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Heavy-atom Derivatization (heavy-atom + derivatization)
Selected AbstractsWith phases: how two wrongs can sometimes make a rightACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2010Pietro Roversi In isolation, both weak isomorphous/anomalous difference signals from heavy-atom derivatization and phases from partial molecular-replacement solutions for a subset of the asymmetric unit often fall short of producing interpretable electron-density maps. Phases generated from very partial molecular-replacement models (if generated carefully) can be used to reliably locate heavy-atom sites, even if the signal is not sufficiently strong to allow robust finding of the sites using Patterson interpretation or direct methods. Additional advantages are that using molecular-replacement phases to define the heavy-atom substructure avoids the need for subsequent hand determination and/or origin-choice reconciliation and that the partial model can be used to aid the mask determination during solvent flattening. Two case studies are presented in which it was only by combining experimental and molecular-replacement phasing approaches that the crystal structures could be determined. [source] Getting the best out of long-wavelength X-rays: de novo chlorine/sulfur SAD phasing of a structural protein from ATVACTA CRYSTALLOGRAPHICA SECTION D, Issue 3 2010Adeline Goulet The structure of a 14,kDa structural protein from Acidianus two-tailed virus (ATV) was solved by single-wavelength anomalous diffraction (SAD) phasing using X-ray data collected at 2.0,Å wavelength. Although the anomalous signal from methionine sulfurs was expected to suffice to solve the structure, one chloride ion turned out to be essential to achieve phasing. The minimal data requirements and the relative contributions of the Cl and S atoms to phasing are discussed. This work supports the feasibility of a systematic approach for the solution of protein crystal structures by SAD based on intrinsic protein light atoms along with associated chloride ions from the solvent. In such cases, data collection at long wavelengths may be a time-efficient alternative to selenomethionine substitution and heavy-atom derivatization. [source] Using barium ions for heavy-atom derivatization and phasing of xylanase II from Trichoderma longibrachiatumACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2007Natalia Moiseeva This paper describes the use of barium chloride to produce a heavy-atom derivative of xylanase II crystals from Trichoderma longibrachiatum, which was obtained either by cocrystallization or soaking. SAD phasing led to interpretable electron-density maps that allowed unambiguous chain tracing. In the best case, with a data set collected at 9.5,keV, 88% of the residues were built, with 83% of the side chains assigned. The barium ions are found to mainly interact with main-chain carbonyl groups and water molecules. It is suggested that barium ions could also be used as a potential anomalous scatterer in the quick cryosoaking procedure for phasing. [source] Crystallization and heavy-atom derivatization of StHsp14.0, a small heat-shock protein from Sulfolobus tokodaiiACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 10 2009Takuro Hayashi Small heat-shock proteins (sHsps) bind and stabilize proteins denatured by heat or other stresses in order to prevent unfavourable protein aggregation. StHsp14.0 is an sHsp found in the acidothermophilic archaeon Sulfolobus tokodaii. A variant of StHsp14.0 was crystallized by the sitting-drop vapour-diffusion method. The crystals diffracted X-rays to 1.85,Å resolution and belonged to space group P21212, with unit-cell parameters a = 40.4, b = 61.1, c = 96.1,Å. The VM value was estimated to be 2.1,Å3,Da,1, assuming the presence of two molecules in the asymmetric unit. Heavy-atom derivative crystals were prepared successfully by the cocrystallization method and are isomorphic to native crystals. [source] | ||||||||||