title: A multicopper ferroxidase involved in iron binding to transferrins in Dunaliella salina plasma membranes.
abstract: The halotolerant alga Dunaliella salina is unique among plants in that it utilizes a transferrin (TTf) to mediate iron acquisition (Fisher, M., Zamir, A., and Pick, U. (1998) J. Biol. Chem. 273, 17553-17558). Two new proteins that are induced by iron deprivation were identified in plasma membranes of D. salina as follows: a multicopper ferroxidase termed D-Fox and an internally duplicated glycoprotein (p130B). D-Fox and p130B are accessible to glycolytic, proteolytic, and biotin surface tagging treatments, suggesting that they are surface-exposed glycoproteins. Induction of D-Fox was also manifested by ferroxidase activity in plasma membrane preparations. These results are puzzling because ferroxidases in yeast and in Chlamydomonas reinhardtii function in redox-mediated iron uptake, a mechanism that is not known to operate in D. salina. Two lines of evidence suggest that D-Fox and p130B interact with D. salina triplicated transferrin (TTf). First, chemical cross-linking combined with mass spectroscopy analysis showed that D-Fox and p130B associate with TTf and with another plasma membrane transferrin. Second, detergent-solubilized D-Fox and p130B comigrated on blue native gels with plasma membrane transferrins. 59Fe autoradiography indicated that this complex binds Fe3+ ions. Also, the induction of D-Fox and p130B is kinetically correlated with enhanced iron binding and uptake activities. These results suggest that D-Fox and p130B associate with plasma membrane transferrins forming a complex that enhances iron binding and iron uptake. We propose that the function of D-Fox in D. salina has been modified during evolution from redox-mediated to transferrin-mediated iron uptake, following a gene transfer event of transferrins from an ancestral animal cell.
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Yakov
authors.initials: Y
authors.lastname: Paz
authors.forename: Adriana
authors.initials: A
authors.lastname: Katz
authors.forename: Uri
authors.initials: U
authors.lastname: Pick
mesh_terms: D020418:Algal Proteins / Q000235:genetics* / Q000502:physiology; D000595:Amino Acid Sequence; D001345:Autoradiography; D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism*; D002570:Ceruloplasmin / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D003001:Cloning, Molecular; D003432:Cross-Linking Reagents / Q000494:pharmacology; D056890:Eukaryota / Q000378:metabolism*; D007501:Iron / Q000737:chemistry*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000378:metabolism; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D014168:Transferrin / Q000737:chemistry*
chemical_list: D020418:Algal Proteins; D003432:Cross-Linking Reagents; D014168:Transferrin; D007501:Iron; D002570:Ceruloplasmin; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase