Characterization of the dynamic properties of Rhodobacter capsulatus ferricytochrome c'--a 28 kDa paramagnetic heme protein.

The cytochrome c' are paramagnetic heme proteins generally consisting of two identical 14 kDa subunits. The recent assignment of the 1H and 15N resonances of the Rhodobacter capsulatus ferricytochrome c' has allowed characterization of the dynamic properties by measurement of the heteronuclear NOE for each resolved amide group. The relative importance of fast local motion and paramagnetic effect on nuclear relaxation were distinguished by comparison of the measured heteronuclear NOE with that of the overall experimental average. We show that the average experimental value of -0.16 corresponds to the rigid body motion expected for a spherical complex of 28 kDa. Residues 3-5, 50-55 and 69-70 exhibit decreased heteronuclear NOE due to local motions on a fast time scale with respect to molecular tumbling. Based on the X-ray crystal structure of the homologous cytochrome c' from Chromatium vinosum, the mobile regions correspond to the N-terminus of helix-1 and 2 regions of nonregular secondary structure located between helices-2 and -3.