Assessing Surface Binding Events on Golgi Microsomes Isolated from Cancer Cells by Capillary Electrophoresis.

Intracellular membrane proteins represent a vast and pharmacologically essential class of therapeutic targets, yet their characterization within native pathological environments remains experimentally challenging. Here, we report what is, to the best of our knowledge, the first direct affinity measurements performed at the surface of Golgi microsomes isolated from cancer cells. By integrating affinity capillary electrophoresis (ACE) with a refined mathematical framework, we overcome long-standing obstacles associated with membrane protein analysis, including the need for target modification, intrinsic enzymatic activity, labeled probe, or large protein excess. The microfluidic format further minimizes sample consumption while enabling both direct and indirect detection modalities, thereby expanding applicability to impure compounds and ligands lacking charge or UV absorbance. Applying this strategy to UGCG, a Golgi-resident membrane protein of oncological relevance, we demonstrate quantitative ligand-binding measurements on fairly monodisperse vesicular fractions (∼150 nm) that preserve native intracellular architecture. Collectively, this work establishes a robust, broadly applicable platform for target engagement studies in complex biological systems and highlights the potential of ACE to accelerate drug discovery efforts involving intracellular or extracellular membrane-bound targets.