Measuring Sphingosine-1-Phosphate/Protein Interactions with the Kinetic Exclusion Assay

Methods Mol Biol. 2018:1697:1-8. doi: 10.1007/7651_2017_5.


By directly detecting the ligand-free binding sites in a sample, the kinetic exclusion assay (KinExA®) provides a compelling alternative to SPR-based techniques for determining equilibrium dissociation constants of protein-ligand interactions. It is especially useful for observing protein-lipid interactions, as binding of native lipids occurs entirely in solution, and monoclonal antibodies can be used to directly compete with a protein of interest for lipid binding. By measuring the antigen-free binding sites on the antibody and using competition affinity analysis, the K d for the lipid binding the protein and the antibody can be determined simultaneously. Herein, we describe this label-free approach for determining the K d for S1P-binding serum albumin, which chaperones ~30% of the S1P in human plasma.

Keywords: Anti-lipid antibody; Bovine serum albumin; Competitive affinity analysis; Human serum albumin; Kinetic exclusion assay; Physical biochemistry; Sphingosine-1-phosphate.

MeSH terms

  • Binding Sites
  • Humans
  • Kinetics
  • Lysophospholipids / metabolism*
  • Protein Binding
  • Serum Albumin, Human / chemistry
  • Serum Albumin, Human / metabolism*
  • Sphingosine / analogs & derivatives*
  • Sphingosine / metabolism


  • Lysophospholipids
  • sphingosine 1-phosphate
  • Sphingosine
  • Serum Albumin, Human