Brefeldin A is a lactone antibiotic produced by fungal organisms such as Eupenicillium brefeldianum. Brefeldin A inhibits protein transport from the endoplasmic reticulum (ER) to the Golgi apparatus indirectly by preventing formation of COPII-mediated transport vesicles. Brefeldin A was initially isolated as an anti-viral antibiotic but is now primarily used in biological research to study protein transport. Brefeldin A forms a clear colorless solution at 10 mg/ml in both dichloromethane and methanol. In mammalian and yeast cells, the main target of brefeldin A appears to be a Guanine nucleotide exchange factor called Sar1. Sar1 mediates formation of transport vesicles by recruiting COPII coat proteins to cargo-bound receptor proteins found in the membrane of the rough ER. Inhibition of Sar1 activity prevents the anterograde movement of secretory proteins out of the ER.
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