title: Probing Asymmetric Charge Partitioning of Protein Oligomers during Tandem Mass Spectrometry.
abstract: Dissociation of gaseous protein complexes produced by native electrospray often induces an asymmetric partitioning of charge between ejected subunits. We present a simple asymmetric charge partitioning factor (ACPF) to quantify the magnitude of asymmetry in this effect. When applied to monomer ejection from the cytochrome c dimer and β-amylase tetramer, we found that the ~60-70% of precursor charge ending up in the ejected monomers corresponds to ACPFs of 1.38 and 2.51, respectively. Further, we used site-specific fragmentation from electron transfer dissociation (ETD) to identify differences in fragmentation and characterize domains of secondary-structure present in the dimer, ejected monomers, and monomers obtained directly from electrospray ionization (ESI). We found evidence of structural changes between the dimer and ejected monomer, but also that the ejected monomer had a nearly identical set of fragment ions produced by ETD as the ESI monomer with the same charge state. Surprisingly, APCF values for ETD fragment ions generated directly from the dimer revealed that the fragments undergo asymmetric charge partitioning at over twice the magnitude of that observed for ejection of the monomer.
authors.affiliation: Departments of Chemistry and Molecular Biosciences and the Proteomics Center of Excellence, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Philip D
authors.initials: PD
authors.lastname: Compton
authors.affiliation: Departments of Chemistry and Molecular Biosciences and the Proteomics Center of Excellence, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Luca
authors.initials: L
authors.lastname: Fornelli
authors.affiliation: Departments of Chemistry and Molecular Biosciences and the Proteomics Center of Excellence, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Neil L
authors.initials: NL
authors.lastname: Kelleher
authors.affiliation: Departments of Chemistry and Molecular Biosciences and the Proteomics Center of Excellence, Northwestern University, Evanston, Illinois 60208, USA.
authors.forename: Owen S
authors.initials: OS
authors.lastname: Skinner
keywords: asymmetric charge partitioning; electron transfer dissociation; protein complexes; proteomics