Journal
ANALYTICAL CHEMISTRY
Volume 84, Issue 11, Pages 4957-4964Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ac300607y
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- ANR [BLAN_NT09_692063]
- TGE-FTICR (CNRS)
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Characterizing the conformation of biomolecules by mass spectrometry still represents a challenge. With their knotted structure involving a N-terminal macrolactam ring where the C-terminal tail of the peptide is threaded and sterically trapped, lasso peptides constitute an attractive model for developing methods for characterizing gas-phase conformation, through comparison with their unknotted topoisomers. Here, the kinetics of electron capture dissociation (ECD) of a lasso peptide, capistruin, was investigated by electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry and compared to that of its branched-cyclic topoisomer, lactam-capistruin. Both peptides produced rather similar ECD spectra but showed different extent of H-center dot transfer from c(i)(I) to z(j)(center dot) ions. Time-resolved double-resonance experiments under ECD conditions were performed to measure the formation rate constants of typical product ions. Such experiments showed that certain product ions, in particular those related to H-center dot transfer, proceeded through long-lived complexes for capistruin, while fast dissociation processes predominated for lactam-capistruin. The formation rate constants of specific ECD product ions enabled a clear differentiation of the lasso and branched-cyclic topoisomers. These results indicate that the formation kinetics of ECD product ions constitute a new way to explore the conformation of biomolecules and distinguish between topoisomers and, more generally, conformers.
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