Multivariate estimation of substructure amplitudes for a single-wavelength anomalous diffraction experiment

Acta Crystallographica Section D Structural Biology, vol. 79, pp. 339–344

Abstract

To determine a substructure from single-wavelength anomalous diffraction (SAD) data using Patterson or direct methods, the substructure-factor amplitude (| F a |) is first estimated. Currently, the absolute value of the Bijvoet difference is widely used as an estimate of | F a | values for SAD data. Here, an equation is derived from multivariate statistics and tested that takes into account the correlation between the observed positive ( F + ) and negative ( F − ) Friedel pairs and F a along with measurement errors in the observed data. The multivariate estimation of | F a | has been implemented in a new program, Afro . Results on over 180 test cases show that Afro provides a higher correlation to the final substructure-factor amplitudes (calculated from the refined, final substructures) than the Bijvoet differences and improves the robustness of direct-methods substructure detection.

Authors 1

1. Pavol Skubák Aachen Department of Infectious Diseases

   Leiden University Medical Center

   Affiliation as printed

   Department of Infectious Diseases, Leiden University Medical Center, Albinusdreef 2, 2333 ZA, Leiden, The Netherlands