Gs alpha meets its target--shedding light on a key signal transduction event.

The recently determined crystal structure of Gs alpha bound to a catalytically active form of adenylyl cyclase reveals the location of the enzyme's active site and provides the first view of heterotrimeric G protein alpha subunit activating a downstream effector. Comparison with the structure of a catalytically inactive form of adenylyl cyclase suggests a plausible allosteric mechanism whereby the synergistic activators Gs alpha and forskolin stimulate the activity of adenylyl cyclase.