title: Direct incorporation of experimental phase information in model refinement.
abstract: The incorporation of prior phase information into a maximum-likelihood formalism has been shown to strengthen model refinement. However, the currently available likelihood refinement target using prior phase information has shortcomings; the 'phased' refinement target considers experimental phase information indirectly and statically in the form of Hendrickson-Lattman coefficients. Furthermore, the current refinement target implicitly assumes that the prior phase information is independent of the calculated model structure factor. This paper describes the derivation of a multivariate likelihood function that overcomes these shortcomings and directly incorporates experimental phase information from a single-wavelength anomalous diffraction (SAD) experiment. This function, which simultaneously refines heavy-atom and model parameters, has been implemented in the refinement program REFMAC5. The SAD function used in conjunction with the automated model-building procedures of ARP/wARP leads to a successful solution when current likelihood functions fail in a test case shown.
authors.affiliation: Biophysical Structural Chemistry, Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, PO Box 9502, 2300 RA Leiden, The Netherlands.
authors.forename: Pavol
authors.initials: P
authors.lastname: Skubák
authors.forename: Garib N
authors.initials: GN
authors.lastname: Murshudov
authors.forename: Navraj S
authors.initials: NS
authors.lastname: Pannu
mesh_terms: D000465:Algorithms; D019295:Computational Biology; D018360:Crystallography, X-Ray; D016013:Likelihood Functions; D008958:Models, Molecular; D012542:Scattering, Radiation; D020860:Subtilisin / Q000737:chemistry
chemical_list: D020860:Subtilisin