Evaluation of Protein Docking Predictions Using Hex 3.1 in CAPRI Rounds 1–2

This article describes and reviews our efforts using Hex 3.1 to predict the docking modes of the seven target protein-protein complexes presented in the CAPRI (Critical Assessment of Predicted Interactions) blind docking trial. For each target, the structure of at least one of the docking partners was given in its unbound form, and several of the targets involved large multimeric structures (e.g. Lactobacillus HPr kinase, hemagglutinin, bovine rotavirus VP6). Here, we describe several enhancements to our original spherical polar Fourier docking correlation algorithm. For example, a novel surface sphere smothering algorithm is introduced to generate multiple local coordinate systems around the surface of a large receptor molecule which may be used to define a small number of initial ligand docking orientations distributed over the receptor surface. High resolution spherical polar docking correlations are performed over the resulting receptor surface patches, and candidate docking solutions are refined using a novel soft molecular mechanics energy minimisation procedure. Overall, this approach identified two good solutions at rank 5 or less for two of the seven CAPRI complexes. Subsequent analysis of our results shows that Hex 3.1 is able to place good solutions within a list of 20 or less for four of the seven targets. This demonstrates that useful in silico protein-protein docking predictions can now be made with increasing confidence, even for very large macromolecular complexes.