title: Comparison between enhanced MALDI in-source decay by ammonium persulfate and N- or C-terminal derivatization methods for detailed peptide structure determination.
abstract: Amino acid sequencing and more detailed structure elucidation analysis of peptides and small proteins is a very difficult task even if state-of-the-art mass spectrometry (MS) is employed. To make this task easier, chemical derivatization methods of the N terminus with 4-sulfophenyl-isothiocyanate (SPITC) or the C terminus with 2-methoxy-4,5-dihydro-1H-imidazole (Lys-tag) can enhance peptide fragmentation or fragment ionizability, via proton mobility/localization mechanisms making tandem MS (MS(2)) spectra more informative and less demanding for structural interpretation. Observed disadvantages related to both derivatization methods are sample- and time-consuming procedures and the increased number of reaction byproducts. A novel, sulfate radical in-source formation method of matrix-assisted laser desorption ionization (MALDI) MS based on chemically enhanced in-source decay (ISD) can be accomplished by simple addition of ammonium persulfate (APS) in the matrix solution. This method enables effective decomposition of peptide ions already in the first stage of MS analysis where a large number of fragment ions are produced. The resultant MALDI-ISD mass spectra (MS after APS → MALDI-ISD MS) are almost equivalent to conventional, collision-induced dissociation (CID) MS(2) spectra. These fragment ions are further subjected to the second stage of the MS, and consequently, MS(3) spectra are produced, which makes the sequence analysis more informative and complete (CID MS(2) is thus equivalent to CID MS(3)). Multiply stage MS after APS addition showed enhanced sensitivity, resolution, and mass accuracy compared to peptide derivatization (SPITC and Lys-tag) or conventional MS and MS(2) analyses and offered more detailed insight into peptide structure.
authors.affiliation: Ruđer Bošković Institute, Bijenička cesta 54, Zagreb, Croatia.
authors.forename: Anita
authors.initials: A
authors.lastname: Horvatić
authors.forename: Ivana
authors.initials: I
authors.lastname: Dodig
authors.forename: Tomislav
authors.initials: T
authors.lastname: Vuletić
authors.forename: Dubravko
authors.initials: D
authors.lastname: Pavoković
authors.forename: Zdenko
authors.initials: Z
authors.lastname: Hameršak
authors.forename: Ana
authors.initials: A
authors.lastname: Butorac
authors.forename: Mario
authors.initials: M
authors.lastname: Cindrić
mesh_terms: D000595:Amino Acid Sequence; D000645:Ammonium Sulfate / Q000737:chemistry*; D001557:Benzenesulfonates / Q000737:chemistry*; D017576:Daptomycin / Q000737:chemistry*; D000077560:Enfuvirtide; D015700:HIV Envelope Protein gp41 / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D017879:Isothiocyanates / Q000737:chemistry*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis* / Q000737:chemistry; D012680:Sensitivity and Specificity; D020539:Sequence Analysis, Protein; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods / Q000592:standards*; D014357:Trypsin
chemical_list: C447410:2-methoxy-4,5-dihydro-1H-imidazole; D001557:Benzenesulfonates; D015700:HIV Envelope Protein gp41; D007093:Imidazoles; D017879:Isothiocyanates; D010446:Peptide Fragments; D000077560:Enfuvirtide; C031276:ammonium peroxydisulfate; C015308:4-isothiocyanatobenzenesulfonate; D014357:Trypsin; D017576:Daptomycin; D000645:Ammonium Sulfate