Journal
JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY
Volume 27, Issue 1, Pages 31-40Publisher
SPRINGER
DOI: 10.1007/s13361-015-1244-5
Keywords
Protein structure; Gas phase ion; Electrospray; Collision cross section; Protein unfolding
Funding
- Natural Sciences and Engineering Research Council of Canada (NSERC)
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The question whether electrosprayed protein ions retain solution-like conformations continues to be a matter of debate. One way to address this issue involves comparisons of collision cross sections (Omega) measured by ion mobility spectrometry (IMS) with Omega values calculated for candidate structures. Many investigations in this area employ traveling wave IMS (TWIMS). It is often implied that nanoESI is more conducive for the retention of solution structure than regular ESI. Focusing on ubiquitin, cytochrome c, myoglobin, and hemoglobin, we demonstrate that Omega values and collisional unfolding profiles are virtually indistinguishable under both conditions. These findings suggest that gas-phase structures and ion internal energies are independent of the type of electrospray source. We also note that TWIMS calibration can be challenging because differences in the extent of collisional activation relative to drift tube reference data may lead to ambiguous peak assignments. It is demonstrated that this problem can be circumvented by employing collisionally heated calibrant ions. Overall, our data are consistent with the view that exposure of native proteins to electrospray conditions can generate kinetically trapped ions that retain solution-like structures on the millisecond time scale of TWIMS experiments.
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