The consequences of agonist-dependent activation of guanine nucleotide-binding protein (G protein)coupled receptors vary from cell to cell, depending on a complex network of regulations between components of the signaling cascade. Specific interactions between receptors, G proteins, and effecters are difficult to analyze in intact cells. Engineering of receptor-transducer fusion proteins might be an effective strategy to target cellular effecters more efficiently and specifically. As a model, we evaluated the ability of a fusion protein of beta(2)-adrenergic receptor bound to the cu subunit of adenylyl cyclase-stimulatory G protein (G(s) alpha) to restore the defective activation of adenylyl cyclase in S49 cyc- cells that lack endogenous G(s) alpha. The coupling between the two partners of the fusion protein was functional, and the agonist-dependent activation of the effector was more potent and more productive in transfected than in wild-type S49 cells. The covalent link between receptor and G(s) alpha could thus convey an advantage over freely interacting components. Such receptor-G alpha fusion proteins may help to elucidate the complex interactions between members of signaling pathways and may also constitute a useful tool for studying the effects of single effector activation.
