SAD phasing at Bijvoet ratio below 0.6%

Abstract

METHODS FOR STRUCTURE DETERMINATION C154 generated, and they form covalent bonds at the ortho-positions of accessible tyrosine residues by the aromatic electrophilic substitution. The resultant iodine derivatives are the most suitable for in-house phasing using longer wavelength X-rays, such as Cr-Ka X-rays, because anomalous signals of iodine are strengthen at the region of longer wavelength X-rays. We applied this approach to native crystals of thaumatin. The crystals were successfully iodinated to generate enough phasing power by the Cr-Ka X-rays. As a result, the crystal structure of the iodinated thaumatin was solved by fully automated procedure. The present methods not only to contribute to the in-house ab initio structure determinations using Cr-Ka radiation, but also to promote the phasing at synchrotron facilities if their beamlines provide longer wavelengths than the conventional ones. In the poster session, the possibility of the present method to apply for other crystals will be discussed.