title: Selective and nonselective cleavages in positive and negative CID of the fragments generated from in-source decay of intact proteins in MALDI-MS.
abstract: Selective and nonselective cleavages in ion trap low-energy collision-induced dissociation (CID) experiments of the fragments generated from in-source decay (ISD) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) of intact proteins are described in both positive and negative ion modes. The MALDI-ISD spectra of the proteins demonstrate common, discontinuous, abundant c- and z'-ions originating from cleavage at the N-Cα bond of Xxx-Asp/Asn and Gly-Xxx residues in both positive- and negative-ion modes. The positive ion CID of the c- and z'-ions resulted in product ions originating from selective cleavage at Asp-Xxx, Glu-Xxx and Cys-Xxx residues. Nonselective cleavage product ions rationalized by the mechanism of a "mobile proton" are also observed in positive ion CID spectra. Negative ion CID of the ISD fragments results in complex product ions accompanied by the loss of neutrals from b-, c-, and y-ions. The most characteristic feature of negative ion CID is selective cleavage of the peptide bonds of acidic residues, Xxx-Asp/Glu/Cys. A definite influence of α-helix on the CID product ions was not obtained. However, the results from positive ion and negative ion CID of the MALDI-ISD fragments that may have long α-helical domains suggest that acidic residues in helix-free regions tend to degrade more than those in helical regions.
authors.affiliation: Graduate School in Nanobioscience, Mass Spectrometry Laboratory, Yokohama City University, Kanazawa-ku, Yokohama, Japan, takayama@yokohama-cu.ac.jp.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Takayama
authors.forename: Sadanori
authors.initials: S
authors.lastname: Sekiya
authors.forename: Ryunosuke
authors.initials: R
authors.lastname: Iimuro
authors.forename: Shinichi
authors.initials: S
authors.lastname: Iwamoto
authors.forename: Koichi
authors.initials: K
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D006736:Horses; D006859:Hydrogen; D007477:Ions / Q000737:chemistry / Q000378:metabolism; D010100:Oxygen; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D007477:Ions; D011506:Proteins; D006859:Hydrogen; D010100:Oxygen