The determinants of carboxyl pKa values in turkey ovomucoid third domain.
A computational methodology for protein pK(a) predictions, based on ab initio quantum mechanical treatment of part of the protein and linear Poisson-Boltzmann equation treatment of the bulk solvent, is presented. The method is used to predict and interpret the pK(a) values of the five carboxyl residues (Asp7, Glu10, Glu19, Asp27, and Glu43) in the serine protease inhibitor turkey ovomucoid third domain. All the predicted pK(a) values are within 0.5 pH units of experiment, with a root-mean-square deviation of 0.31 pH units. We show that the decreased pK(a) values observed for some of the residues are primarily due to hydrogen bonds to the carboxyl oxygens. Hydrogen bonds involving amide protons are shown to be particularly important, and the effect of hydrogen bonding is shown to be nonadditive. Hydrophobic effects are also shown to be important in raising the pK(a). Interactions with charged residues are shown to have relatively little effect on the carboxyl pK(a) values in this protein, in general agreement with experiment.
Li
Hui
H
Department of Chemistry, The University of Iowa, Iowa City 52242, USA.
Robertson
Andrew D
AD
Jensen
Jan H
JH
D000818:Animals; D001224:Aspartic Acid / Q000737:chemistry*; D019295:Computational Biology / Q000379:methods*; D018698:Glutamic Acid / Q000737:chemistry*; D006860:Hydrogen Bonding; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D015394:Molecular Structure; D010059:Ovomucin / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D014422:Turkeys
D001224:Aspartic Acid; D010059:Ovomucin; D018698:Glutamic Acid