title: ff14SB: Improving the Accuracy of Protein Side Chain and Backbone Parameters from ff99SB.
abstract: Molecular mechanics is powerful for its speed in atomistic simulations, but an accurate force field is required. The Amber ff99SB force field improved protein secondary structure balance and dynamics from earlier force fields like ff99, but weaknesses in side chain rotamer and backbone secondary structure preferences have been identified. Here, we performed a complete refit of all amino acid side chain dihedral parameters, which had been carried over from ff94. The training set of conformations included multidimensional dihedral scans designed to improve transferability of the parameters. Improvement in all amino acids was obtained as compared to ff99SB. Parameters were also generated for alternate protonation states of ionizable side chains. Average errors in relative energies of pairs of conformations were under 1.0 kcal/mol as compared to QM, reduced 35% from ff99SB. We also took the opportunity to make empirical adjustments to the protein backbone dihedral parameters as compared to ff99SB. Multiple small adjustments of φ and ψ parameters were tested against NMR scalar coupling data and secondary structure content for short peptides. The best results were obtained from a physically motivated adjustment to the φ rotational profile that compensates for lack of ff99SB QM training data in the β-ppII transition region. Together, these backbone and side chain modifications (hereafter called ff14SB) not only better reproduced their benchmarks, but also improved secondary structure content in small peptides and reproduction of NMR χ1 scalar coupling measurements for proteins in solution. We also discuss the Amber ff12SB parameter set, a preliminary version of ff14SB that includes most of its improvements.
authors.affiliation: Graduate Program in Biochemistry and Structural Biology, ‡Department of Chemistry, and §Laufer Center for Physical and Quantitative Biology, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: James A
authors.initials: JA
authors.lastname: Maier
authors.affiliation: Graduate Program in Biochemistry and Structural Biology, ‡Department of Chemistry, and §Laufer Center for Physical and Quantitative Biology, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Carmenza
authors.initials: C
authors.lastname: Martinez
authors.affiliation: Graduate Program in Biochemistry and Structural Biology, ‡Department of Chemistry, and §Laufer Center for Physical and Quantitative Biology, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Koushik
authors.initials: K
authors.lastname: Kasavajhala
authors.affiliation: Graduate Program in Biochemistry and Structural Biology, ‡Department of Chemistry, and §Laufer Center for Physical and Quantitative Biology, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Lauren
authors.initials: L
authors.lastname: Wickstrom
authors.affiliation: Graduate Program in Biochemistry and Structural Biology, ‡Department of Chemistry, and §Laufer Center for Physical and Quantitative Biology, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Kevin E
authors.initials: KE
authors.lastname: Hauser
authors.affiliation: Graduate Program in Biochemistry and Structural Biology, ‡Department of Chemistry, and §Laufer Center for Physical and Quantitative Biology, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Carlos
authors.initials: C
authors.lastname: Simmerling
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D056004:Molecular Dynamics Simulation; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D011789:Quantum Theory; D013816:Thermodynamics
chemical_list: D000596:Amino Acids; D010455:Peptides; D011506:Proteins; C019529:polyalanine