THE MTRD PROTEIN OF NEISSERIA-GONORRHOEAE IS A MEMBER OF THE RESISTANCE NODULATION/DIVISION PROTEIN FAMILY CONSTITUTING PART OF AN EFFLUX SYSTEM/

The mtr (multiple transferable resistance) system of Neisseria gonorrh oeae mediates resistance of gonococci to structurally diverse hydropho bic agents (HAs) through an energy-dependent efflux process, Recently, complete or partial ORFs that encode membrane proteins (MtrC, MtrD, M trE) forming an efflux pump responsible for removal of HAs from gonoco cci were identified and appeared to constitute a single transcriptiona l unit. In this study, the complete nucleotide sequence of the mtrD ge ne was determined, permitting the characterization of the MtrD protein . The full-length MtrD protein has a predicted molecular mass of nearl y 114 kDa, putatively containing a 56 amino acid signal peptide. MtrD displays significant amino acid sequence similarity to a family of cyt oplasmic membrane proteins, termed resistance/nodulation/division (RND ) proteins, which function as energy-dependent transporters of antibac terial agents and secrete bacterial products to the extracellular flui d, The predicted topology of the MtrD transporter protein revealed 12 potential membrane-spanning domains, which were clustered within the c entral and C-terminal regions of the primary sequence, Loss of MtrD du e to insertional inactivation of the mtrD gene rendered gonococci hype rsusceptible to several structurally diverse HAs, including two fatty acids (capric acid and palmitic acid) and a bile salt (cholic acid), b ut not hydrophilic antibiotics such as ciprofloxacin and streptomycin. Since gonococci often infect mucosal sites rich in toxic fatty acids and bile salts, the expression of the mtr efflux system may promote gr owth of gonococci under hostile conditions encountered in vivo.