InCELL Pulse cellular target engagement assays measure compound binding to a cellular target by detecting changes in protein thermal stability. In this assay, the target is fused to the enhanced ProLabel® (ePL) enzyme fragment and expressed in the selected cell background. The fusion is detected with high sensitivity through the addition of a substrate and complementary enzyme acceptor fragment (EA) in the presence of a cell lysis buffer. The ePL tag is an ideal fusion partner for InCELL Pulse for the following reasons: 1) ePL is a small unstructured peptide (42 aa) that does not affect the tagged protein’s thermal denaturation profile; 2) ePL enables simple, sensitive, and precise fusion protein detection; and 3) the sensitivity of ePL detection depends on the macromolecular state of the fusion protein. Whereas native properly folded ePL fusion proteins are detected with high sensitivity, denatured aggregated states of fusion proteins are poorly detected. The ability of ePL to report on a fusion protein’s macromolecular state is the basis of the InCELL Pulse technology because ligand binding can protect proteins from thermal denaturation. For a detailed description of the InCELL Pulse assay principle, please refer to the user manual. The provided cells are for single use only and have been prepared such that target expression reduces dramatically upon passaging.