Move It on Out with MATEs

Multidrug transporters form a large class of membrane proteins present in the cells of most organisms. These proteins bind to a variety of potentially cytotoxic compounds and remove them from the cell in an ATPor protondependent process (Zhelenova et al., 2000). Traditionally, multidrug transporters have been divided into four superfamilies: the ATP binding cassette (ABC) superfamily, the major facilitator superfamily, the small multidrug resistance family, and the resistance-nodulation-cell division family. Brown et al. (1999) defined a fifth family, called the multidrug and toxic compound extrusion (MATE) family of transporters. The MATE family is characterized by the presence of 12 putative transmembrane segments and by the absence of “signature sequences” specific to the other multidrug transporter superfamilies. MATE proteins are believed to function as proton-dependent efflux transporters, based on the genetic characterization of two family members, NorM from Vibrio parahaemolyticus and its homolog YdeH from Escherichia coli . Expression of these proteins in E. coli confers resistance to various antibiotics and antimicrobial agents that is dependent on the maintenance of a proton gradient across the plasma membrane. MATE genes are abundant in bacteria and plants—the Arabidopsis genome contains at least 54 MATE family members—but have not been found in mammals. Aside from NorM and YdeH, very little functional information is available on these proteins. In this issue of The Plant Cell , Diener et al. (pages 1625–1637) describe the functional analysis of the MATE gene ALF5 in Arabidopsis. The alf5 mutant exhibits greatly inhibited formation of lateral roots when grown in commercial Bacto agar (Figure 1). Interestingly, it was found Move It on Out with MATEs