title: Calculation of protein ionization equilibria with conformational sampling: pK(a) of a model leucine zipper, GCN4 and barnase.
abstract: The use of conformational ensembles provided by nuclear magnetic resonance (NMR) experiments or generated by molecular dynamics (MD) simulations has been regarded as a useful approach to account for protein motions in the context of pK(a) calculations, yet the idea has been tested occasionally. This is the first report of systematic comparison of pK(a) estimates computed from long multiple MD simulations and NMR ensembles. As model systems, a synthetic leucine zipper, the naturally occurring coiled coil GCN4, and barnase were used. A variety of conformational averaging and titration curve-averaging techniques, or combination thereof, was adopted and/or modified to investigate the effect of extensive global conformational sampling on the accuracy of pK(a) calculations. Clustering of coordinates is proposed as an approach to reduce the vast diversity of MD ensembles to a few structures representative of the average electrostatic properties of the system in solution. Remarkable improvement of the accuracy of pK(a) predictions was achieved by the use of multiple MD simulations. By using multiple trajectories the absolute error in pK(a) predictions for the model leucine zipper was reduced to as low as approximately 0.25 pK(a) units. The validity, advantages, and limitations of explicit conformational sampling by MD, compared with the use of an average structure and a high internal protein dielectric value as means to improve the accuracy of pK(a) calculations, are discussed.
authors.affiliation: Department of Biochemistry, University of Zurich, Zurich, Switzerland.
authors.forename: Alemayehu A
authors.initials: AA
authors.lastname: Gorfe
authors.forename: Philippe
authors.initials: P
authors.lastname: Ferrara
authors.forename: Amedeo
authors.initials: A
authors.lastname: Caflisch
authors.forename: Daniel N
authors.initials: DN
authors.lastname: Marti
authors.forename: Hans Rudolf
authors.initials: HR
authors.lastname: Bosshard
authors.forename: Ilian
authors.initials: I
authors.lastname: Jelesarov
mesh_terms: D001426:Bacterial Proteins; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins; D004563:Electrochemistry; D005656:Fungal Proteins / Q000737:chemistry*; D016350:Leucine Zippers; D008279:Magnetic Resonance Imaging; D018583:Pliability; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry*; D012260:Ribonucleases / Q000737:chemistry*; D029701:Saccharomyces cerevisiae Proteins
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D029701:Saccharomyces cerevisiae Proteins; D011494:Protein Kinases; D012260:Ribonucleases; C019760:Bacillus amyloliquefaciens ribonuclease