title: Quantum chemistry can locally improve protein crystal structures.
abstract: We have re-refined the X-ray structure of the heme site in cytochrome c553, supplementing the crystallographic data with quantum chemical geometry optimizations, instead of the molecular mechanics force field used in standard crystallographic refinement. By comparing the resulting structure, obtained using medium-resolution data (170 pm), with an atomic-resolution structure (95 pm) of the same protein, we show that the inclusion of quantum chemical information into the refinement procedure improves the structure significantly. Thus, errors in the Fe-ligand distances are reduced from 3 to 32 pm in the low-resolution structure to 0-5 pm in the re-refined structure, one side-chain atom changes its conformation (a movement by 214 pm toward its position in the high-resolution structure), and the R factors are improved by up to 0.018. Thus, quantum refinement may be a powerful method to obtain an accurate structure for interesting parts of a protein.
authors: Department of Theoretical Chemistry, Lund University, Chemical Center, P.O. Box 124, S-221 00 Lund, Sweden. Ulf.Ryde@teokem.lu.se
authors: Ulf
authors: U
authors: Ryde
authors: Kristina
authors: K
authors: Nilsson
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D003574:Cytochrome c Group / Q000737:chemistry; D011506:Proteins / Q000737:chemistry*; D011789:Quantum Theory; D012984:Software; D013816:Thermodynamics
chemical_list: D003574:Cytochrome c Group; D011506:Proteins; C083951:cytochrome c553