Hemeproteins: Recent Advances in Quantitative XANES Analysis

Recently, we have shown that multiple scattering (MS) theory, via the MXAN package, is able to reproduce the experimental X-ray absorption near edge structure (XANES) data of biological samples, in particular hemeproteins, from the rising edge up to similar to 150-200 eV above the edge. In the present work, we illustrate how XANES can be used either as an independent tool to provide bond-lengths and bond-angles for a metalloprotein active site in solution, or in combination with X-ray Diffraction for structural determinations of ligand binding geometry of the same diffracting protein crystal, providing atomic precision even for crystallographic structures solved at > 1.2 angstrom resolution. At low temperature, XANES can be applied to provide the Fe-heme structure of trapped intermediate conformations; of fight triggered processes, and some aspects of the ligand binding dynamics. Very recently, XANES difference spectra have been analyzed to provide the Fe-heme structure of multiple intermediates of carbonmonoxy-myoglobin, obtained under different photolysis protocols in solution state