Coordination geometry of nonbonded residues in globular proteins

Background: Two opposite Views have been advanced for the packing of sidechains in globular proteins. The first is the jigsaw puzzle model, in which the complementarity of size and shape is essential. The second, the nuts-and-bolts model, suggests that constraints induced by steric complementarity or pairwise specificity have little influence. Here, the angular distributions of sidechains around amino acids of different types are analyzed, in order to capture the preferred (if any) coordination loci in the neighborhood of a given type of amino acid.