  The asymmetry in the shapes of folded and unfolded states are probed using
two parameters, one being a measure of the sphericity and the other that
describes the shape. For the folded states, whose interiors are densely packed,
the radii of gyration (Rg) and these two parameters are calculated using the
coordinates of the experimentally determined structures. Although Rg scales as
expected for maximally compact structures, the distributions of the shape
parameters show that there is considerable asymmetry in the shapes of folded
structures. The degree of asymmetry is greater for proteins that form
oligomers. Analysis of the two- and three-body contacts in the native
structures shows that the presence of near equal number of contacts between
backbone and side-chains and between side-chains gives rise to dense packing.
We suggest that proteins with relatively large values of shape parameters can
tolerate volume mutations without greatly affecting the network of contacts or
their stability. To probe shape characteristics of denatured states we have
developed a model of a WW-like domain. The shape parameters, which are
calculated using Langevin simulations, change dramatically in the course of
coil to globule transition. Comparison of the values of shape parameters
between the globular state and the folded state of WW domain shows that both
energetic (especially dispersion in the hydrophobic interactions) and steric
effects are important in determining packing in proteins.
