Primary Citation of Related Structures: 2VNS, 2VQ3
PubMed Abstract:
The daily production of 200 billion erythrocytes requires 20 mg of iron, accounting for nearly 80% of the iron demand in humans. Thus, erythroid precursor cells possess an efficient mechanism for iron uptake in which iron loaded transferrin (Tf) binds to the transferrin receptor (TfR) at the cell surface ...
The daily production of 200 billion erythrocytes requires 20 mg of iron, accounting for nearly 80% of the iron demand in humans. Thus, erythroid precursor cells possess an efficient mechanism for iron uptake in which iron loaded transferrin (Tf) binds to the transferrin receptor (TfR) at the cell surface. The Tf:TfR complex then enters the endosome via receptor-mediated endocytosis. Upon endosomal acidification, iron is released from Tf, reduced to Fe(2+) by Steap3, and transported across the endosomal membrane by divalent metal iron transporter 1. Steap3, the major ferrireductase in erythrocyte endosomes, is a member of a unique family of reductases. Steap3 is comprised of an N-terminal cytosolic oxidoreductase domain and a C-terminal heme-containing transmembrane domain. Cytosolic NADPH and a flavin are predicted cofactors, but the NADPH/flavin binding domain differs significantly from those in other eukaryotic reductases. Instead, Steap3 shows remarkable, although limited homology to FNO, an archaeal oxidoreductase. We have determined the crystal structure of the human Steap3 oxidoreductase domain in the absence and presence of NADPH. The structure reveals an FNO-like domain with an unexpected dimer interface and substrate binding sites that are well positioned to direct electron transfer from the cytosol to a heme moiety predicted to be fixed within the transmembrane domain. Here, we discuss possible gating mechanisms for electron transfer across the endosomal membrane.
Related Citations:
Identification of a Ferrireductase Required for Efficient Transferrin-Dependent Iron Uptake in Erythroid Cells Ohgami, R.S., Campagna, D.R., Greer, E.L., Antiochos, B., Mcdonald, A., Chen, J., Sharp, J.J., Fujiwara, Y., Barker, J.E., Fleming, M.D. (2005) Nat Genet 37: 1264
Nm1054, a Spontaneous, Recessive, Hypochromic, Microcytic Anemia Mutation in the Mouse Ohgami, R.S., Campagna, D.R., Antiochos, B., Wood, E.B., Sharp, J.J., Barker, J.E., Fleming, M.D. (2005) Blood 106: 3625
Organizational Affiliation:
Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717, USA.
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