X-Ray Crystal and Exafs Studies of Ps Dentrifications AZ

Korszun, Zbigniew

Abstract

The x-ray crystal structure of azurin from Ps. denitrificans, a blue Cu protein whose function is electron transfer, will be solved by anomalous dispersion phasing from intrinsic protein atoms. Synchrotron radiation which provides x-rays from approximately 4 to 80 KeV will be used in conjunction with a suitably focusing double crystal monochromator to collect Cu diffraction data at 8.98 KeV and S diffraction data at 4.00 KeV. These intensity measurements will be combined with measurements made at 8.03 KeV (the KuKAlpha emission line) to exploit the large differences in Deltaf' and Deltaf"""""""" for Cu and the increased value of Deltaf"""""""" for S. Measurement of Freidel pairs at one energy in combination with measurement of differences in intensity as a function of energy will be used to locate the anomalous scatterers. The anomalous dispersion phases will be used in conjunction with partial structure phases resulting from the known S and Cu positions to calculate an electron density map of the entire protein. The uniqueness and generality of these phasing methods will establish multiple wavelength diffraction as a routine protein crystallographic method. EXAFS studies on both the oxidized and reduced species of azurin will parallel the crystal experiments. The EXAFS studies will provide precise bond lengths for the Cu ligands in both the oxidized and reduced states fo the molecule. Together, these studies will yield structural information about the Type 1 copper proteins which will facilitate the understanding of the unique biochemical and spectroscopic properties and their function.