Crystallographic structure determination of cytochrome f at 1.96 angstrom resolution
Abstract
The cytochrome $b\sb6f$ complex connects the two reaction centers in oxygenic photosynthesis. The crystal structure of the reduced redox-active 252 residue lumen-side domain of the 285 residue cytochrome f of the $b\sb6f$ complex was solved and refined at a resolution of 1.96 A. It is the first polypeptide structure of the $b\sb6f$ or $bc\sb1$ complexes to be determined at the atomic level. Cytochrome f contains two domains in an elongate (75 A x 35 A x 24 A) structure whose secondary structure is mostly $\beta$ sheet. The covalently bound heme lies within the larger domain near the interface between the two domains. The smaller domain (residues 169-231) is postulated to contribute to the plastocyanin binding site. The axial sixth heme ligand is the $\alpha$-amino group of the N-terminal tyrosine residue. N-terminal amino group ligation in a heme protein has not been previously observed. The larger domain has the fibronectin type III domain that is present in many animal proteins. It is a new fold for a cytochrome structure. A chain of five internal water molecules is present. These waters are in an "L" shaped arrangement, with the corner water H-bonded to the N$\delta1$ of His 25, a heme Fe ligand. It is suggested this chain acts as a proton wire during proton translocation by the $b\sb6f$ complex.
Degree
Ph.D.
Advisors
Smith, Purdue University.
Subject Area
Biophysics
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