SSRL Science Highlight - June 2009 | ||||||||||||
Almost all organisms require iron as a co-factor in numerous metalloproteins
and enzymes. In particular, phytoplankton, which are aquatic, free-drifting,
single-celled organisms that can harvest energy from the sun, have an elevated
demand for iron due to the large role it plays in their photosynthetic
machinery. In 30-40% of the world's oceans iron concentrations are low enough
to limit the growth of phytoplankton (Martin and Fitzwater 1988; Moore et al.
2002). New sources of iron to these regions are sporadic and typically
include atmospheric dust deposition or weak upwelling of deep waters.
Data collected at SSRL Beam Lines 9.2, 7.1 and at the Canadian Light Source
allowed the determination of crystal structures of recombinant ferritin from
the marine pennate diatom, Pseudo-nitzschia multiseries (Figure 1). This
pennate diatom ferritin forms an assembly of 24 monomers forming a hollow
sphere with a diameter of approximately 120 Å, typical of the ferritin
family (Figure 2A). In plants and animals, ferritin stores up to 4500 iron
atoms as an iron oxide mineral and can release it on cellular demand (Liu and
Theil 2005). Cells thereby are protected from potential oxidative damage
resulting from the interaction of iron with reactive oxygen. Iron atoms are
bound at the ferroxidase centers where ferrous iron is oxidized by oxygen
(Figure 2B). The ferroxidase site has unique features suggesting that catalytic
activity is tuned for the specific needs of the diatom. Additional iron atoms
were found to trail from the ferroxidase center towards the hollow center of
the ferritin sphere where mineralization and storage of iron occurs.
This research was supported by a Gordon and Betty Moore Foundation Marine
Microbiology Investigator Award, a National Science Foundation grant, a
National Institute of Environmental Health Sciences grant, a National Sciences
and Engineering Research Council of Canada grant and a Canadian Institutes of
Health Research grant. Portions of this research were carried out at the
Canadian Light Source and the SSRL. The SSRL Structural Molecular Biology
Program is supported by the Department of Energy, Office of Biological and
Environmental Research, and by the National Institutes of Health, National
Center for Research Resources, Biomedical Technology Program, and the National
Institute of General Medical Sciences.
Primary Citation
Marchetti A., Parker M.S., Moccia L.P., Lin E.O., Arrieta A.L., Ribalet F.,
Murphy M.E.P., Maldonado M.T., Armbrust E.V. (2009) Ferritin is used for iron
storage in bloom-forming marine pennate diatoms. Nature, 457, 467-470.
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SSRL is supported by the Department of Energy, Office of Basic Energy Sciences. The SSRL Structural Molecular Biology Program is supported by the Department of Energy, Office of Biological and Environmental Research, and by the National Institutes of Health, National Center for Research Resources, Biomedical Technology Program, and the National Institute of General Medical Sciences. |
Last Updated: | 16 June 2009 |
Content Owner: | A. Marchetti, University of Washington |
Page Editor: | L. Dunn |