Ferroportin: lack of evidence for multimers.
Ferroportin is a multi-transmembrane glycoprotein that mediates iron export from cells. Mutations in ferroportin are linked to type IV hemochromatosis, a dominantly inherited disorder of iron metabolism. Multimers of ferroportin, whose existence may relate to the dominant inheritance pattern of disease, have been detected in some studies but not others. We looked for evidence of multimerization in several different types of experiment. We assayed the maturation of mutant and wild-type ferroportin and found that loss-of-function mutants had a reduced half-life but did not alter the stability of coexpressed wild-type. Using bioluminescence resonance energy transfer analysis, we tested how mature wild-type ferroportin behaved in intact live cell membranes. Ferroportin-ferroportin interactions gave the very low acceptor/donor ratio-independent energy transfer levels characteristic of random protein-protein interactions, consistent with ferroportin behaving as a monomer. Consistent with these experiments, we were unable to detect a dominant negative functional effect of mutant ferroportin on wild-type, even when expression of wild-type protein was titrated to low levels. These data suggest that dominantly inherited ferroportin disease does not result from the direct action of a mutated protein inhibiting a wild-type protein within multimers. We propose other possible mechanisms of disease.
Schimanski
Lisa M
LM
Molecular Immunology Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Oxford University, Oxford, UK OX3 9DS, UK. schimanski@hammer.imm.ox.ac.uk
Drakesmith
Hal
H
Talbott
Charlotte
C
Horne
Kerry
K
James
John R
JR
Davis
Simon J
SJ
Sweetland
Emma
E
Bastin
Judy
J
Cowley
Diana
D
Townsend
Alain R M
AR
D027682:Cation Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D005293:Ferritins / Q000378:metabolism*; D006432:Hemochromatosis / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D009154:Mutation; D000098742:Ferroportin
D027682:Cation Transport Proteins; D050505:Mutant Proteins; D000098742:Ferroportin; D005293:Ferritins