Journal
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
Volume 29, Issue 1, Pages 183-193Publisher
SPRINGER
DOI: 10.1007/s13361-017-1799-4
Keywords
Native-mass spectrometry; Membrane protein; Fourier transform ion cyclotron resonance
Funding
- US National Institutes of Health [R01GM103479, S10RR028893]
- US Department of Energy (UCLA/DOE Institute for Genomics and Proteomics) [DE-FC03-02ER63421]
- Amgen, Inc.
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Membrane protein characterization is consistently hampered by challenges with expression, purification, and solubilization. Among several biophysical techniques employed for their characterization, native-mass spectrometry (MS) has emerged as a powerful tool for the analysis of membrane proteins and complexes. Here, two MS platforms, the FT-ICR and Q-ToF, have been explored to analyze the homotetrameric water channel protein, AquaporinZ (AqpZ), under non-denaturing conditions. This 97 kDa membrane protein complex can be readily liberated from the octylglucoside (OG) detergent micelle under a range of instrument conditions on both MS platforms. Increasing the applied collision energy of the FT-ICR collision cell yielded varying degrees of tetramer (97 kDa) liberation from the OG micelles, as well as dissociation into the trimeric (72 kDa) and monomeric (24 kDa) substituents. Tandem-MS on the Q-ToF yielded higher intensity tetramer signal and, depending on the m/z region selected, the observed monomer signal varied in intensity. Precursor ion selection of an m/z range above the expected protein signal distribution, followed by mild collisional activation, is able to efficiently liberate AqpZ with a high S/N ratio. The tetrameric charge state distribution obtained on both instruments demonstrated superpositioning of multiple proteoforms due to varying degrees of N-terminal formylation.
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