Use of CrK alpha radiation to enhance the signal from anomalous scatterersincluding sulfur

Citation
W. Kwiatkowski et al., Use of CrK alpha radiation to enhance the signal from anomalous scatterersincluding sulfur, J APPL CRYS, 33(2), 2000, pp. 876-881
Citations number
30
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF APPLIED CRYSTALLOGRAPHY
ISSN journal
0021-8898 → ACNP
Volume
33
Issue
2
Year of publication
2000
Part
3
Pages
876 - 881
Database
ISI
SICI code
0021-8898(20000601)33:2<876:UOCART>2.0.ZU;2-X
Abstract
The anomalous signals from scatterers such as sulfur (S) and arsenic (As) w ere compared in diffraction data sets collected from an X-ray source with t hree different targets, Au, Cu and Cr, on a multi-target rotating anode. HI V-1 integrase crystals served as the test case for this study. The crystall ine specimen of HIV-1 integrase contains in each protein molecule two As at oms, each covalently bound to a cysteine S atom, and two additional S atoms derived from methionine. It was found that the Cr K alpha radiation gave t he clearest peaks in anomalous difference Fourier maps, although the signal -to-noise ratios of the anomalous signal for the Cu K alpha and Cr K alpha data were similar but better than that for Au L alpha. This result was in s pite of the fourfold higher flux from the Cu anode versus the Cr anode. For all three X-ray wavelengths, anomalous difference Fourier maps calculated with bias-removed phases derived from the known atomic model revealed clear peaks at the two As sites. However, only in the map calculated using the C r K alpha data were both peaks of the expected ellipsoidal shape, envelopin g the As atom and the adjacent S atom. None of the S sites was apparent in difference maps calculated using the Au L alpha data. The ability to enhanc e the S-derived anomalous signal using Cr K alpha radiation has particularl y useful applications in the structure determination of proteins, for examp le in resolving ambiguities in the chain tracing of a protein with numerous disulfide bonds and in assigning amino acid identities. Additionally, anom alous difference Patterson maps calculated from the Cr K alpha data were su fficiently clear to identify the As-related peaks. These results form the g roundwork for in-house phase determination with the multi-wavelength anomal ous diffraction method.