Metal-ion-specific screening of charge effects in protein amide H/D exchange and the Hofmeister series

Anal Chem. 2014 Oct 21;86(20):10303-10. doi: 10.1021/ac502714v. Epub 2014 Sep 29.


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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amides / chemistry*
  • Chemistry Techniques, Analytical / methods*
  • Deuterium / chemistry*
  • Hydrogen / chemistry*
  • Ions / analysis*
  • Metals, Alkaline Earth / analysis*
  • Metals, Alkaline Earth / chemistry
  • Models, Molecular
  • Myoglobin / chemistry*


  • Amides
  • Ions
  • Metals, Alkaline Earth
  • Myoglobin
  • Hydrogen
  • Deuterium