Pieces of the True Grail: A G Protein Finds Its Target

One of the first to be discovered and still one of the most important, cyclic AMP is a second messenger inside cells, carrying information from outside signals to change processes inside. As described by Bourne in his Perspective and reported by Tesmer et al. and Sunahara et al., adenylyl cyclase, the enzyme that catalyzes this process, has now been crystallized with the molecule that turns it on, the G protein G, yielding a first glimpse into the molecular details that underly this critical biochemical reaction.