Answer
Robert Lefkowitz and Brian Kobilka are two scientists who have worked together on the study of G protein-coupled receptors (GPCRs). GPCRs are a type of receptor that is found on the surface of cells and is activated by the binding of a ligand, such as a hormone or neurotransmitter. When a ligand binds to a GPCR, it causes the receptor to change shape, which in turn activates a G protein.