Snapshots form a big picture of guanine nucleotide exchange.

Small guanosine triphosphatases (GTPases) regulate a vast array of cellular functions. Their highly controlled activation, which is catalyzed by guanine nucleotide exchange factors (GEFs), links input signals emanating from various events such as stimulation of cell surface receptors to a similarly diverse range of downstream responses. Due to the central role of GEFs in the regulation of GTPase-mediated signaling processes, their mode of action has been intensively investigated. A new structural study on the DOCK family of Rho family-specific GEFs now uncovers an unusual variation in the way in which GEFs can regulate the nucleotide status of GTPases and provides the most complete picture of a GDP-GTP exchange cycle to date.