排序方式: 共有59条查询结果,搜索用时 15 毫秒
1.
Frans van Cauwelaert Ignace Hanssens Willy Herreman Jean-Claude van Ceunebroeck Johan Baert Hugo Berghmans 《生物化学与生物物理学报:生物膜》1983,727(2):273-284
The characteristics of small unilamellar, large unilamellar and large multilamellar vesicles of dimyristoylphosphatidylcholine and their interaction with α-lactalbumin are compared at pH 4. (1) By differential scanning calorimetry and from steady-state fluorescence anisotropy data of the lipophilic probe 1,6-diphenyl-1,3,5-hexatriene it is shown that the transition characteristics of the phospholipids in the large unilamellar vesicles resemble more those of the multilamellar vesicles than of the small unilamellar vesicles. (2) The size and composition of the lipid-protein complex formed with α-lactalbumin around the transition temperature of the lipid are independent of the vesicle type used. Fluorescence anisotropy data indicate that in this complex the motions of the lipid molecules are strongly restricted in the presence of α-lactalbumin. (3) The previous data and a comparison of the enthalpy changes, , of the interaction of the three vesicle types with α-lactalbumin allow us to derive that the enthalpy state of the small unilamellar vesicles just below 24°C is about 24 kJ/mol lipid higher than the enthalpy state of both large vesicle types at the same temperature. The abrupt transition from endothermic to exothermic values around 24°C for large vesicles approximates the transition enthalpy of the pure phospholipid 相似文献
2.
We have developed an original method for global optimization of protein side-chain conformations, called the Fast and Accurate Side-Chain Topology and Energy Refinement (FASTER) method. The method operates by systematically overcoming local minima of increasing order. Comparison of the FASTER results with those of the dead-end elimination (DEE) algorithm showed that both methods produce nearly identical results, but the FASTER algorithm is 100-1000 times faster than the DEE method and scales in a stable and favorable way as a function of protein size. We also show that low-order local minima may be almost as accurate as the global minimum when evaluated against experimentally determined structures. In addition, the new algorithm provides significant information about the conformational flexibility of individual side-chains. We observed that strictly rigid side-chains are concentrated mainly in the core of the protein, whereas highly flexible side-chains are found almost exclusively among solvent-oriented residues. 相似文献
3.
Patrick L Cable J Potts D Ignace D Barron-Gafford G Griffith A Alpert H Van Gestel N Robertson T Huxman TE Zak J Loik ME Tissue D 《Oecologia》2007,151(4):704-718
Global climate models predict that in the next century precipitation in desert regions of the USA will increase, which is
anticipated to affect biosphere/atmosphere exchanges of both CO2 and H2O. In a sotol grassland ecosystem in the Chihuahuan Desert at Big Bend National Park, we measured the response of leaf-level
fluxes of CO2 and H2O 1 day before and up to 7 days after three supplemental precipitation pulses in the summer (June, July, and August 2004).
In addition, the responses of leaf, soil, and ecosystem fluxes of CO2 and H2O to these precipitation pulses were also evaluated in September, 1 month after the final seasonal supplemental watering event.
We found that plant carbon fixation responded positively to supplemental precipitation throughout the summer. Both shrubs
and grasses in watered plots had increased rates of photosynthesis following pulses in June and July. In September, only grasses
in watered plots had higher rates of photosynthesis than plants in the control plots. Soil respiration decreased in supplementally
watered plots at the end of the summer. Due to these increased rates of photosynthesis in grasses and decreased rates of daytime
soil respiration, watered ecosystems were a sink for carbon in September, assimilating on average 31 mmol CO2 m−2 s−1 ground area day−1. As a result of a 25% increase in summer precipitation, watered plots fixed eightfold more CO2 during a 24-h period than control plots. In June and July, there were greater rates of transpiration for both grasses and
shrubs in the watered plots. In September, similar rates of transpiration and soil water evaporation led to no observed treatment
differences in ecosystem evapotranspiration, even though grasses transpired significantly more than shrubs. In summary, greater
amounts of summer precipitation may lead to short-term increased carbon uptake by this sotol grassland ecosystem. 相似文献
4.
Arid and semi-arid ecosystems of the southwestern US are undergoing changes in vegetation composition and are predicted to
experience shifts in climate. To understand implications of these current and predicted changes, we conducted a precipitation
manipulation experiment on the Santa Rita Experimental Range in southeastern Arizona. The objectives of our study were to
determine how soil surface and seasonal timing of rainfall events mediate the dynamics of leaf-level photosynthesis and plant
water status of a native and non-native grass species in response to precipitation pulse events. We followed a simulated precipitation
event (pulse) that occurred prior to the onset of the North American monsoon (in June) and at the peak of the monsoon (in
August) for 2002 and 2003. We measured responses of pre-dawn water potential, photosynthetic rate, and stomatal conductance
of native (Heteropogon contortus) and non-native (Eragrostis lehmanniana) C4 bunchgrasses on sandy and clay-rich soil surfaces. Soil surface did not always amplify differences in plant response to a
pulse event. A June pulse event lead to an increase in plant water status and photosynthesis. Whereas the August pulse did
not lead to an increase in plant water status and photosynthesis, due to favorable soil moisture conditions facilitating high
plant performance during this period. E. lehmanniana did not demonstrate heightened photosynthetic performance over the native species in response to pulses across both soil
surfaces. Overall accumulated leaf-level CO2 response to a pulse event was dependent on antecedent soil moisture during the August pulse event, but not during the June
pulse event. This work highlights the need to understand how desert species respond to pulse events across contrasting soil
surfaces in water-limited systems that are predicted to experience changes in climate. 相似文献
5.
Beesley J Pickett HA Johnatty SE Dunning AM Chen X Li J Michailidou K Lu Y Rider DN Palmieri RT Stutz MD Lambrechts D Despierre E Lambrechts S Vergote I Chang-Claude J Nickels S Vrieling A Flesch-Janys D Wang-Gohrke S Eilber U Bogdanova N Antonenkova N Runnebaum IB Dörk T Goodman MT Lurie G Wilkens LR Matsuno RK Kiemeney LA Aben KK Marees T Massuger LF Fridley BL Vierkant RA Bandera EV Olson SH Orlow I Rodriguez-Rodriguez L Cook LS Le ND Brooks-Wilson A Kelemen LE Campbell I Gayther SA Ramus SJ 《PloS one》2011,6(9):e24987
Genetic variation at the TERT-CLPTM1L locus at 5p15.33 is associated with susceptibility to several cancers, including epithelial ovarian cancer (EOC). We have carried out fine-mapping of this region in EOC which implicates an association with a single nucleotide polymorphism (SNP) within the TERT promoter. We demonstrate that the minor alleles at rs2736109, and at an additional TERT promoter SNP, rs2736108, are associated with decreased breast cancer risk, and that the combination of both SNPs substantially reduces TERT promoter activity. 相似文献
6.
Farkas V Vass E Hanssens I Majer Z Hollósi M 《Bioorganic & medicinal chemistry》2005,13(17):5310-5320
A series of cyclic peptides with different linkers were designed and synthesized to model the elbow-type Ca2+-binding loop of alpha-lactalbumin (LA). All amino acids of the Ca2+-binding loop are strikingly well conserved among LAs of different species with the sequence Lys79-Phe-Leu-Asp82-Asp-Asp-Leu-Thr- Asp87-Asp88, where three carboxylates of Asp82, Asp87, and Asp88 and the amide carbonyl oxygen atoms of Lys79 and Asp84 participate in Ca2+ binding. Alanine-containing models were also prepared for monitoring the role of the binding (82, 87-88) and nonbinding Asp residues (83-84) in coordinating the cation. The structural features of synthetic peptides and their Ca2+-binding properties were investigated in solution by circular dichroism (CD) and Fourier transform infrared (FTIR) spectroscopy. In water, the CD curves show a strong negative band below 200 nm as a sign of the presence of unfolded conformers. In TFE, all cyclic peptides were found to have a CD spectrum, reflecting the presence of folded (turn) conformers. The effect of Ca2+ was dependent on the structure and concentration of the model and the Ca2+ to peptide ratio (r(cat)). A surprising time dependence of the FTIR spectra of Ca2+ complexes of the Ala-containing peptides was observed. The shape of the broad amide I band showed no more change after approximately 60 min. Contrary to this, the deprotonation of the side chain COOH group(s) and formation of the final coordination sphere of Ca2+ took more time. Infrared spectra showed that in the Ca2+ complex of model comprising the binding Asp residues of LA, the cation is coordinated to the COO- groups of all three Asps, while in the complex of model comprising nonbinding Asp residues of LA, the two neighboring Asp side chains form a bridged Ca2+-binding system. 相似文献
7.
The Sequence Alignment Benchmark (SABmark) provides sets of multiple alignment problems derived from the SCOP classification. These sets, Twilight Zone and Superfamilies, both cover the entire known fold space using sequences with very low to low, and low to intermediate similarity, respectively. In addition, each set has an alternate version in which unalignable but apparently similar sequences are added to each problem. 相似文献
8.
Desmet J Meersseman G Boutonnet N Pletinckx J De Clercq K Debulpaep M Braeckman T Lasters I 《Proteins》2005,58(1):53-69
The study of intermolecular interactions is a fundamental research subject in biology. Here we report on the development of a quantitative structure-based affinity scoring method for peptide-protein complexes, named PepScope. The method operates on the basis of a highly specific force field function (CHARMM) that is applied to all-atom structural representations of peptide-receptor complexes. Peptide side-chain contributions to total affinity are scored after detailed rotameric sampling followed by controlled energy refinement. A de novo approach to estimate dehydration energies was developed, based on the simulation of individual amino acids in a solvent box filled with explicit water molecules. Transferability of the method was demonstrated by its application to the hydrophobic HLA-A2 and -A24 receptors, the polar HLA-A1, and the sterically ruled HLA-B7 receptor. A combined theoretical and experimental study on 39 anchor substitutions in FxSKQYMTx/HLA-A2 and -A24 complexes indicated a prediction accuracy of about two thirds of a log-unit in Kd. Analysis of free energy contributions identified a great role of desolvation and conformational strain effects in establishing a given specificity profile. Interestingly, the method rightly predicted that most anchor profiles are less specific than so far assumed. This suggests that many potential T-cell epitopes could be missed with current prediction methods. The results presented in this work may therefore significantly affect T-cell epitope discovery programs applied in the field of peptide vaccine development. 相似文献
9.
Homologous gene recombination is crucial for the repair of DNA. A superfamily of recombinases facilitate a central strand exchange reaction in the repair process. This reaction is initiated by coating single-stranded DNA (ssDNA) with recombinases in the presence of ATP and Mg(2+) co-factors to form helical nucleoprotein filaments with elevated ATPase and strand invasion activities. At the amino acid sequence level, archaeal RadA and Rad51 and eukaryal Rad51 and meiosis-specific DMC1 form a closely related group of recombinases distinct from bacterial RecA. Unlike the extensively studied Escherichia coli RecA (EcRecA), increasing evidences on yeast and human recombinases imply that their optimal activities are dependent on the presence of a monovalent cation, particularly potassium. Here we present the finding that archaeal RadA from Methanococcus voltae (MvRadA) is a stringent potassium-dependent ATPase, and the crystal structure of this protein in complex with the non-hydrolyzable ATP analog adenosine 5'-(beta,gamma-iminotriphosphate), Mg(2+), and K(+) at 2.4 A resolution. Potassium triggered an in situ conformational change in the ssDNA-binding L2 region concerted with incorporation of two potassium ions at the ATPase site in the RadA crystals preformed in K(+)-free medium. Both potassium ions were observed in contact with the gamma-phosphate of the ATP analog, implying a direct role by the monovalent cations in stimulating the ATPase activity. Cross-talk between the ATPase site and the ssDNA-binding L2 region visualized in the MvRadA structure provides an explanation to the co-factor-induced allosteric effect on RecA-like recombinases. 相似文献
10.