Iron transport by Nramp2/DMT1: pH regulation of transport by 2 histidines in transmembrane domain 6.
Mutations at natural resistance-associated macrophage protein 1 (Nramp1) impair phagocyte function and cause susceptibility to infections while mutations at Nramp2 (divalent metal transporter 1 [DMT1]) affect iron homeostasis and cause severe microcytic anemia. Structure-function relationships in the Nramp superfamily were studied by mutagenesis, followed by functional characterization in yeast and in mammalian cells. These studies identify 3 negatively charged and highly conserved residues in transmembrane domains (TM) 1, 4, and 7 as essential for cation transport by Nramp2/DMT1. The introduction of a charged residue (Gly185Arg) in TM4 found in the naturally occurring microcytic anemia mk (mouse) and Belgrade (rat) mutants is shown to cause a partial or complete loss of function in mammalian and yeast cells, respectively. A pair of mutation-sensitive and highly conserved histidines (His267, His272) was identified in TM6. Surprisingly, inactive His267 and His272 mutants could be rescued by lowering the pH of the transport assay. This indicates that His267/His272 are not directly involved in metal binding but, rather, play an important role in pH regulation of metal transport by Nramp proteins.
Lam-Yuk-Tseung
Steven
S
Department of Biochemistry, McGill Cancer Center and Center for Host Resistance, McGill University, Montreal, QC, Canada.
Govoni
Gregory
G
Forbes
John
J
Gros
Philippe
P
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000740:Anemia / Q000235:genetics / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics; D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D002413:Cations, Divalent / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D005816:Genetic Complementation Test; D006639:Histidine / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport; D007501:Iron / Q000378:metabolism*; D033862:Iron-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics; D051379:Mice; D008817:Mice, Mutant Strains; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D020125:Mutation, Missense; D017354:Point Mutation; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D017434:Protein Structure, Tertiary; D051381:Rats; D011922:Rats, Mutant Strains; D011993:Recombinant Fusion Proteins / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology; D013329:Structure-Activity Relationship; D000099236:Solute Carrier Family 11, Member 2
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D002413:Cations, Divalent; D006639:Histidine; D007501:Iron; D033862:Iron-Binding Proteins; D008565:Membrane Proteins; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D000099236:Solute Carrier Family 11, Member 2; C105116:SMF1 protein, S cerevisiae; C416343:Smf2 protein, S cerevisiae