Prediction of protein side-chain conformations by principal component analysis for fixed main-chain atoms

Abstract

A method of side-chain prediction without calculating the potential function is introduced. It is based on the assumption that similar side-chain conformations have a similar structural environment around the side chains. The environment information is represented by vectors that were obtained from principle component analysis and represented by the variance of positions of main-chain atoms around side chains. This information was added to the side-chain library (rotamer library) made from X-ray structures. Side-chain conformations were constructed using this side-chain library without using potential functions. An optimal solution was determined by comparing environmental information with the backbone conformation around the side chain to be predicted and native ones in the library. The method was performed for 15 proteins whose structures were known. The result for the root-mean-square deviation between the predicted and X-ray side-chain conformations was ~1.5 Å (the value for core residues was ~1.1 Å) and the percentage of predicted χ1 angles correct within 40°was ~65% (75% for the core). The computational time was short (~60 s for the prediction of proteins with 200 amino acid residues). About 70% of the side-chain conformations were constructed by location of the main-chain atoms around the central C(β) atom and the average of r.m.s.d. was ~1.4 Å (for core residues the average was ~1.0 Å).