Pressure effect on the stability and the conformational dynamics of the D-Galactose/D-Glucose-binding protein from Escherichia coli

The effect of the pressure on the structure and stability of the D-Galactose/D-Glucose binding protein (GGBP) from Escherichia coli was studied by steady-state and time-resolved fluorescence spectroscopy, and the ability of glucose ligand to stabilize the GGBP structure was also investigated. Steady-state fluorescence experiments showed a marked quenching of fluorescence emission of GGBP in the absence of glucose. Instead, the presence of glucose seems to stabilize the structure of GGBP at low and moderate pressure values. Time-resolved fluorescence measurements showed that the GGBP taumean in the absence of glucose varies significantly up to 600 bar, while in the presence of the ligand it is almost unaffected by pressure increase up to 600 bar. The effect of the pressure on GGBP was also studied by molecular dynamics simulations. The simulation data support the spectroscopic results and confirm that the presence of glucose is able to contrast the negative effects of pressure on the protein structure. Taken together, the spectroscopic and computer simulation studies suggest that at pressure values up to 2000 bar the structure of GGBP in the absence of glucose remains folded, but a significant perturbation of the protein secondary structures can be detected. The binding of glucose reduces the negative effect of pressure on protein structure and confers protection from perturbation especially at moderate pressure values.     

Structural and magnetic characteristics of tetramethylammonium tetrahalogenoferrates(III)

A series of tetramethylammonium tetrahalogenoferrates(III), [FeBr_4−nCl_n]⁻ (n = 0, 1, 3, 4), of general formula [(CH₃)₄N][FeBr_4−nCl_n], have been synthesized. The crystal and molecular structures of [(CH₃)₄N][FeCl₄] were determined. The compound is isostructural with its [FeBr_4−nCl_n]⁻ (n = 0, 1, 3, 4) analogues. Magnetic measurements of the powdered samples of [(CH₃)₄N][FeBr_4−nCl_n] gave negative values of the Weiss constant, which suggest antiferromagnetic coupling. The strength of the antiferromagnetic interactions strongly depends on the kind of halide ligands in the coordination sphere of iron(III) and increases with an increasing number of the bromide anions.     

A conformational change in the eukaryotic translation preinitiation complex and release of eIF1 signal recognition of the start codon

During eukaryotic translation initiation, ribosomal 43S complexes scan mRNAs for the correct AUG codon at which to begin translation. Start codon recognition triggers GTP hydrolysis, committing the complex to engagement at that point on the mRNA. While fidelity at this step is essential, the nature of the codon recognition event and the mechanism by which it activates GTP hydrolysis are poorly understood. Here we report the changes that occur within the 43S.mRNA complex in response to AUG codon recognition. eIF1 and eIF1A are key players in assembly of 43S.mRNA complexes capable of locating initiation codons. We observed FRET between these two factors when bound to the 40S subunit. Using steady-state FRET, anisotropy, and kinetic analyses, we demonstrate that start codon recognition results in a conformational change and release of eIF1 from the ribosome. These rearrangements probably play a role in triggering GTP hydrolysis and committing the complex to downstream events.     

Novel gene and gene model detection using a whole genome open reading frame analysis in proteomics

Background  

Defining the location of genes and the precise nature of gene products remains a fundamental challenge in genome annotation. Interrogating tandem mass spectrometry data using genomic sequence provides an unbiased method to identify novel translation products. A six-frame translation of the entire human genome was used as the query database to search for novel blood proteins in the data from the Human Proteome Organization Plasma Proteome Project. Because this target database is orders of magnitude larger than the databases traditionally employed in tandem mass spectra analysis, careful attention to significance testing is required. Confidence of identification is assessed using our previously described Poisson statistic, which estimates the significance of multi-peptide identifications incorporating the length of the matching sequence, number of spectra searched and size of the target sequence database.     

Human adrenoleukodystrophy protein and related peroxisomal ABC transporters interact with the peroxisomal assembly protein PEX19p

Four ABC half transporters (ALDP, ALDRP, PMP70, and PMP69) have been identified in the mammalian peroxisomal membrane but no function has been unambiguously assigned to any of them. To date X-linked adrenoleukodystrophy (X-ALD) is the only human disease known to result from a defect of one of these ABC transporters, ALDP. Using the yeast two-hybrid system and in vitro GST pull-down assays, we identified the peroxin PEX19p as a novel interactor of ALDP, ALDRP, and PMP70. The cytosolic farnesylated protein PEX19p was previously shown to be involved in an early step of the peroxisomal biogenesis. The PEX19p interaction occurs in an internal N-terminal region of ALDP which we verified to be important for proper peroxisomal targeting of this protein. Farnesylated wild-type PEX19p and a farnesylation-deficient mutant PEX19p did not differ in their ability to bind to ALDP. Our data provide evidence that PEX19p is a cytosolic acceptor protein for the peroxisomal ABC transporters ALDP, PMP70, and ALDRP and might be involved in the intracellular sorting and trafficking of these proteins to the peroxisomal membrane.     

Kinetic model of oxidation catalyzed by xanthine oxidase-the final enzyme in degradation of purine nucleosides and nucleotides

A new kinetic model is presented for analysis of experimental data of oxidation process catalyzed by milk xanthine oxidase. The kinetics for two substrates, xanthine and its analog 2-chloroadenine, in a broad pH range (5.8-9.0) are best described by an equation which is a rational function of degree 2:3 and 2:2, respectively.     

Quantitative trait loci for plant height in Maresi × CamB barley population and their associations with yield-related traits under different water regimes

High-yielding capacity of the modern barley varieties is mostly dependent on the sources of semi-dwarfness associated with the sdw1/denso locus. The objective of the study was to identify quantitative trait loci (QTLs) associated with the plant height and yield potential of barley recombinant inbred lines (RILs) grown under various soil moisture regimes. The plant material was developed from a hybrid between the Maresi (European cv.) and CamB (Syrian cv.). A total of 103 QTLs affecting analysed traits were detected and 36 of them showed stable effects over environments. In total, ten QTLs were found to be significant only under water shortage conditions. Nine QTLs affecting the length of main stem were detected on 2H-6H chromosomes. In four of the detected QTLs, alleles contributed by Maresi had negative effects on that trait, the most significant being the QLSt-3H.1-1 in the 3H.1 linkage group. The close linkage between QTLs identified around the sdw1/denso locus, with positive alleles contributed by Maresi, indicates that the semi-dwarf cv. Maresi could serve as a donor of favourable traits resulting in grain yield improvement, also under water scarcity. Molecular analyses revealed that the Syrian cv. also contributed alleles which increased the yield potential. Available barley resources of genomic annotations were employed to the biological interpretation of detected QTLs. This approach revealed 26 over-represented Gene Ontology terms. In the projected support intervals of QGWS_l-5H.3-2 and QLSt-5H.3 on the chromosome 5H, four genes annotated to ‘response to stress’ were found. It suggests that these QTL-regions may be involved in a response of plant to a wide range of environmental disturbances.     

Ultrabright fluorescein-labeled antibodies near silver metallic surfaces

Fluorescein-labeled antibodies are widely used in clinical assays and fluorescence microscopy. The fluorescent signal per labeled antibody is limited by fluorescein self-quenching, which occurs when the antibody is heavily labeled with multiple fluoresceins. We examined immunoglobulin G (IgG) when labeled with 0.7 to about 30 fluoresceins per antibody molecule. The extent of self-quenching was decreased, and the signal increased, when the labeled antibody was in close proximity to metallic silver particles. Time-resolved measurements showed that the intensity increase was due in part to a silver-induced increase in the radiative decay rate. These results suggest the use of labeled antibodies conjugated to silver particles as ultrabright probes for imaging or analytical applications.     

Fluorescence quenching and kinetic studies of conformational changes induced by DNA and cAMP binding to cAMP receptor protein from Escherichia coli

Cyclic AMP receptor protein (CRP) regulates the expression of more then 100 genes in Escherichia coli. It is known that the allosteric activation of CRP by cAMP involves a long-distance signal transmission from the N-terminal cAMP-binding domain to the C-terminal domain of CRP responsible for the interactions with specific sequences of DNA. In this report we have used a CRP mutant containing a single Trp13 located in the N-terminal domain of the protein. We applied the iodide and acrylamide fluorescence quenching method in order to study how different DNA sequences and cAMP binding induce the conformational changes in the CRP molecule. The results presented provide evidence for the occurrence of a long-distance conformational signal transduction within the protein from the C-terminal DNA-binding domain to the N-terminal domain of CRP. This conformational signal transmission depends on the promoter sequence. We also used the stopped-flow and Forster resonance energy transfer between labeled Cys178 of CRP and fluorescently labeled DNA sequences to study the kinetics of DNA-CRP interactions. The results thus obtained lead to the conclusion that CRP can exist in several conformational states and that their distribution is affected by binding of both the cAMP and of specific DNA sequences.