Turning on ARF: the Sec7 family of guanine-nucleotide-exchange factors

ARF proteins are important regulators of membrane dynamics mid protein transport within the eukaryotic cell. The Sec7 domain is similar to 200 amino acids in size and stimulates guanine-nucleotide exchange on members of the ARF class of small GTPases. The members of one subclass of Sec7-domain proteins are direct targets of the secretion-inhibiting drug brefeldin A, which blocks the exchange reaction by trapping a reaction intermediate in an inactive, abortive complex. A separate subclass of Sec7-domain proteins is involved in signal transduction and possess a domain that mediates membrane binning in response to extracellular signals.