Quantifying labile protein—Ligand interactions using electrospray ionization mass spectrometry

  • Amr El-Hawiet
  • Elena N. Kitova
  • Lan Liu
  • John S. Klassen
Article

Abstract

A new electrospray ionization mass spectrometry (ES-MS) approach for quantifying protein—ligand complexes that are prone to in-source (gas-phase) dissociation is described. The method, referred to here as the reference ligand ES-MS method, is based on the direct ES-MS assay and competitive ligand binding. A reference ligand (Lref), which binds specifically to the protein (P), at the same binding site as the ligand (L) of interest, with known affinity and forms a stable protein—ligand complex in the gas phase, is added to the solution. The fraction of P bound to Lref, which is determined directly from the ES mass spectrum, is sensitive to the fraction of P bound to L in solution and enables the affinity of P for L to be determined. A mathematical framework for the implementation of the method in cases where P has one or two specific ligand binding sites is given. Affinities of two carbohydrate-binding proteins, a single chain fragment of a monoclonal antibody and the lectin concanavalin A, for monosaccharide ligands are reported and the results are shown to agree with values obtained using isothermal titration calorimetry.

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Copyright information

© American Society for Mass Spectrometry 2010

Authors and Affiliations

  • Amr El-Hawiet
    • 1
  • Elena N. Kitova
    • 1
  • Lan Liu
    • 1
  • John S. Klassen
    • 1
  1. 1.Alberta Ingenuity Centre for Carbohydrate Science, Department of ChemistryUniversity of AlbertaEdmontonCanada

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