Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 6, Pages 1738-1743Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0507179103
Keywords
metal site structure; metalloproteins; paramagnetic nuclear relaxation
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The biological function of metalloproteins is closely tied to the geometric and electronic structures of the metal sites. Here, we show that the geometric structure of the metal site of a metalloprotein in solution can be determined from experimentally measured electron-nuclear spin-spin interactions obtained by NMR. Thus, the geometric metal site structure of plastocyanin from Anabaena variabilis was determined by including the paramagnetic relaxation enhancement of protons close to the copper site as restraints in a conventional NMR structure determination, together with the distribution of the unpaired electron onto the ligand atoms. Also, the interproton distances (nuclear Overhauser enhancements) and dihedral angles (scalar nuclear spin-spin couplings) normally used in NMR structure determinations were included as restraints. The structure calculations were carried out with the program X-PLOR and a module that takes into account the specific characteristics of the paramagnetic restraints. A well defined metal site structure was obtained with the structural characteristics of the blue copper site, including a distorted tetrahedral geometry, a short Cu-Cys S-gamma bond, and a long Cu-Met S-delta bond. Overall, the agreement of the obtained metal site structure of Anabaena variabilis plastocyanin with those of other plastocyanins obtained by x-ray crystallography confirms the reliability of the approach.
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