NMR Research Today is a free monthly online journal that collates and summarizes the latest research about NMR, including details on nuclear magnetic resonance, structural determination, techniques. | ||||||||
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Reinvestigation of the method used to map the electronic structure of blue copper proteins by NMR relaxation.Flemming Hansen D, Gorelsky SI, Sarangi R, Hodgson KO, Hedman B, Christensen HE, Solomon EI, Led JJ Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark. A previous method for mapping the electron spin distribution in blue copper proteins by paramagnetic nuclear magnetic resonance (NMR) relaxation (Hansen DF, Led JJ, 2004, J Am Chem Soc 126:1247-1253) suggested that the blue copper site of plastocyanin from Anabaena variabilis (A.v.) is less covalent than those found for other plastocyanins by other experimental methods, such as X-ray absorption spectroscopy. Here, a detailed spectroscopic study revealed that the electronic structure of A.v. plastocyanin is similar to those of other plastocyanins. Therefore, the NMR approach was reinvestigated using a more accurate geometric structure as the basis for the mapping, in contrast to the previous approach, as well as a more complete spin distribution model including Gaussian-type natural atomic orbitals instead of Slater-type hydrogen-like atomic orbitals. The refinement results in a good agreement between the electron spin density derived from paramagnetic NMR and the electronic structure description obtained by the other experimental methods. The refined approach was evaluated against density functional theory (DFT) calculations on a model complex of the metal site of plastocyanin in the crystal phase. In general, the agreement between the experimental paramagnetic relaxation rates and the corresponding rates obtained by the DFT calculations is good. Small deviations are attributed to minor differences between the solution structure and the crystal structure outside the first coordination sphere. Overall, the refined approach provides a complementary experimental method for determining the electronic structure of paramagnetic metalloproteins, provided that an accurate geometric structure is available. Published 4 April 2006 in J Biol Inorg Chem, 11(3): 277-85.
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