title: pH-dependent random coil (1)H, (13)C, and (15)N chemical shifts of the ionizable amino acids: a guide for protein pK a measurements.
abstract: The pK a values and charge states of ionizable residues in polypeptides and proteins are frequently determined via NMR-monitored pH titrations. To aid the interpretation of the resulting titration data, we have measured the pH-dependent chemical shifts of nearly all the (1)H, (13)C, and (15)N nuclei in the seven common ionizable amino acids (X = Asp, Glu, His, Cys, Tyr, Lys, and Arg) within the context of a blocked tripeptide, acetyl-Gly-X-Gly-amide. Alanine amide and N-acetyl alanine were used as models of the N- and C-termini, respectively. Together, this study provides an essentially complete set of pH-dependent intra-residue and nearest-neighbor reference chemical shifts to help guide protein pK a measurements. These data should also facilitate pH-dependent corrections in algorithms used to predict the chemical shifts of random coil polypeptides. In parallel, deuterium isotope shifts for the side chain (15)N nuclei of His, Lys, and Arg in their positively-charged and neutral states were also measured. Along with previously published results for Asp, Glu, Cys, and Tyr, these deuterium isotope shifts can provide complementary experimental evidence for defining the ionization states of protein residues.
authors.affiliation: Department of Biochemistry and Molecular Biology, Life Sciences Centre, 2350 Health Sciences Mall, University of British Columbia, Vancouver, BC, V6T 1Z3, Canada.
authors.forename: Gerald
authors.initials: G
authors.lastname: Platzer
authors.forename: Mark
authors.initials: M
authors.lastname: Okon
authors.forename: Lawrence P
authors.initials: LP
authors.lastname: McIntosh
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D002247:Carbon Isotopes; D002264:Carboxylic Acids / Q000737:chemistry; D003903:Deuterium; D006859:Hydrogen / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009587:Nitrogen Isotopes; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D011506:Proteins / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D002247:Carbon Isotopes; D002264:Carboxylic Acids; D009587:Nitrogen Isotopes; D011506:Proteins; D006859:Hydrogen; D003903:Deuterium