Effect of amino acid side-chain on fragmentation of cyclic peptide ions: differences of ESI-MS/CID mass spectra of toxic heptapeptide microcystins containing ADMAdda instead of Adda

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Eur. J. Mass Spectrom. 4, 287 - 298 (1998)

Effect of amino acid side-chain on fragmentation of cyclic peptide ions: differences of ESI-MS/CID mass spectra of toxic heptapeptide microcystins containing ADMAdda instead of Adda

Moucun Yuan, Michio Namikoshi and Akira Otsuki^*
Department of Ocean Sciences, Tokyo University of Fisheries, Minato-ku, Tokyo 108, Japan. E-mail: .
Kaarina Sivonen
Department of Applied Chemistry and Microbiology, PO Box 56, 00014 University of Helsinki, Finland.

ABSTRACT:

Characteristics of collision-induced decomposition (CID) spectra recorded following electrospray ionization (ESI) of toxic heptapeptide microcystins containing (2S,3S,8S,9S)-3-amino-9-acetoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (ADMAdda) have been investigated in detail and compared with those from compounds containing (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (Adda). A significant difference in their CID spectra was observed in the cleavage of cyclic structures in low-energy CID processes due to the effect of the amino acid side-chain on fragmentation. Microcystins containing ADMAdda produced mostly b-type ions. Fragment ions predicted on the basis of the known fragmentation of cyclic peptides and linear-peptide b-type ions, predicted by the Peptide Matching (PEPM) program, matched well with peaks in the CID spectra. A neutral loss of CH₃COOH from the ADMAdda residues was observed in the CID spectra of doubly charged ions, [M + 2H]²⁺. The present study suggested that the CID spectra of [M + H]⁺ and [M + 2H]²⁺ ions can provide their sequence information.

Keywords: Two-component signal transduction proteins, on-target proteolysis, structure/function correlation, MALDI-MS, ESI-MS

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