title: Ion coalescence in Fourier transform mass spectrometry: should we worry about this in shotgun proteomics?
abstract: Coupling of motion of the ion clouds with close m/z values is a well-established phenomenon for ion- trapping mass analyzers. In Fourier transform ion cyclotron resonance mass spectrometry it is known as ion coalescence. Recently, ion coalescence was demonstrated and semiquantitatively characterized for the Orbitrap mass analyzer as well. When it occurs, the coalescence negatively affects the basic characteristics of a mass analyzer. Specifically, the dynamic range available for the high resolving power mass measurements reduces. In shotgun proteomics, another potentially adverse effect of ion coalescence is interference of the isotopic envelopes for the coeluting precursor ions of close m/z values, subjected to isolation before fragmentation. In this work we characterize coalescence events for synthetic peptide mixtures with fully and partially overlapping (13)C-isotope envelopes including pairs of peptides with glutamine deamidation. Furthermore, we demonstrate that fragmentation of the otherwise coalesced peptide ion clouds may remove the locking between them owing to the total charge redistribution between more ion species in the mass spectrum. Finally, we estimated the possible scale of the coalescence phenomenon for shotgun proteomics by considering the fraction of coeluted peptide pairs with the close masses using literature data for the yeast proteome. It was found that up to one tenth of all peptide identifications with the relative mass differences of 20 ppm or less in the corresponding pairs may potentially experience the coalescence of the (13)C-isotopic envelopes. However, sample complexity in a real proteomics experiment and precursor ion signal splitting between many channels in tandem mass spectrometry drastically increase the threshold for coalescence, thus leading to practically coalescence-free proteomics based on Fourier transform mass spectrometry.
authors: V.L. Talrose Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences, 38 Leninsky Pr., Bld. 2, Moscow 119334, Russia. iatarasova@yandex.ru.
authors: Irina A
authors: IA
authors: Tarasova
authors: Institute of Protein Research, Russian Academy of Sciences, 4 Institutskaya Str., Pushchino 142292, Moscow region, Russia. alexey_surin@mail.ru.
authors: Alexey K
authors: AK
authors: Surin
authors: Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland.Departments of Chemistry and Molecular Biosciences, Northwestern University, 2170 Campus Drive, Evanston, Illinois 60208. luca.fornelli@northwestern.edu.
authors: Luca
authors: L
authors: Fornelli
authors: V.L. Talrose Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences, 38 Leninsky Pr., Bld. 2, Moscow 119334, Russia. pridatchenkoml@gmail.com.
authors: Marina L
authors: ML
authors: Pridatchenko
authors: Institute of Protein Research, Russian Academy of Sciences, 4 Institutskaya Str., Pushchino 142292, Moscow region, Russia. marrruko@yandex.ru.
authors: Mariya Yu
authors: MY
authors: Suvorina
authors: V.L. Talrose Institute for Energy Problems of Chemical Physics, Russian Academy of Sciences, 38 Leninsky Pr., Bld. 2, Moscow 119334, Russia. Moscow Institute of Physics and Technology (State University), 9 Institutskii Per., Dolgoprudny 141700, Moscow region, Russia. mike.gorshkov@gmail.com.
authors: Mikhail V
authors: MV
authors: Gorshkov