NMR Determination of the Magnetic Susceptibility Anisotropy of Cytochrome c' of Rhodobacter Capsulatus by ~1J_(HN) Dipolar Coupling Constants Measurement: Characterization of Its Monomeric State in Solution

摘要

~1J_(NH) splittings have been measured at 600 and 400 MHz on the paramagnetic (s = 2 and S = 5/2) and on the diamagnetic state (S = 0) of cytochrome c' of Rhodobacter capsulatus. Residual dipolar splittings and the magnetic susceptibility tensor have been then derived using two methods. The first method equaled for a paramagnetic species the dipolar splitting to the difference of the measured ~1J_(NH) splittings between the paramagnetic and diamagnetic forms at one field. The second method consisted in deriving the total magnetic tensor of the paramagnetic forms from the splittings at two fields with a post-correction for the diamagnetic contribution. Both methods are shown to produce equivalent results for the determination of the susceptibility magnetic tensor. Comparison with the magnetic tensor obtained with a previous study based on the dipolar shifts leads to the evidence that, unlike most other cytochromes c', Rb. capsulatus cytochrome c' of strain M1131 is monomeric in solution. This result is discussed in view of the cytochrome c' function, Our study confirms that dipolar splittings are a powerful tool for structure determination, providing insight not only into local structural details but also into the global fold of molecules.