title: Dissociation of deprotonated microcystin variants by collision-induced dissociation following electrospray ionization.
abstract: Microcystins (MC) are a family of hepatotoxic cyclic heptapeptides produced by a number of different cyanobacterial species. Considering the recent advances in the characterization of deprotonated peptides by mass spectrometry, the fragmentation behavior of four structurally related microcystin compounds was investigated using collision-induced dissociation (CID) experiments on an orbitrap mass spectrometer. It is demonstrated in this study that significant structural information can be obtained from the CID spectra of deprotonated microcystins. A predominant ring-opening reaction at the isoMeAsp residue, as well as two major complementary fragmentation pathways, was observed, reducing the complexity of the product ion spectra in comparison with spectra observed from protonated species. This proposed fragmentation behavior was applied to characterize [Leu(1)]MC-LR from a cyanobacterial cell extract. In conclusion, CID spectra of microcystins in the negative ion mode provide rich structurally informative mass spectra which greatly enhance confidence in structural assignments, in particular when combined with complementary positive ion CID spectra.
authors.affiliation: Departamento de Análises Clínicas e Toxicológicas, Faculdade de Ciências Farmacêuticas, Universidade de São Paulo, São Paulo, SP, Brazil.
authors.forename: Felipe Augusto
authors.initials: FA
authors.lastname: Dörr
authors.forename: Diogo
authors.initials: D
authors.lastname: Oliveira-Silva
authors.forename: Norberto Peporine
authors.initials: NP
authors.lastname: Lopes
authors.forename: Jacobo
authors.initials: J
authors.lastname: Iglesias
authors.forename: Dietrich A
authors.initials: DA
authors.lastname: Volmer
authors.forename: Ernani
authors.initials: E
authors.lastname: Pinto
mesh_terms: D007477:Ions / Q000737:chemistry; D052998:Microcystins / Q000737:chemistry*; D046931:Microcystis / Q000737:chemistry; D008958:Models, Molecular; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D007477:Ions; D052998:Microcystins; D011522:Protons