Membrane topology of the DrrB protein of the doxorubicin transporter of Streptomyces peucetius

Daunorubicin and doxorubicin, two commonly used anticancer agents, are produced by the soil bacterium Streptomyces peucetius. Self-resistance to these antibiotics in S. peucetius is conferred by the drrAB locus that codes for two proteins, DrrA and DrrB. DrrA is an ATP-binding protein. It belongs to the ABC family of transporters and shares sequence and functional similarities with P-glycoprotein of cancer cells. DrrB is an integral membrane protein that might function as a transporter for the efflux of daunorubicin and doxorubicin. Together, DrrA and DrrB are believed to form an ATP-driven pump for the efflux of these drugs. The drrAB locus has been cloned, and the two proteins have been expressed in a functional form in Escherichia coli. A topological analysis of the DrrB protein was performed using gene fusion methodology. Random and site-directed fusions of the drrB gene to lacZ, phoA, or gfp reporter genes were created. Based on the fusion data, a topological model of the DrrB protein is proposed in which the protein has eight membrane-spanning domains with both the N terminus and the C terminus in the cytoplasm.