Sensing Protein Surfaces with Targeted Fluorescent Receptors

A methodology for creating fluorescent molecular sensors that respond to changes that occur on the surfaces of specific proteins is presented. This approach, which relies on binding cooperatively between a specific His‐tag binder and a nonspecific protein‐surface receptor, enabled the development of a sensor that can track changes on the surface of a His‐tag‐labeled calmodulin (His‐CaM) upon interacting with metal ions, small molecules, and protein binding partners. The way this approach was used to detect dephosphorylation of an unlabeled calmodulin‐dependent protein kinase II (CaMKII), and the binding of Bax BH3 to His‐tagged B‐cell lymphoma 2 (Bcl‐2) protein is also presented. Tracking changes in the surfaces of His‐tag‐labeled proteins with fluorescent molecular sensors becomes possible by integrating a specific His‐tag binder (I), a nonspecific protein‐surface receptor (II), and a solvatochromic probe (III) on a single molecular platform. This approach enabled the detection of protein‐surface modifications resulting from various binding interactions (see scheme).