title: Electrostatic effects on the folding stability of FKBP12.
abstract: The roles of electrostatic interactions in protein folding stability have been a matter of debate, largely due to the complexity in the theoretical treatment of these interactions. We have developed computational methods for calculating electrostatic effects on protein folding stability. To rigorously test and further refine these methods, here we carried out experimental studies into electrostatic effects on the folding stability of the human 12-kD FK506 binding protein (FKBP12). This protein has a close homologue, FKBP12.6, with amino acid substitutions in only 18 of their 107 residues. Of the 18 substitutions, 8 involve charged residues. Upon mutating FKBP12 residues at these 8 positions individually into the counterparts in FKBP12.6, the unfolding free energy (ΔGu) of FKBP12 changed by -0.3 to 0.7 kcal/mol. Accumulating stabilizing substitutions resulted in a mutant with a 0.9 kcal/mol increase in stability. Additional charge mutations were grafted from a thermophilic homologue, MtFKBP17, which aligns to FKBP12 with 31% sequence identity over 89 positions. Eleven such charge mutations were studied, with ΔΔGu varying from -2.9 to 0.1 kcal/mol. The predicted electrostatic effects by our computational methods with refinements herein had a root-mean-square deviation of 0.9 kcal/mol from the experimental ΔΔGu values on 16 single mutations of FKBP12. The difference in ΔΔGu between mutations grafted from FKBP12.6 and those from MtFKBP17 suggests that more distant homologues are less able to provide guidance for enhancing folding stability.
authors.affiliation: Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA.|Present address: Department of Chemistry and Physics, Bellarmine University, 2001 Newburg Road, Louisville, KY 40205, USA.
authors.forename: Jyotica
authors.initials: J
authors.lastname: Batra
authors.affiliation: Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA.|Present address: Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089, USA.
authors.forename: Harianto
authors.initials: H
authors.lastname: Tjong
authors.affiliation: Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA.
authors.forename: Huan-Xiang
authors.initials: HX
authors.lastname: Zhou
mesh_terms: D019943:Amino Acid Substitution; D006801:Humans; D009154:Mutation; D017510:Protein Folding; D055550:Protein Stability; D058767:Protein Unfolding; D055672:Static Electricity; D022061:Tacrolimus Binding Protein 1A / Q000737:chemistry* / Q000235:genetics; D013816:Thermodynamics
chemical_list: D022061:Tacrolimus Binding Protein 1A
keywords: charge mutations; electrostatic interactions; folding free energy