Genetic analysis of Saccharomyces cerevisiae Pdr5p/substrate interactions

The ATP-binding cassette superfamily of transporters occurs in all organisms that have been studied. Its members include a subset of large, membrane proteins that detoxify cells from xenobiotic compounds. Although such transporters are of tremendous clinical relevance, many features of their structure and function are poorly understood. For instance, it is not always clear whether a particular eukaryotic transporter functions in vivo as a monomer or a multimer. In this study, several site-directed mutations were constructed in the transmembrane domains of the yeast multidrug efflux pump Pdr5p. One of these, S558Y, binds ATP, but fails to hydrolyze the nucleotide or transport rhodamine 6G, a Pdr5p transport substrate. Additional analysis of this mutant strongly indicated that Pdr5p functions as a monomer. Furthermore, S558 might identify a region that is critical for proper cross-talk between the ATP-binding and substrate transport domains.