title: Numerical calculations of the pH of maximal protein stability. The effect of the sequence composition and three-dimensional structure.
abstract: A large number of proteins, found experimentally to have different optimum pH of maximal stability, were studied to reveal the basic principles of their preference for a particular pH. The pH-dependent free energy of folding was modeled numerically as a function of pH as well as the net charge of the protein. The optimum pH was determined in the numerical calculations as the pH of the minimum free energy of folding. The experimental data for the pH of maximal stability (experimental optimum pH) was reproducible (rmsd = 0.73). It was shown that the optimum pH results from two factors - amino acid composition and the organization of the titratable groups with the 3D structure. It was demonstrated that the optimum pH and isoelectric point could be quite different. In many cases, the optimum pH was found at a pH corresponding to a large net charge of the protein. At the same time, there was a tendency for proteins having acidic optimum pHs to have a base/acid ratio smaller than one and vice versa. The correlation between the optimum pH and base/acid ratio is significant if only buried groups are taken into account. It was shown that a protein that provides a favorable electrostatic environment for acids and disfavors the bases tends to have high optimum pH and vice versa.
authors.affiliation: Howard Hughes Medical Institute and Columbia University, Biochemistry Department, New York 10032, USA. ea388@columbia.edu
authors.forename: Emil
authors.initials: E
authors.lastname: Alexov
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry; D000595:Amino Acid Sequence; D002401:Cathepsin B / Q000737:chemistry / Q000378:metabolism; D004795:Enzyme Stability; D004798:Enzymes / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D011506:Proteins / Q000737:chemistry*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013816:Thermodynamics; D000516:alpha-Amylases / Q000737:chemistry
chemical_list: D004798:Enzymes; D011506:Proteins; D000516:alpha-Amylases; D002401:Cathepsin B; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase