title: A Diatom Ferritin Optimized for Iron Oxidation but Not Iron Storage.
abstract: Ferritin from the marine pennate diatom Pseudo-nitzschia multiseries (PmFTN) plays a key role in sustaining growth in iron-limited ocean environments. The di-iron catalytic ferroxidase center of PmFTN (sites A and B) has a nearby third iron site (site C) in an arrangement typically observed in prokaryotic ferritins. Here we demonstrate that Glu-44, a site C ligand, and Glu-130, a residue that bridges iron bound at sites B and C, limit the rate of post-oxidation reorganization of iron coordination and the rate at which Fe(3+) exits the ferroxidase center for storage within the mineral core. The latter, in particular, severely limits the overall rate of iron mineralization. Thus, the diatom ferritin is optimized for initial Fe(2+) oxidation but not for mineralization, pointing to a role for this protein in buffering iron availability and facilitating iron-sparing rather than only long-term iron storage.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Pfaffen
authors.affiliation: Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Bradley
authors.affiliation: Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
authors.forename: Raz
authors.initials: R
authors.lastname: Abdulqadir
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Marlo R
authors.initials: MR
authors.lastname: Firme
authors.affiliation: Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
authors.forename: Geoffrey R
authors.initials: GR
authors.lastname: Moore
authors.affiliation: Centre for Molecular and Structural Biochemistry, School of Chemistry, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom. Electronic address: n.le-brun@uea.ac.uk.
authors.forename: Nick E
authors.initials: NE
authors.lastname: Le Brun
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.
authors.forename: Michael E P
authors.initials: MEP
authors.lastname: Murphy
mesh_terms: D002384:Catalysis; D003001:Cloning, Molecular; D017377:Diatoms / Q000378:metabolism*; D005293:Ferritins / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D005293:Ferritins; D007501:Iron
keywords: algae; enzyme kinetics; ferritin; ferroxidase center; iron; iron storage mechanism; protein structure; x-ray crystallography