate/product pair and the wild-type and E376Q mutant enzymes as the catalysts. The transient kinetic data revealed that the E376Q mutation not only impaired the rate of octanoyl-CoA-dependent reduction of the enzyme-bound FAD, but also impaired the association and dissociation rates for the binding of the reaction product, octenoyl-CoA. Besides, the E376Q mutation correspondingly impaired the kinetic profiles for the quenching of the intrinsic protein fluorescence during the course of the above diverse (i.e., "chemistry" versus "physical interaction") processes. A cumulative account of the experimental data led to the suggestion that the carboxyl group of Glu-376 of MCAD is intimately involved in modulating the microscopic environment (protein conformation) of the enzyme's active site during the course of ligand binding and catalysis. Arguments are presented that the electrostatic interactions among Glu-376, FAD, and CoA-ligands are responsible for structuring the enzyme's active site cavity in the ground and transition states of the enzyme during the above physicochemical processes.     

Arabidopsis AtGPAT1, a member of the membrane-bound glycerol-3-phosphate acyltransferase gene family,is essential for tapetum differentiation and male fertility

Membrane-bound glycerol-3-phosphate acyltransferase (GPAT; EC 2.3.1.15) mediates the initial step of glycerolipid biosynthesis in the extraplastidic compartments of plant cells. Here, we report the molecular characterization of a novel GPAT gene family from Arabidopsis, designated AtGPAT. The corresponding polypeptides possess transmembrane domains and GPAT activity when expressed heterologously in a yeast lipid mutant. The functional significance of one isoform, AtGPAT1, is the focus of the present study. Disruption of the AtGPAT1 gene causes a massive pollen development arrest, and subsequent introduction of the gene into the mutant plant rescues the phenotype, illustrating a pivotal role for AtGPAT1 in pollen development. Microscopic examinations revealed that the gene lesion results in a perturbed degeneration of the tapetum, which is associated with altered endoplasmic reticulum profiles and reduced secretion. In addition to the sporophytic effect, AtGPAT1 also exerts a gametophytic effect on pollen performance, as the competitive ability of a pollen grain to pollinate is dependent on the presence of an AtGPAT1 gene. Deficiency in AtGPAT1 correlates with several fatty acid composition changes in flower tissues and seeds. Unexpectedly, however, a loss of AtGPAT1 causes no significant change in seed oil content.     

Crab shell chitin whisker reinforced natural rubber nanocomposites. 2. Mechanical behavior

In a previous work (part 1), nanocomposite materials were obtained using a latex of either unvulcanized or prevulcanized natural rubber as the matrix and a colloidal suspension of crab chitin whiskers as the reinforcing phase. The mechanical behavior of the resulting nanocomposite films was analyzed in both the linear and the nonlinear range in the present study. The effects of the filler and processing technique were evaluated, and the results are discussed based on the knowledge of the structural morphology and swelling behavior reported in our previous work. The reinforcing effect of chitin whiskers strongly depended on their ability to form a rigid three-dimensional network, resulting from strong interactions such as hydrogen bonds between the whiskers. The results emanating from the successive tensile test experiments give clear evidence for the presence of a three-dimensional chitin network within the evaporated samples. Cross-linking of the matrix was found to interfere with the formation of this network.     

Crab shell chitin whisker reinforced natural rubber nanocomposites. 1. Processing and swelling behavior

Nanocomposite materials were obtained from a colloidal suspension of chitin whiskers as the reinforcing phase and latex of both unvulcanized and prevulcanized natural rubber as the matrix. The chitin whiskers, prepared by acid hydrolysis of chitin from crab shell, consisted of slender parallelepiped rods with an aspect ratio close to 16. After the two aqueous suspensions were mixed and strirred, solid composite films were obtained either by freeze-drying and hot-pressing or by casting and evaporating the preparations. The processing and swelling behavior of composite films were evaluated. It was concluded that the whiskers form a rigid network assumed to be governed by a percolation mechanism in the evaporated samples only. Comparatively, better resistance of evaporated samples than hot-pressed ones against swelling in an organic solvent medium is good evidence for the existence of a rigid chitin network. The values of diffusion coefficient, bound rubber content, and relative weight loss also supported the presence of a three-dimensional chitin network within the evaporated samples. The mechanical behavior of the composites gives additional insight and evidence for this fact (part 2).