Two dimensional diffusion of small molecules on protein surfaces: an EPR study of the restricted translational diffusion of protein-bound spin labels.
Steinhoff HJ, Dombrowsky O, Karim C, Schneiderhahn C
Heisenberg spin exchange rates and dipole-dipole spin lattice relaxation
rates for deuterated 14N- and 15N-spin labels bound selectively to the
histidine His15 and to the lysines Lys13, 96, 97 of the lysozyme molecule
have been determined with the aid of electron spin resonance spectroscopy.
The results can be interpreted in terms of a two dimensional translational
diffusion of the nitroxide tips of the spin labels along the protein surface
within restricted surface areas. The spin labels are regarded as models
for long amino acid side chains and as probes for the dynamics of protein
and water in the vicinity of the protein surface. The translational diffusion
coefficient DII is reduced by a factor of between six and thirty compared
to the value of D found for the spin labels in bulk water, its value for
T=295 K is given by (1.3+or-0.6).10-10 m2 s-1>or=DII>or=(2.4+or-0.3).10-11