Brefeldin A is a lactone antibiotic produced by fungal organisms such as Eupenicillium brefeldianum. Brefeldin A inhibits transport of proteins from ER to Golgi and induces retrograde protein transport from the Golgi apparatus to the endoplasmic reticulum. This leads to proteins accumulating inside the ER. In mammalian and yeast cells, the main target of brefeldin A appears to be a certain type of GTP-exchange factors responsible for activating a GTPase called Arf1p ; in turn, Arf1p is involved in the formation of transport vesicles by recruiting coat proteins to intracellular membranes. Brefeldin A was initially isolated as an anti-viral antibiotic but is now primarily used in biological research to study protein transport.



Brefeldin A affects COPI coat formation, which is involved in retrograde transport. It inhibits ArfI activation, prohibiting recruitment of COPI coat proteins to the budding vesicle by binding to its guanine exchange factor.