Rotational Diffusion Anisotropy 
In the major number of relaxation NMR studies, spherical globular proteins ans isotropic overall rotational diffusion is assumed. However, the distributions of orientations of N-H bond vectors are not isotropic in many proteins and, therefore, correlations between bond vector orientations reduce the accuracy and precision of diffusion tensors extracted from relaxation data. The determination of the rotational diffusion tensor is therefore a prerequisite in the analysis of internal dynamics using heteronuclear relaxation. Teh determination of the overall rotational diffusion tensor can also provide important information concerning the overall form of globular proteins, and the relative domainorientation in modular proteins.

Rotational diffusion anisotropies have been determined from:

  • Direct fitting of R2/R1 ratios for a series of nuclear spins ( 95JACS12562 , 95BIO5212 , 96BIO4867 , and 00JMR66-146 ). This parameter becomes independent of internal dynamics in the fast motion limit while remaining highly sensitive to overall diffusion. Programs for analyzing such results has been presented as, for instance, TENSOR ( 00JB23 ).

  • Analysis of local diffusion coefficients that are derived in turn from 15N relaxation rate constants ( 95SCI886 and 98JACS4889 ) and using combined 15N and 13C relaxation data ( 97JB287 and 01JMR204-149 ).
  • Joint fit of relaxation data acquired at several viscosities of a protein solution 04JB431-30 )
    • Some interesting studies:
  • About the precission on the characterization of anisotropic rotational diffusion from 15N relaxation data ( 99JACS4538 )
  • 15N relaxation data extracted from proteins showing anisotropic rotational diffusion has been used to propose a quality factor for protein structure validation ( 00JMR367-144 ).
  • Application: Measurement of diffusion anisotropy and comparison with dipolar coupling data ( 01JB83-20 ).
  • Analysis of the effects of rotational anisotropy on the model-free analysis of a ternary complex ( 01JB209-19 ).
  • A grahical method for the analysis of anisotropic rotational diffusion has been proposed ( 01JB181-19 ).
  • Characterization of the overall and local dynamics of a protein with intermediate rotational anisotropy (03JB261-27).