Structure determination of the molybdenum iron protein of nitrogenase at 2.2 angstrom resolution
Abstract
The three dimensional structure of the MoFe proteins from Azotobacter vinelandii (Av1) and Clostridium pasteurianum (Cp1) have been determined by X-ray diffraction methods. This thesis describes initial work on the structure of Cp1, and detailed descriptions of the structure of Av1. The protein is an $\alpha2\beta2$ tetramer of total molecular weight 220,000 Daltons. Each tetramer binds two copies of two unusual metal-sulfur cofactors, a Mo-Fe-S containing cluster (FeMoco) and an Fe-S cluster (P-cluster). Both the $\alpha$- and $\beta$-subunits are folded into three identical parallel 4-stranded $\beta$-sheet domains. The refinement of the Av1 protein against 2.2 A diffraction data has yielded a crystallographic R-value of 17.5%, with acceptable polypeptide model geometry. The current Av1 model contains two copies each of the $\alpha$-subunits (residues 5-480) and the entire $\beta$-subunit, along with a (MoFe$\rm\sb7S\sb9$) cluster with homocitrate bound to the Mo atom for FeMoco, and an (Fe$\rm\sb8S\sb7$) model for the P-cluster.
Degree
Ph.D.
Subject Area
Biochemistry
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