Trapped Ion Mobility Spectrometry of Native Macromolecular Assemblies

The structural elucidation of native macromolecular assemblies has been a subject of considerable interest in native mass spectrometry (MS), and more recently in tandem with ion mobility spectrometry (IMS-MS), for a better understanding of their biochemical and biophysical functions. In the present work, we describe a new generation trapped ion mobility spectrometer (TIMS), with extended mobility range (K0 = 0.185–1.84 cm2·V–1·s–1), capable of trapping high-molecular-weight (MW) macromolecular assemblies. This compact 4 cm long TIMS analyzer utilizes a convex electrode, quadrupolar geometry with increased pseudopotential penetration in the radial dimension, extending the mobility trapping to high-MW species under native state (i.e., lower charge states). The TIMS capabilities to perform variable scan rate (Sr) mobility measurements over short time (100–500 ms), high-mobility resolution, and ion-neutral collision cross-section (CCSN2) measurements are presented. The trapping capabilities of the convex electrode TIMS geometry and ease of operation over a wide gas flow, rf range, and electric field trapping range are illustrated for the first time using a comprehensive list of standards varying from CsI clusters (n = 6–73), Tuning Mix oligomers (n = 1–5), common proteins (e.g., ubiquitin, cytochrome C, lysozyme, concanavalin (n = 1–4), carbonic anhydrase, β clamp (n = 1–4), topoisomerase IB, bovine serum albumin (n = 1–3), topoisomerase IA, alcohol dehydrogenase), IgG antibody (e.g., avastin), protein–DNA complexes, and macromolecular assemblies (e.g., GroEL and RNA polymerase (n = 1–2)) covering a wide mass (up to m/z 19 000) and CCS range (up to 22 000 Å2 with <0.6% relative standard deviation (RSD)).