title: Critical examination of gas-phase protein conformation/multimer ion formation by electrospray ion mobility-mass spectrometry.
abstract: The generally accepted view of protein structure in the gas-phase is that protein ions produced by electrospray ionization (ESI) exist in a number of different states, and the resulting charge state distribution (CSD) and ion mobility spectrum is interpreted as evidence for protein ions retaining some memory of solution-phase conformation. Even with the inclusion of ion mobility information, reports of protein ion structure in the gas-phase are oftentimes in disagreement not only within the discipline but also as interpreted by other gas-phase techniques. The focus of this work will be to correctly distinguish truly different ion conformations formed by ESI versus homomultimeric complexes with the same m/z. The concentration of cytochrome c in solution was varied over a wide range, and the multiply charged multimers (MCMs) present in the ion mobility/mass spectrum were unambiguously assigned by m/z selection and dissociation prior to ion mobility/mass spectrometry analysis. The results revealed false negatives for protein oligomer formation and false positives for protein conformational states and no evidence that gas-phase cytochrome c ions retain memory of solution-phase conformation, characteristics of great importance for structural biology. The results also suggest that the total IM-MS distribution for a protein is the complex result of individual MCMs either surviving until detection (undissociated) or dissociating into lower order multimers or a number of product ions for each m/z.
authors.affiliation: Genomics Research Center, Academia Sinica, 128 Academia Road, Nankang Sec. 2, Taipei 115, Taiwan.
authors.forename: Kent J
authors.initials: KJ
authors.lastname: Gillig
authors.forename: Chung-Hsuan
authors.initials: CH
authors.lastname: Chen
mesh_terms: D045304:Cytochromes c / Q000032:analysis*; D005740:Gases / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D020836:Protein Structure, Quaternary; D012996:Solutions / Q000737:chemistry; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D005740:Gases; D007477:Ions; D012996:Solutions; D045304:Cytochromes c