In article <Pine.SGI.3.91.950126174410.2174A-100000 at helix.nih.gov>, Mohan
Srinivasan <smohan at helix.nih.gov> wrote:
> Can proteins fold in a different way in the absence of
> gravity ?
The conformational free energy of a protein is primarily determined by
electrostatic forces and entropy. These forces, on a molecular scale are
_many_ orders of magnitude larger than the gravitational forces involved.
Even more important, the possible perturbations due to gravitation are
again _many_ orders of magnitude smaller than thermal perturbations under
physiological conditions. We do not expect gravity to have noticable
effetcs on protein folding.
Even more so, since external applied fields homogeneously affect all atoms
in the molecule, there is no gradient which might generate a force.
On the other hand, gravity can affect protein concentration. Concentration
affects the propensity towards aggregation and this influences unproductive
side-reactions along the folding pathway. This is a question of kinetics,
not thermodynamics.
Protein crystallization has _many_ variables. The presence or absence of
gravitational fields is one of them. It has been argued, that under
microgravitational conditions, the absence of convective currents in the
crystalization experiment should produce better crystals. Indeed,
space-shuttle experiments have grown crystals, that are no worse than those
which have been grown on earth ;-). But the reverse also works. A
BioTechnology cover page some years ago showed crystals grown in the
centrifuge, apparently high-G conditions favored nucleation under certain
conditions.
Greetings
--
Boris <steipe at lmb.uni-muenchen.de>
