Calculated properties of the active site complex of oxidized rubredoxins

Abstract

In rubredoxins, the simplest class of iron-sulfur, electron-transport proteins, the center of biological activity is a single Fe atom which is surrounded by a distorted tetrahedral array of four cysteine sulfur atoms. In addition to its electron-transport characteristics, a number of physical properties of these proteins have been determined, all of which depend crucially on the conformation and electron distribution and energy of the active site complex. Thus, in this initial study, using a semi-empirical MO program called Iterative Extended Huckel Theory (IEHT), we have calculated the variation in electron distribution and energies of the Fe-S active site complex as a function of its conformation. Ten conformers were chosen which span a symmetry range from that determined by X-Ray crystal structure analysis to an idealized regular tetrahedral symmetry. The differences in electron distribution and electronic energies obtained for these 10 conformers are reflected in all observable properties of the protein calculation of these properties, using the results reported here, are the subject of our subsequent papers in this series.