EASY ADAPTATION OF PROTEIN-STRUCTURE TO SEQUENCE

An investigation into the conservation of coarse, medium and fine grain structural properties has been performed over a data set of 175 protein tertiary structures in 34 different families, each characterized by a common core fold and a library of conserved sites formed for each family. It is shown that, while the conservation of coarse and medium grain properties correlates to the structural deviation between the proteins, fine grain properties are poorly conserved except in functional sites. This flexibility in fine grain properties suggests that folding can be viewed as an optimization process whereby side chains have freedom to position themselves as best as possible given environmental conformational constraints: and that given a basic framework, the local structure is able to adapt easily to sequence variation. The conserved cores of the 34 families are used to estimate a minimal core size of 35% of the fold, consistent with buried residue considerations. Finally, conservation in side chain (chi)1 torsion angles is combined with structural deviation, sequence deviation and resolution to suggest a set of example structure pairs suitable for testing automatic homology modelling programs.