MDR proteins, they use energy to pump drugs out of the cell before the drugs can actually carry out or elicit their effects. And this is what our MDR protein looks like. So notice, the MDR protein consists of four domains. So even though in this case it's a single polypeptide chain, it contains four different domains. Two of these domains are shown here, they're essentially the transmembrane domains and the other two domains are shown here. They're called the ATP binding domains or ATP binding cassettes.