VERIFICATION OF PROTEIN STRUCTURES - SIDE-CHAIN PLANARITY

Nine of the 20 natural amino acids contain a planar group in their sid e chains. For these groups, normal deviations from planarity were deri ved by the study of similar fragments in accurately determined small-m olecule structures. Comparison of these deviations with values found f rom a representative set of high-quality protein structures revealed t hat the planarity of the aromatic residues and arginine in protein str uctures is comparable to similar fragments in small molecules. For Asn , Gin, Asp and Glu, however, the deviations are up to twice as large a s in comparable small-molecule structures, suggesting that adding an e xtra planarity restraint for these residue types could improve refinem ent procedures.