Top‐down ion mobility/mass spectrometry reveals enzyme specificity: Separation and sequencing of isomeric proteoforms

Francis Berthias, Nurgül Bilgin, Jasmin Mecinović, Ole N. Jensen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review


Enzymatic catalysis is one of the fundamental processes that drives the dynamic landscape of post-translational modifications (PTMs), expanding the structural and functional diversity of proteins. Here, we assessed enzyme specificity using a top-down ion mobility spectrometry (IMS) and tandem mass spectrometry (MS/MS) workflow. We successfully applied trapped IMS (TIMS) to investigate site-specific N-ε-acetylation of lysine residues of full-length histone H4 catalyzed by histone lysine acetyltransferase KAT8. We demonstrate that KAT8 exhibits a preference for N-ε-acetylation of residue K16, while also adding acetyl groups on residues K5 and K8 as the first degree of acetylation. Achieving TIMS resolving power values of up to 300, we fully separated mono-acetylated regioisomers (H4K5ac, H4K8ac, and H4K16ac). Each of these separated regioisomers produce unique MS/MS fragment ions, enabling estimation of their individual mobility distributions and the exact localization of the N-ε-acetylation sites. This study highlights the potential of top-down TIMS-MS/MS for conducting enzymatic assays at the intact protein level and, more generally, for separation and identification of intact isomeric proteoforms and precise PTM localization.

Original languageEnglish
Article number2200471
Issue number3-4
Number of pages11
Publication statusPublished - Feb 2024


  • chromatin
  • enzyme assay
  • epigenetics
  • ion mobility spectrometry
  • Tandem Mass Spectrometry
  • Protein Processing, Post-Translational
  • Acetylation
  • Ion Mobility Spectrometry/methods
  • Histones/metabolism


Dive into the research topics of 'Top‐down ion mobility/mass spectrometry reveals enzyme specificity: Separation and sequencing of isomeric proteoforms'. Together they form a unique fingerprint.

Cite this