The cation diffusion facilitator protein EmfA of Rhizobium etli belongs to a novel subfamily of Mn(2+)/Fe(2+) transporters conserved in α-proteobacteria

Metallomics. 2014 Oct;6(10):1808-15. doi: 10.1039/c4mt00135d. Epub 2014 Jul 23.


Manganese (Mn(2+)) plays a key role in important cellular functions such as oxidative stress response and bacterial virulence. The mechanisms of Mn(2+) homeostasis are not fully understood, there are few data regarding the functional and taxonomic diversity of Mn(2+) exporters. Our recent phylogeny of the cation diffusion facilitator (CDF) family of transporters classified the bacterial Mn(2+)-CDF transporters characterized to date, Streptococcus pneumoniae MntE and Deinococcus radiodurans DR1236, into two monophyletic groups. DR1236 was shown to belong to the highly-diverse metal specificity clade VI, together with TtCzrB, a Zn(2+)/Cd(2+) transporter from Thermus thermophilus, the Fe(2+) transporter Sll1263 from Synechocystis sp and eight uncharacterized homologs whose potential Mn(2+)/Zn(2+)/Cd(2+)/Fe(2+) specificities could not be accurately inferred because only eleven proteins were grouped in this clade. A new phylogeny inferred from the alignment of 197 clade VI homologs revealed three novel subfamilies of uncharacterized proteins. Remarkably, one of them contained 91 uncharacterized α-proteobacteria transporters (46% of the protein data set) grouped into a single subfamily. The Mn(2+)/Fe(2+) specificity of this subfamily was proposed through the functional characterization of the Rhizobium etli RHE_CH03072 gene. This gene was upregulated by Mn(2+), Zn(2+), Cd(2+) and Fe(2+) but conferred only Mn(2+) resistance to R. etli. The expression of the RHE_CH03072 gene in an E. coli mntP/zitB/zntA mutant did not relieve either Zn(2+) or Mn(2+) stress but slightly increased its Fe(2+) resistance. These results indicate that the RHE_CH03072 gene, now designated as emfA, encodes for a bacterial Mn(2+)/Fe(2+) resistance CDF protein, having orthologs in more than 60 α-proteobacterial species.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alphaproteobacteria / chemistry
  • Alphaproteobacteria / genetics
  • Alphaproteobacteria / metabolism
  • Amino Acid Sequence
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cation Transport Proteins / chemistry
  • Cation Transport Proteins / genetics
  • Cation Transport Proteins / metabolism*
  • Cations, Divalent / metabolism
  • Escherichia coli / genetics
  • Escherichia coli / metabolism
  • Gene Expression Regulation, Bacterial
  • Iron / metabolism*
  • Manganese / metabolism*
  • Molecular Sequence Data
  • Phylogeny
  • Rhizobium etli / chemistry
  • Rhizobium etli / genetics
  • Rhizobium etli / metabolism*
  • Sequence Alignment


  • Bacterial Proteins
  • Cation Transport Proteins
  • Cations, Divalent
  • Manganese
  • Iron