title: Top-down MALDI-in-source decay-FTICR mass spectrometry of isotopically resolved proteins.
abstract: An accurate mass measurement of a known protein provides information on potential amino acid deletions and post-translational modifications. Although this field is dominated by strategies based on electrospray ionization, mass spectrometry (MS) methods using matrix-assisted laser desorption/ionization (MALDI) have the advantage of yielding predominantly singly charged precursor ions, thus avoiding peak overlap from different charge states of multiple species. Such MALDI-MS methods require mass measurement at ultrahigh resolution, which is provided by Fourier transform ion cyclotron resonance (FTICR) mass analyzers. Recently, using a MALDI-FTICR-MS platform equipped with a 15 T magnet, we reported on the mass analysis of intact human serum peptides and small proteins with isotopic resolution up to ∼15 kDa and identified new proteoforms from an accurate measurement of mass distances. In the current study, we have used this FTICR system after an upgrade with a novel dynamically harmonized ICR cell, i.e., ParaCell, for mapping isotopically resolved intact proteins up to about 17 kDa and performed top-down MALDI in-source decay (ISD) analysis. Standard proteins myoglobin (m/z-value 16,950) and ribonuclease B (m/z-value 14,900) were measured with resolving powers of 62,000 and 61,000, respectively. Furthermore, it will be shown that (singly charged) MALDI-ISD fragment ions can be measured at isotopic resolution up to m/z-value 12,000 (e.g., resolving power 39,000 at m/z-value 12,000) providing more reliable identifications. Moreover, examples are presented of pseudo-MS(3) experiments on ISD fragment ions from RNase B by collisional-induced dissociation (CID).
authors.affiliation: Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC, Leiden, The Netherlands.
authors.forename: Simone
authors.initials: S
authors.lastname: Nicolardi
authors.affiliation: Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC, Leiden, The Netherlands.
authors.forename: Linda
authors.initials: L
authors.lastname: Switzar
authors.affiliation: Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC, Leiden, The Netherlands.
authors.forename: André M
authors.initials: AM
authors.lastname: Deelder
authors.affiliation: Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC, Leiden, The Netherlands.
authors.forename: Magnus
authors.initials: M
authors.lastname: Palmblad
authors.affiliation: Center for Proteomics and Metabolomics, Leiden University Medical Center (LUMC), PO Box 9600, 2300 RC, Leiden, The Netherlands.
authors.forename: Yuri E M
authors.initials: YE
authors.lastname: van der Burgt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D017357:Cyclotrons; D005583:Fourier Analysis; D007554:Isotopes; D008969:Molecular Sequence Data; D009211:Myoglobin / Q000737:chemistry*; D012260:Ribonucleases / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000295:instrumentation / Q000379:methods*
chemical_list: D007554:Isotopes; D009211:Myoglobin; D012260:Ribonucleases; C029600:ribonuclease B