A viral protein that blocks Arf1-mediated COP-I assembly by inhibiting the guanine nucleotide exchange factor GBF1

Many viruses modify cellular processes for their own benefit. The enterovirus 3A protein inhibits endoplasmic reticulum (ER)-to-Golgi transport, a function previously suggested to be important for viral suppression of immune responses. Here, we show that a virus carrying a 3A protein defective in inhibiting ER-to-Golgi transport is indeed less virulent in mice, and we unravel the mechanism by which 3A inhibits this trafficking step. Evidence is provided that 3A inhibits the activation of the GTPase ADP-ribosylation factor 1 (Arf1), which regulates the recruitment of the COP4 coat complex to membranes. 3A specifically inhibits the function of GBF1, a guanine nucleotide exchange factor for Arf1, by interacting with its N terminus. By specifically interfering with GBF1-mediated Arf1 activation, 3A may prove a valuable tool in dissecting the early steps of the secretory pathway.