title: Metal-ion-specific screening of charge effects in protein amide H/D exchange and the Hofmeister series.
abstract: In this study, protein charge ladders and mass spectrometry were used to quantify how metal cations in the Hofmeister series (Na(+), K(+), Li(+), Mg(2+), and Ca(2+)) permute the effects of lysine acetylation on the rate of amide H/D exchange in a representative protein (myoglobin, Mb). The successive acetylation of up to 18 Lys-ε-NH3(+) groups in Mb caused a linear decrease in its global rate of amide H/D exchange (as measured by mass spectrometry), despite also decreasing the thermostability of Mb by >10 °C. The ability of a metal cation to screen kinetic electrostatic effects during H/D exchange-and to abolish the protective effect of acetylation against H/D exchange-was found to depend on the position of the cation in the Hofmeister series. Na(+) and K(+) cations did not fully equalize the rates of H/D exchange among each "rung" of the charge ladder, whereas Mg(2+) and Ca(2+) did equalize rates without eliminating the hydrophobic core of the protein (i.e., without unfolding Mb); Li(+) exhibited intermediate effects. The ability of Mg(2+) and Ca(2+) to completely screen electrostatic effects associated with the H/D exchange of charge isomers of Mb suggests that Mg(2+) or Ca(2+) (but not Na(+) or K(+)) can be used to quantify the magnitude by which electrostatic charge contributes to the observed rates of amide H/D exchange in proteins.
authors.affiliation: Department of Chemistry and Biochemistry, Baylor University , Waco, Texas 76706, United States.
authors.forename: Alireza
authors.initials: A
authors.lastname: Abdolvahabi
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Gober
authors.forename: Richard A
authors.initials: RA
authors.lastname: Mowery
authors.forename: Yunhua
authors.initials: Y
authors.lastname: Shi
authors.forename: Bryan F
authors.initials: BF
authors.lastname: Shaw
mesh_terms: D000577:Amides / Q000737:chemistry*; D002623:Chemistry Techniques, Analytical / Q000379:methods*; D003903:Deuterium / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D007477:Ions / Q000032:analysis*; D008673:Metals, Alkaline Earth / Q000032:analysis* / Q000737:chemistry; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry*
chemical_list: D000577:Amides; D007477:Ions; D008673:Metals, Alkaline Earth; D009211:Myoglobin; D006859:Hydrogen; D003903:Deuterium