title: Evolution of differences in transport function in Slc11a family members.
abstract: Slc11a1 (formerly Nramp1) is a proton/divalent cation transporter that regulates cation homeostasis in macrophages. Slc11a2 mediates divalent cation uptake via the gut and delivery into cells. The mode of action of the two transporters remains controversial. Heterologous expression in frog oocytes shows Slc11a2 is a symporter, whereas Slc11a1 is an antiporter fluxing divalent cations against the proton gradient. This explains why Slc11a2, but not Slc11a1, can complement EGTA sensitivity in smf1Delta/smf2Delta/smf3Delta yeast. However, some studies of transport in mammalian cells suggest Slc11a1 is a symporter. We now demonstrate that Slc11a1, but not Slc11a2, complements a divalent cation stress phenotype in bsd2Delta/rer1Delta yeast. This is the first description of a yeast complementation assay for Slc11a1 function. Given the prior demonstration in frog oocytes that Slc11a1 acts as an antiporter, the most plausible interpretation of the data is that Slc11a1 is rescuing bsd2Delta/rer1Delta yeast by exporting divalent cations. Chimaeras define the N terminus, and a segment of the protein core preceding transmembrane domain 9 through transmembrane domain 12, as important in rescuing the divalent cation stress phenotype. EGTA sensitivity and divalent cation stress phenotypes in yeast expressing Slc11a orthologues show that symport activity is ancestral. Molecular changes that mediate rescue of the divalent cation stress phenotype post-date frogs and co-evolved with Slc11a1 orthologues that regulate divalent cation homeostasis in macrophages and resistance to infection in chickens and mammals.
authors.affiliation: Cambridge Institute for Medical Research, Wellcome Trust/MRC Building, University of Cambridge School of Clinical Medicine, Addenbrookes Hospital, Hills Road, Cambridge CB2 2XY, UK.
authors.forename: Michala Eichner
authors.initials: ME
authors.lastname: Techau
authors.forename: Javier
authors.initials: J
authors.lastname: Valdez-Taubas
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Popoff
authors.forename: Richard
authors.initials: R
authors.lastname: Francis
authors.forename: Matthew
authors.initials: M
authors.lastname: Seaman
authors.forename: Jenefer M
authors.initials: JM
authors.lastname: Blackwell
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002413:Cations, Divalent / Q000378:metabolism; D002645:Chickens; D019143:Evolution, Molecular; D005260:Female; D015870:Gene Expression; D005816:Genetic Complementation Test; D006801:Humans; D017136:Ion Transport / Q000235:genetics; D008264:Macrophages / Q000378:metabolism; D050506:Mutant Chimeric Proteins / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis; D000099173:Natural Resistance-associated Macrophage Protein 1; D000099236:Solute Carrier Family 11, Member 2
chemical_list: D027682:Cation Transport Proteins; D002413:Cations, Divalent; D050506:Mutant Chimeric Proteins; D000099173:Natural Resistance-associated Macrophage Protein 1; D000099236:Solute Carrier Family 11, Member 2