Several computational models describe rotational tumbling and rotational relaxation time when describing protein motion and dynamics. What is meant by relaxation time and how is related tumbling? Furthermore, what significance does it have on interaction kinetics say like polymerization reaction.
Protein NMR signals are affected by tumbling motions of proteins, which interfere with the alignment of nuclear spin with the external magnetic field. This allows to experimentally measure rational motions of a protein as a function of solvent viscosity
see e.g. Determination of protein rotational correlation time from NMR relaxation data at various solvent viscosities.
Protein NMR signals are affected by tumbling motions of proteins, which interfere with the alignment of nuclear spin with the external magnetic field. This allows to experimentally measure rational motions of a protein as a function of solvent viscosity
see e.g. Determination of protein rotational correlation time from NMR relaxation data at various solvent viscosities.
Rotation and tumbling describe movements around the three principal axes of a protein structure. As a general model, which is fairly coarse but often sufficient, you can assume that proteins (single domains at least) take three general shapes: spheric, oblong and oblate. There are three possible rotations, X, Y and Z, which when combined describe the overall rotational motions. With respect to intermolecular interactions the correlation times (time it takes to rotate Q degrees in time T) can have an influence on the possibility of those to form. In enzymatic, which generally occur on a fast timescale, the correlation time might influence substrate turnover. I am not an expert on polymerization, but I would assume it might have a negligible influence, since correlation times of the fast growing polymer will become exceedingly long quickly.
With respect to relaxation times, Annemarie Honegger already mentioned their roles in NMR. The nuclear spin relaxes faster if aligned longer to the external magnetic field. As a general rule, the smaller the molecule the faster the correlation time and the slower the relaxation time. Relaxation time are directly connected to the ability to recored a meaningful signal.
It means what it says, that in addition to translational motion in 3D, a protein, or any body, can rotate around its centre of gravity (CoG) and the angular displacements are quantified in relation to the three azimuthal angles. These are usually defined by the three orthogonal components of the inertial moments for that body. (Tumbling can also be described as a rotation about a point other than the CoG, but this rotation can always be partitioned into two components - a translational motion and a CoG-centred rotation).
In an NMR experiment, Annemarie's explanation is correct.
Inside cells, proteins do not tumble about much, or not at all really, they are usually integrated into semirigid intracellular structures (other proteins mostly). In the membrane they can "surf" about a bit in the 2D environment of the membrane, but there is a lot of integration into complexes there also. Outside the cell, if the protein finds itself free to move in extracellular fluid then there can be tumbling and indeed that might in some cases be a necessary part of their mechanism of action.
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