There is a growing need to study ligand binding to proteins in native or complex solution using isothermal titration calorimetry (ITC). For example, it is desirable to measure ligand binding to membrane proteins in more native lipid-like environments such as bicelles, where ligands can access both sides of the membrane in a homogeneous environment. A critical step to obtain high signal-to-noise is matching the reaction chamber solution to the ligand solution, typically through a final dialysis or gel filtration step. However, to obtain reproducible bicelles, the lipid concentrations must be carefully controlled which eliminates the use of dialysis that can disrupt these parameters. Here, we report and validate a rapid preparation ITC (RP-ITC) approach to measure ligand binding without the need for a dialysis step. This general approach is used to quantify ion binding to a K+ channel embedded in bicelles and can be applied to complex, less defined systems.
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