Kinetic intermediates of holo- and apo-myoglobin studied using HDX-TIMS-MS and molecular dynamic simulations

J Am Soc Mass Spectrom. 2015 Apr;26(4):555-63. doi: 10.1007/s13361-014-1067-9. Epub 2015 Feb 18.


In the present work, the kinetic intermediates of holo- and apo-myoglobin were studied by correlating the ion-neutral collision cross section and time resolved H/D back exchange rate simultaneously in a trapped ion mobility spectrometer coupled to a mass spectrometer (HDX-TIMS-MS). The high mobility resolution of the TIMS cell permitted the observation of multiple IMS bands and complementary molecular dynamics simulations resulted in the assignment of candidate structures for each experimental condition studied (e.g., holo [M + 8H](+8)-[M + 9H](+9) and apo [M + 9H](+9)-[M + 19H](+19)). Inspection of the kinetic intermediates suggests that the tertiary structure of apomyoglobin unfolds quickly upon the loss of the Fe protoporphyrin IX that stabilizes the interactions between the A, G, and H helices. In the absence of the porphyrin heme, the apomyoglobin unfolds to Xn kinetic intermediates that vary in the extent of unfolding as a result of the observed charge state.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoproteins / chemistry*
  • Apoproteins / metabolism*
  • Deuterium Exchange Measurement
  • Kinetics
  • Mass Spectrometry / methods*
  • Molecular Dynamics Simulation*
  • Myoglobin / chemistry*
  • Myoglobin / metabolism*


  • Apoproteins
  • Myoglobin
  • apomyoglobin