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Staphylococcal Nuclease (staphylococcal + nuclease)

Distribution by Scientific Domains
Chemistry100%

Selected Abstracts

The small-angle and wide-angle X-ray scattering set-up at beamline BL9 of DELTA

JOURNAL OF SYNCHROTRON RADIATION, Issue 3 2007
Christina Krywka
The multi-purpose experimental endstation of beamline BL9 at the Dortmund Electron Accelerator (DELTA) is dedicated to diffraction experiments in grazing-incidence geometry, reflectivity and powder diffraction measurements. Moreover, fluorescence analysis and inelastic X-ray scattering experiments can be performed. Recently, a new set-up for small-angle and wide-angle X-ray scattering utilizing detection by means of an image-plate scanner was installed and is described in detail here. First small-angle X-ray scattering experiments on aqueous solutions of lysozyme with different cosolvents and of staphylococcal nuclease are discussed. The application of the set-up for texture analysis is emphasized and a study of the crystallographic texture of natural bio-nanocomposites, using lobster and crab cuticles as model materials, is presented. [source]

Effects of denaturants and substitutions of hydrophobic residues on backbone dynamics of denatured staphylococcal nuclease

PROTEIN SCIENCE, Issue 7 2003
Satoshi Ohnishi
NOE, nuclear Overhauser effect; RDC, residual dipolar coupling Abstract Analysis of residual dipolar couplings (RDCs) in the ,131, fragment of staphylococcal nuclease has demonstrated that its ensemble-averaged structure is resistant to perturbations such as high concentrations of urea, low pH, and substitution of hydrophobic residues, suggesting that its residual structure is encoded by local side-chain/backbone interactions. In the present study, the effects of these same perturbations on the backbone dynamics of ,131, were examined through 1H- 15N relaxation methods. Unlike the global structure reported by RDCs, the transverse relaxation rates R2 were quite sensitive to denaturing conditions. At pH 5.2, ,131, exhibits an uneven R2 profile with several characteristic peaks involving hydrophobic chain segments. Protonation of carboxyl side chains by lowering the pH reduces the values of R2 along the entire chain, yet these characteristic peaks remain. In contrast, high concentrations of urea or the substitution of 10 hydrophobic residues eliminates these peaks and reduces the R2 values by a greater amount. The combination of low pH and high urea leads to further decreases in R2. These denaturant-induced increases in backbone mobility are also reflected in decreases in 15N NOEs and in relaxation interference parameters, with the former reporting an increase in fast motions and the latter a decrease in slow motions. Comparison between the changes in chain dynamics and the corresponding changes in Stokes radius and the patterns of RDCs suggests that regional variations in backbone dynamics in denatured nuclease arise primarily from local contacts between hydrophobic side chains and local interactions involving charged carboxyl groups. [source]

Distance dependence and salt sensitivity of pairwise, coulombic interactions in a protein

PROTEIN SCIENCE, Issue 5 2002
Kelly K. Lee
Abstract Histidine pKa values were measured in charge-reversal (K78E, K97E, K127E, and K97E/K127E) and charge-neutralization (E10A, E101A, and R35A) mutants of staphylococcal nuclease (SNase) by 1H-NMR spectroscopy. Energies of interaction between pairs of charges (,Gij) were obtained from the shifts in pKa values relative to wild-type values. The data describe the distance dependence and salt sensitivity of pairwise coulombic interactions. Calculations with a continuum electrostatics method captured the experimental ,Gij when static structures were used and when the protein interior was treated empirically with a dielectric constant of 20. The ,Gij when rij , 10 Å were exaggerated slightly in the calculations. Coulomb's law with a dielectric constant near 80 and a Debye-Hückel term to account for screening by the ionic strength reproduced the salt sensitivity and distance dependence of ,Gij as well as the structure-based method. In their interactions with each other, surface charges behave as if immersed in water; the Debye length describes realistically the distance where interactions become negligible at a given ionic strength. On average, charges separated by distances (rij) ,5 Å interacted with ,Gij , 0.6 kcal/mole in 0.01 M KCl, but ,Gij decayed to ,0.10 kcal/mole when rij = 20 Å. In 0.10 M KCl, ,Gij , 0.10 kcal/mole when rij = 10 Å. In 1.5 M KCl, only short-range interactions with rij , 5 Å persisted. Although at physiological ionic strengths the interactions between charges separated by more than 10 Å are extremely weak, in situations where charge imbalance exists many weak interactions can cumulatively produce substantial effects. [source]

On the Temperature,Pressure Free-Energy Landscape of Proteins

CHEMPHYSCHEM, Issue 4 2003
Revanur Ravindra Dr.
Abstract We studied the thermodynamic stability of a small monomeric protein, staphylococcal nuclease (Snase), as a function of both temperature and pressure, and expressed it as a 3D free-energy surface on the p,T -plane using a second-order Taylor expansion of the Gibbs free-energy change ,G upon unfolding. We took advantage of a series of different techniques (small-angle Xray scattering, Fourier-transform infrared spectroscopy, differential thermal analysis, pressure perturbation calorimetry and densitometry) in the evaluation of the conformation of the protein and in evaluating the changes in the thermodynamic parameters upon unfolding, such as the heat capacity, enthalpy, entropy, volume, isothermal compressibility and expansivity. The calculated results of the free-energy landscape of the protein are in good agreement with experimental data of the p,T -stability diagram of the protein over a temperature range from 200 to 400 K and at pressures from ambient pressure to 4000 bar. The results demonstrate that combined temperature,pressure-dependent studies can help delineate the free-energy landscape of proteins and hence help elucidate which features and thermodynamic parameters are essential in determining the stability of the native conformational state of proteins. The approach presented may also be used for studying other systems with so-called re-entrant or Tamman loop-shaped phase diagrams. [source]