Metalloprotein active site structure determination: Synergy between X-ray absorption spectroscopy and X-ray crystallography

Structures of metalloprotein active sites derived from X-ray crystallography frequently contain chemical anomalies such as unexpected atomic geometries or elongated bond-lengths. Such anomalies are expected from the known errors inherent in macromolecular crystallography (ca. 0.1–0.2 Å) and from the lack of appropriate restraints for metal sites which are often without precedent in the small molecule structure literature. Here we review the potential of X-ray absorption spectroscopy to provide information and perspective which could aid in improving the accuracy of metalloprotein crystal structure solutions. We also review the potential problem areas in analysis of the extended X-ray absorption fine structure (EXAFS) and discuss the use of density functional theory as another possible source of geometrical restraints for crystal structure analysis of metalloprotein active sites.

X-ray absorption spectroscopy can provide constraints for crystallographic structure solution of the active sites of metalloproteins.Figure optionsDownload as PowerPoint slideHighlights
► X-ray absorption spectroscopy (XAS) is used to study metal structure in proteins.
► XAS complements crystallography in providing structural detail.
► XAS can provide constraints and restraints to improve structure solutions.
► Strengths, limitations and synergies of XAS and crystallography are reviewed.