Proximity-enhanced SuFEx chemical cross-linker for specific and multitargeting cross-linking mass spectrometry

Proc Natl Acad Sci U S A. 2018 Oct 30;115(44):11162-11167. doi: 10.1073/pnas.1813574115. Epub 2018 Oct 15.


Chemical cross-linking mass spectrometry (CXMS) is being increasingly used to study protein assemblies and complex protein interaction networks. Existing CXMS chemical cross-linkers target only Lys, Cys, Glu, and Asp residues, limiting the information measurable. Here we report a "plant-and-cast" cross-linking strategy that employs a heterobifunctional cross-linker that contains a highly reactive succinimide ester as well as a less reactive sulfonyl fluoride. The succinimide ester reacts rapidly with surface Lys residues "planting" the reagent at fixed locations on protein. The pendant aryl sulfonyl fluoride is then "cast" across a limited range of the protein surface, where it can react with multiple weakly nucleophilic amino acid sidechains in a proximity-enhanced sulfur-fluoride exchange (SuFEx) reaction. Using proteins of known structures, we demonstrated that the heterobifunctional agent formed cross-links between Lys residues and His, Ser, Thr, Tyr, and Lys sidechains. This geometric specificity contrasts with current bis-succinimide esters, which often generate nonspecific cross-links between lysines brought into proximity by rare thermal fluctuations. Thus, the current method can provide diverse and robust distance restraints to guide integrative modeling. This work provides a chemical cross-linker targeting unactivated Ser, Thr, His, and Tyr residues using sulfonyl fluorides. In addition, this methodology yielded a variety of cross-links when applied to the complex Escherichia coli cell lysate. Finally, in combination with genetically encoded chemical cross-linking, cross-linking using this reagent markedly increased the identification of weak and transient enzyme-substrate interactions in live cells. Proximity-dependent cross-linking will dramatically expand the scope and power of CXMS for defining the identities and structures of protein complexes.

Keywords: chemical cross-linker; cross-linking mass spectrometry; protein–protein interaction; proximity-enhanced reactivity; sulfur–fluoride exchange.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acids / chemistry
  • Cross-Linking Reagents / chemistry*
  • Escherichia coli / metabolism
  • Fluorides / chemistry*
  • Lysine / chemistry
  • Mass Spectrometry / methods
  • Proteins / chemistry
  • Succinimides / chemistry
  • Sulfur Compounds / chemistry*


  • Amino Acids
  • Cross-Linking Reagents
  • Proteins
  • Succinimides
  • Sulfur Compounds
  • sulfur fluoride
  • succinimide
  • Lysine
  • Fluorides