Regulation of COPII‐mediated protein transport

The export of newly synthesized membrane proteins from the endoplasmic reticulum (ER) requires the action of coat protein complex II (COPII), which is comprised of five core subunits (Sar1, Sec23, Sec24, Sec13, and Sec31) that co-assemble to remodel membranes and generate transport carriers. Recent studies conducted in our lab demonstrate that COPII carrier biogenesis surprisingly continues in the absence of Sar1 GTPase activity, which was suggested previously to be indispensable for COPII-mediated membrane reorganization. Specifically, we show that inhibition of Sar1 stimulates ER stress and triggers the formation of unconventional transport carriers that are decorated with other COPII components and remain capable of directing secretory protein trafficking out of the ER. Our studies suggest new mechanisms by which COPII drives membrane remodeling independently of Sar1.