Rotational Diffusion Anisotropy and Local Backbone Dynamics of Carbon Monoxide-Bound Rhodobacter capsulatus Cytochrome c‘

The rotational diffusion and backbone dynamics of the carbon monoxide-bound Rhodobacter capsulatus cytochrome c‘ have been investigated using heteronuclear NMR spectroscopy. This protein consists of a four-helix bundle motif and a histidine-heme binding domain and has been shown to form a symmetric dimer in the crystal state. 15N relaxation measurements reveal that an asymmetric tensor is necessary to describe overall rotational diffusion of the protein, showing a significant improvement compared to analysis using either isotropic and axially symmetric tensors. This analysis indicates that the molecule undergoes significant anisotropic reorientation with a diffusion tensor having principal components {1.37 ± 0.05, 1.68 ± 0.06, 2.13 ± 0.07} × 107 s-1. Hydrodynamic calculations performed on the crystal structure predict values of {1.400, 1.45, 2.12 } × 107 s-1 when a solvent shell of 3.0 A is included in the calculation. Comparison of the principal axes with the symmetry axes of the dimeric structure derive...