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Multiple-wavelength Anomalous Diffraction (multiple-wavelength + anomalous_diffraction)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

Structures of Four Crystal Forms of Decaplanin

HELVETICA CHIMICA ACTA, Issue 5 2003
Christopher Lehmann
The glycopeptide antibiotic decaplanin (1; formerly known as MM 47761 and M86-1410) crystallizes in two P21 and two P6122 crystal forms, each with four monomers in the asymmetric unit, with solvent contents varying from 48 to 69%. Although with ca. 600 unique atoms, the structures are larger than typical small molecules, one was solved by direct methods. The other three were solved by typical macromolecular methods: single-wavelength anomalous diffraction (SAD) of the Cl-atoms present naturally in the structure, multiple-wavelength anomalous diffraction (MAD) at the Br absorption edge for a crystal soaked in NaBr solution, and molecular replacement. There is evidence of appreciable radiation damage with loss of 20,30% of the covalent and ionic halogens affecting the synchrotron datasets that may even have unintentionally facilitated the MAD structure solution. The structures contain the dimer units typical of antibiotics related to vancomycin, but, in addition, there are a variety of further intermolecular interactions responsible for the polymorphy leading to intertwined 61 -helices in two of the crystal forms. Except for the sugars and some sidechains, the conformations of the 16 independent monomers are very similar. [source]

Enhancing MAD FA data for substructure determination

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2010
Hongliang Xu
Heavy-atom substructure determination is a critical step in phasing an unknown macromolecular structure. Dual-space (Shake-and-Bake) recycling is a very effective procedure for locating the substructure (heavy) atoms using FA data estimated from multiple-wavelength anomalous diffraction. However, the estimated FA are susceptible to the accumulation of errors in the individual intensity measurements at several wavelengths and from inaccurate estimation of the anomalous atomic scattering corrections f, and f,,. In this paper, a new statistical and computational procedure which merges multiple FA estimates into an averaged data set is used to further improve the quality of the estimated anomalous amplitudes. The results of 18 Se-atom substructure determinations provide convincing evidence in favor of using such a procedure to locate anomalous scatterers. [source]

Crystallization and rhenium MAD phasing of the acyl-homoserinelactone synthase EsaI

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 12 2001
William T. Watson
Acyl-homoserine- l -lactones (AHLs) are diffusible chemical signals that are required for virulence of many Gram-negative bacteria. AHLs are produced by AHL synthases from two substrates, S -adenosyl- l -methionine and acyl-acyl carrier protein. The AHL synthase EsaI, which is homologous to the AHL synthases from other pathogenic bacterial species, has been crystallized in the primitive tetragonal space group P43, with unit-cell parameters a = b = 66.40, c = 47.33,Å. The structure was solved by multiple-wavelength anomalous diffraction with a novel use of the rhenium anomalous signal. The rhenium-containing structure has been refined to a resolution of 2.5,Å and the perrhenate ion binding sites and liganding residues have been identified. [source]

Structure of Lmaj006129AAA, a hypothetical protein from Leishmania major

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2006
Tracy Arakaki
The gene product of structural genomics target Lmaj006129 from Leishmania major codes for a 164-residue protein of unknown function. When SeMet expression of the full-length gene product failed, several truncation variants were created with the aid of Ginzu, a domain-prediction method. 11 truncations were selected for expression, purification and crystallization based upon secondary-structure elements and disorder. The structure of one of these variants, Lmaj006129AAH, was solved by multiple-wavelength anomalous diffraction (MAD) using ELVES, an automatic protein crystal structure-determination system. This model was then successfully used as a molecular-replacement probe for the parent full-length target, Lmaj006129AAA. The final structure of Lmaj006129AAA was refined to an R value of 0.185 (Rfree = 0.229) at 1.60,Å resolution. Structure and sequence comparisons based on Lmaj006129AAA suggest that proteins belonging to Pfam sequence families PF04543 and PF01878 may share a common ligand-binding motif. [source]