LONG-RANGE MOTIONAL RESTRICTIONS IN A MULTIDOMAIN ZINC-FINGER PROTEINFROM ANISOTROPIC TUMBLING

Structural characterization of biomolecules in solution by nuclear mag netic resonance (NMR) spectroscopy is based primarily on the use of in terproton distances derived from homonuclear cross-relaxation experime nts. Information about short time-scale dynamics, on the other hand, i s obtained from relaxation rates of heteronuclear spin pairs such as ( N-1H)-N-15. By combining the two types of data and utilizing the depen dence of heteronuclear NMR relaxation rates on anisotropic diffusional rotational tumbling, it is possible to obtain structural information about long-range motional correlations between protein domains. This a pproach was applied to characterize the relative orientations and mobi lities of the first three zinc-finger domains of the Xenopus transcrip tion factor TFIIIA in aqueous solution. The data indicate that the mot ions of the individual zinc-finger domains are highly correlated on ti me scales shorter than 10 nanoseconds and that the average conformatio n of the three-finger polypeptide is elongated.