Fundamental Sessions
Day 3, June 12（Fri.） 10:09-10:27 Room D (5F 511+512)
- 3D-O1-1009（2P-09）
High-Pressure Electrospray Ionization-Ion Mobility-Mass Spectrometry of Cytochrome c Under Strongly Acidic Conditions
(1Tohoku Univ., 2Hokkaido Univ. of Education Sapporo, 3Univ. Yamanashi)
oShunsuke Kamioka1, Keijiro Ohshimo2, Fuminori Misaizu1, Lee Chen3
A substantial increase in acidity is known to induce compaction of a fully unfolded protein into a compact molten globule, a phenomenon referred to as “acid-induced folding of proteins”. However, it is difficult to handle strong acid aqueous solutions using conventional electrospray ionization methods for mass spectrometry because of their high electrical conductivity and surface tension. Previously, high-pressure electrospray ionization (HP-ESI) was used to acquire well-resolved mass spectra of cytochrome c (cyt c) under these harsh conditions. Here, HP-ESI was combined with ion mobility-mass spectrometry (IM-MS), in which coexisting conformers with the same m/z are separated through collisions with a buffer gas, to obtain further structural information on acid-induced compaction of cyt c. We compared the conformational landscapes of the low charge state +6 ions in ammonium acetate (AA) at pH 7 (near-native condition) and in trifluoroacetic acid (TFA) at pH 1 (harsh condition). As a result, three conformational families were observed under both conditions, and the compact conformation was significantly more abundant in TFA at pH 1 than in AA at pH 7. These results demonstrate that cyt c adopts a highly compact conformation in strongly acidic solution at pH 1.