A transferrin-like protein that does not bind iron is induced by iron deficiency in the alga Dunaliella salina.
Iron deficiency induces two major transferrin-like proteins in the plasma membrane (Pm) of the halotolerant alga Dunaliella salina. TTf, a 150-kDa protein, previously identified as a salt-induced triplicated transferrin, having iron-binding characteristics resembling animal transferrins, and a 100-kDa protein designated idi-100 (for iron-deficiency-induced 100 kDa protein). According to the predicted amino acid sequence of idi-100, it is only 30% identical to TTf and differs from it in having two, rather than three, homologous internal repeats and in a lower conservation of canonical iron/bicarbonate binding residues. Both are localized in the outer surface of the membrane; however, TTf can be dissociated from the membrane by treatment with EDTA, whereas release of idi-100 requires detergents. The accumulation of idi-100 under iron deficiency lags behind that of TTf and in contrast to TTf, it is not induced by high salinity, suggesting that induction of idi-100 requires lower Fe threshold levels than that of TTf. In contrast to TTf, idi-100 does not bind Fe; however, there are indications for interactions with bicarbonate ions. These results suggest that despite their common resemblance to transferrins, their similar subcellular localization and their induction by iron deficiency, idi-100 and TTf fulfill different functions.
Schwarz
Michal
M
The Department of Biological Chemistry, Weizmann Institute of Science, PO Box 26, 76100 Rehovot, Israel.
Sal-Man
Neta
N
Zamir
Ada
A
Pick
Uri
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D000595:Amino Acid Sequence; D001483:Base Sequence; D001639:Bicarbonates; D002458:Cell Fractionation; D002462:Cell Membrane / Q000378:metabolism; D000460:Chlorophyta / Q000378:metabolism*; D003001:Cloning, Molecular; D004492:Edetic Acid; D005290:Ferric Compounds; D000090463:Iron Deficiencies; D008667:Metalloproteins / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014357:Trypsin
D001639:Bicarbonates; D005290:Ferric Compounds; D008667:Metalloproteins; C067440:LOC286987 protein, rat; D004492:Edetic Acid; D014357:Trypsin