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Updated: Jul 12, 2025

2D-HELS MS Seq: A General LC-MS-Based Method for Direct and de novo Sequencing of RNA Mixtures with Different Nucleotide Modifications
Published on: July 10, 2020
Sequencing of Morpholino Antisense Oligonucleotides Using Electron Capture Dissociation Mass Spectrometry
Kaoru Karasawa1, Eva Duchoslav2, Lyle Burton2
1SCIEX, 4-7-35 Kitashinagawa, Shinagawa, Tokyo 140-0001, Japan.
Abstract:
We report the first sequencing of morpholino antisense oligonucleotides (phosphorodiamidate morpholino oligomers, PMOs) using electron capture dissociation (ECD) mass spectrometry. In this research, we found dissociation of the backbone of 18- to 25-mer PMOs to produce d and z ions as the major ions, and 100% cleavage coverage (sequence coverage) was obtained with these ions. This is a critical contrast with beam-type collision-induced dissociation, which dominantly induces base loss, so it is difficult to obtain sequence information. The results showed that an electron beam energy (typically 15 eV) can be used universally for PMOs with different sequences, lengths, and charge states so that no detailed optimization is required for multiprecursor targeting liquid chromatography coupled with tandem mass spectrometry measurements. We also confirmed that the ECD reaction speed was compatible with the high-performance liquid chromatography time scale. Finally, we demonstrated a liquid chromatography electron capture dissociation tandem mass spectrometry workflow to survey the modification sites of the emulated PMO impurities.
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