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1.
In order to understand the thermodynamic and kinetic basis of the intrinsic stability of proteins from hyperthermophiles, the folding-unfolding reactions of cysteine-free pyrrolidone carboxyl peptidase (Cys142/188Ser) (PCP-0SH) from Pyrococcus furiosus were examined using circular dichroism (CD) and differential scanning calorimetry (DSC) at pH 2.3, where PCP-0SH exists in monomeric form. DSC showed a strong dependence of the shape and position of the unfolding profiles on the scan rate, suggesting the stability of PCP-0SH under kinetic control. On DSC timescales, even at a scan rate of 1 deg. C/hour, heat denaturation of PCP-0SH was non-equilibrium. However, over a long period of incubation of the heat-denatured PCP-0SH at pre-transition temperatures, it refolded completely, indicating reversibility with very slow relaxation kinetics. The rates of refolding of the heat-denatured PCP-0SH determined from the time-resolved DSC and CD spectroscopic progress curves were found to be similar within experimental error, confirming the mechanism of refolding to be a two-state process. The equilibrium established with a relaxation time of 5080 seconds (at t(m)=46.5 degrees C), which is unusually higher than the relaxation times observed for mesophilic and hyperthermophilic proteins. The long relaxation time may lead to the apparent irreversibility of an unfolding process occurring on the DSC experiment timescale. The refolding rate (9.8 x 10(-5) s(-1)) peaked near the t(m) (=46.5 degrees C), whereas the stability profile reached maxima (11.8 kJ mol(-1)) at 17 degrees C. The results clearly indicate the unusual mode of protein destabilization via a drastic decrease in the rate of folding at low pH and still maintaining a high activation energy barrier (284 kJ mol(-1)) for unfolding, which provides an effective kinetic advantage to unusually stable proteins from hyperthermophiles.  相似文献   
2.
This structure-activity relationship study for neonicotinoids with an N-haloacetylimino pharmacophore identifies several candidate compounds showing outstanding insecticidal potency and consequently leads to establishing their molecular recognition at an insect nicotinic receptor structural model, wherein the neonicotinoid halogen atoms (fluorine, chlorine, bromine, and iodine) variously interact with the receptor loops C-D interfacial niche via H-bonding and/or hydrophobic interactions.  相似文献   
3.
Capnocytophaga ochracea is present in the dental plaque biofilm of patients with periodontitis. Biofilm cells change their phenotype through quorum sensing in response to fluctuations in cell-population density. Quorum sensing is mediated by auto-inducers (AIs). AI-2 is involved in intercellular signaling, and production of its distant precursor is catalyzed by LuxS, an enzyme involved in the activated methyl cycle. Our aim was to clarify the role of LuxS in biofilm formation by C. ochracea. Two luxS-deficient mutants, TmAI2 and LKT7, were constructed from C. ochracea ATCC 27872 by homologous recombination. The mutants produced significantly less AI-2 than the wild type. The growth rates of these mutants were similar to that of the wild-type in both undiluted Tryptic soy broth and 0.5 × Tryptic soy broth. However, according to crystal violet staining, they produced significantly less biofilm than the wild type. Confocal laser scanning microscopy and scanning electron microscopy showed that the biofilm of the TmAI2 strain had a rougher structure than that of the wild type. Complementation of TmAI-2 with extrinsic AI-2 from the culture supernatant of wild-type strain did not restore biofilm formation by the TmAI2 strain, but complementation of LKT7 strain with luxS partially restored biofilm formation. These results indicate that LuxS is involved in biofilm formation by C. ochracea, and that the attenuation of biofilm formation by the mutants is likely caused by a defect in the activated methyl cycle rather than by a loss of AI-2.  相似文献   
4.
Two novel tachykinins (OctTK-I: Lys-Pro-Pro-Ser-Ser-Ser-Glu-Phe-Ile-Gly-Leu-Met-NH(2) and OctTK-II: Lys-Pro-Pro-Ser-Ser-Ser-Glu-Phe-Val-Gly-Leu-Met-NH(2)) were isolated from the posterior salivary gland of the octopus (Octopus vulgaris) using a contraction assay of the carp rectum. These peptides had in common the pentapeptide sequence -Phe-X-Gly-Leu-Met-NH(2) at the C-terminal and induced immediate contractions on the carp rectum and the guinea-pig ileum. cDNAs encoding their precursor proteins were cloned. The OctTK gene was expressed in the posterior salivary gland and the expression was localized in mucus-secreting cells of the gland. The results suggested that OctTKs might be secreted as a venomous substance acting on vertebrates such as fishes, which are the prey or natural enemies of the octopus.  相似文献   
5.
Recently, we discovered novel silver(I)-mediated cytosine–cytosine base pair (C–AgI–C) in DNA duplexes. To understand the properties of these base pairs, we searched for a DNA sequence that can be used in NMR structure determination. After extensive sequence optimizations, a non-symmetric 15-base-paired DNA duplex with a single C–AgI–C base pair flanked by 14 A–T base pairs was selected. In spite of its challenging length for NMR measurements (30 independent residues) with small sequence variation, we could assign most non-exchangeable protons (254 out of 270) and imino protons for structure determination.  相似文献   
6.
An alpha-C-iodoethynylglucose derivative was coupled with an L-serine-derived zinc-copper reagent to give alpha-C-glucosylpropargyl glycine, which underwent palladium catalyzed-heteroannulation with o-iodoaniline to give not alpha-C-glucosyl-tryptophan but alpha-C-glucosyl-iso-tryptophan. This is the first observation of complete reverse regioselectivity to Larock's proposal.  相似文献   
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For injectable-sized liposome complexed with DNA (lipoplexes) with high transfection efficiency of genes, we initially prepared small-sized liposomes by addition of biosurfactant. For selectivity of gene expression, the thymidine kinase (MK-tk) gene controlled by midkine was used for herpes simplex virus thymidine kinase (HSV-tk) gene therapy. Liposomes composed of 3([N-(N′,N′–dimethylaminoethane)-carbamoyl] cholesterol (DC-Chol), L-dioleoylphosphatidylethanolamine (DOPE), and a biosurfactant, such as β-sitosterol β-D-glucoside (Sit-G) for Sit-G-liposomes and mannosylerythrytol lipid A (MEL) for MEL-liposomes, produced about 300-nm-sized lipoplexes. Sit-G- and MEL-liposomes showed higher transfection efficiency of the luciferase marker gene and thymidine kinase activity in the presence of serum in the cells. The treatment with transfection of MK-tk gene by Sit-G-liposome and injection of ganciclovir significantly reduced tumor growth in a solid tumor model, compared with that by Sit-G-liposome alone. This finding suggested that Sit-G-liposome is a potential vector for HSV-tk gene therapy.  相似文献   
10.
Description of Pestalotiopsis pallidotheae: a new species from Japan   总被引:1,自引:0,他引:1  
A new coelomycetes fungal species, Pestalotiopsis pallidotheae, is described. This endophytic fungus, isolated from a leaf of Japanese andromeda (Pieris japonica), has knob-tipped appendages on the apical and basal cells of the conidia. The conidial morphology is similar to that of Pestalotiopsis theae except that the color of the median cells is paler in P. pallidotheae. Molecular analyses of the ITS1-5.8S rRNA-ITS2 site placed P. pallidotheae in a group different from P. theae.  相似文献   
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