title: Direct ionization of large proteins and protein complexes by desorption electrospray ionization-mass spectrometry.
abstract: Desorption electrospray ionization-mass spectrometry (DESI-MS) has advantages for rapid sample analysis with little or no sample pretreatment, but performance for large biomolecules has not been demonstrated. In this study, liquid sample DESI, an extended version of DESI used for analysis of liquid samples, was shown to have capabilities for direct ionization of large noncovalent protein complexes (>45 kDa) and proteins (up to 150 kDa). Protein complex ions (e.g., superoxide dismutase, enolase, and hemoglobin) desorbed from solution by liquid sample DESI were measured intact, indicating the capability of DESI for preserving weak noncovalent interactions. Doping the DESI spray solvent with supercharging reagents resulted in protein complex ions having increased multiple charging without complex dissociation. Ion mobility measurements of model protein cytochrome c showed that the supercharging reagent favored the more compact conformation for the lower charged protein ions. Liquid sample DESI of hydrophobic peptide gramicidin D suggests that the ionization mechanism involves a droplet pick-up mixing process. Measurement of liquid samples significantly extends the mass range of DESI-MS, allowing the analysis of high-mass proteins such as 150 kDa immunoglobulin G (IgG) and thus represents the largest protein successfully ionized by DESI to date.
authors.affiliation: Department of Chemistry and Biochemistry, David Geffen School of Medicine, University of California-Los Angeles, Los Angeles, California 90095, USA.
authors.forename: Carly N
authors.initials: CN
authors.lastname: Ferguson
authors.forename: Sabrina A
authors.initials: SA
authors.lastname: Benchaar
authors.forename: Zhixin
authors.initials: Z
authors.lastname: Miao
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Loo
authors.forename: Hao
authors.initials: H
authors.lastname: Chen
mesh_terms: D045304:Cytochromes c / Q000737:chemistry; D006096:Gramicidin / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry; D007074:Immunoglobulin G / Q000737:chemistry; D010751:Phosphopyruvate Hydratase / Q000737:chemistry; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013482:Superoxide Dismutase / Q000737:chemistry
chemical_list: D006454:Hemoglobins; D007074:Immunoglobulin G; D011506:Proteins; D006096:Gramicidin; D045304:Cytochromes c; D013482:Superoxide Dismutase; D010751:Phosphopyruvate Hydratase