Identification of the Escherichia coli K-12 Nramp orthologue (MntH) as a selective divalent metal ion transporter

The Escherichia coli mntH (formerly yfeP) gene encodes a putative membrane protein (MntH) highly similar to members of the eukaryotic Nramp family of divalent metal ion transporters. To determine the function of E. coli MntH, a null mutant was created and MntH was overexpressed both in wild-type E. coli and in the metal-dependent mutant hflB1(Ts). At the restrictive temper ature 42 degrees C, the mntH null mutation reduces the suppression of hflB1 (Ts) thermosensitivity by exogenous divalent metals. Conversely, overexpres sion of MntH restores growth at 42 degrees C, increases suppression of the ts phenotype by Fe(II) and Ni(II) and renders hflB1(Ts) cells hypersensitiv e to Mn(II). Transport studies in intact cells show that MntH selectively f acilitates uptake of Mn-54(II) and Fe-55(II) in a temperature-, time- and p roton-dependent manner. Competition studies in uptake assays and growth inh ibition experiments in hflB1(Ts) mutants together indicate that MntH is a d ivalent metal cation transporter of broad substrate specificity. The functi onal characteristics of MntH suggest that it corresponds to the previously described manganese transporter of E. coli. This study indicates that proto n-dependent divalent metal ion uptake has been preserved in the Nramp famil y from bacteria to humans.