Multistep tandem mass spectrometry for sequencing cyclic peptides in an ion-trap mass spectrometer.
Collisionally activated decomposition (CAD) of a protonated cyclic peptide produces a superposition spectrum consisting of fragments produced following random ring opening of the cyclic peptide to give a set of acylium ions (or isomeric equivalents) of the same m/z. Assignment of the correct sequence is often difficult owing to lack of selectivity in the ring opening. A method is presented that utilizes multiple stages of CAD experiments in an electrospray ion-trap mass spectrometer to sequence cyclic peptides. A primary acylium ion is selected from the primary product-ion spectrum and subjected to several stages of CAD. Amino-acid residues are sequentially removed, one at each stage of the CAD, from the C-terminus, until a b2 ion is reached. Results are presented for seven cyclic peptides, ranging in sizes from four to eight amino-acid residues. This method of sequencing cyclic peptides eliminates ambiguities encountered with other MS/MS approaches. The power of the strategy lies in the capability to execute several stages of CAD upon a precursor ion and its decomposition products, allowing the cyclic peptide to be sequenced in an unambiguous, stepwise manner.
Ngoka
L C
LC
Department of Chemistry, Washington University, St. Louis, Missouri 63130, USA.
Gross
M L
ML
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D065128:Endothelin Receptor Antagonists; D013058:Mass Spectrometry; D010456:Peptides, Cyclic / Q000737:chemistry*; D044022:Receptor, Endothelin A; D016339:Spectrometry, Mass, Fast Atom Bombardment; D013501:Surface-Active Agents
D000596:Amino Acids; D065128:Endothelin Receptor Antagonists; D010456:Peptides, Cyclic; D044022:Receptor, Endothelin A; D013501:Surface-Active Agents