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Cloning and characterization of a novel ferritin from the marine diatom Pseudo-nitzschia multiseries Moccia, Lauren Paul
Abstract
Diatoms play a fundamental role in marine food webs, and significantly contribute to global primary production and carbon sequestration into the deep ocean. In many offshore areas of the open ocean, iron (Fe) input is low, and its availability often limits phytoplankton biomass. Recently, gene sequences encoding ferritin, a nearly ubiquitous iron storage and detoxifying protein, have been identified in pennate diatoms such as Pseudo-nitzschia, but not in other Stramenopiles (which include centric diatoms, brown algae and some protist plant parasites) or Cryptophyte relatives. Members of this genus readily bloom upon addition of iron to Fe-limited waters, and are known to produce the neurotoxin domoic acid. Until now, the reason for the success of pennate diatoms in the open ocean was uncertain; however, expressing ferritin would allow pennate species to store Fe after a transient input, using it to dominate Fe stimulated algal blooms. Here, the ferritin gene was cloned from the coastal pennate diatom Pseudonitzschia multiseries, overexpressed in Escherichia coli, and purified using liquid chromatography. The ferritin protein sequence appears to encode a non-heme, ferritinlike di-iron carboxylate protein, while gel filtration chromatography and SDS-PAGE indicate that this ferritin is part of the 24 subunit maxi-ferritins. Spectroscopically monitoring the addition of Fe(II) to a buffered ferritin solution shows that the P. multiseries protein demonstrates ferroxidase activity, binding iron and storing it as Fe(III) in excess of 600 equivalents per protein shell. In keeping with the typical stoichiometry of the ferroxidase reaction, oxygen (O₂) is consumed in a 2 Fe:O₂ratio while hydrogen peroxide is produced concurrently. iii Diatoms evolved from secondary endosymbiosis involving eukaryotic red algae; however, a broad phylogenetic comparison suggests that P. multiseries ferritin was likely acquired via lateral gene transfer from cyanobacteria – not from its ancestral endosymbionts. Until recently, no other ferritins have been identified in diatoms, and the protein characterized here is unique in that it seems to be derived from a prokaryotic organism yet it occurs in a marine eukaryote. These findings have direct implications for the success of pennate diatoms in both Fe rich coastal waters and upon Fe addition in the open ocean.
Item Metadata
Title |
Cloning and characterization of a novel ferritin from the marine diatom Pseudo-nitzschia multiseries
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
2008
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Description |
Diatoms play a fundamental role in marine food webs, and significantly
contribute to global primary production and carbon sequestration into the deep ocean. In
many offshore areas of the open ocean, iron (Fe) input is low, and its availability often
limits phytoplankton biomass. Recently, gene sequences encoding ferritin, a nearly
ubiquitous iron storage and detoxifying protein, have been identified in pennate diatoms
such as Pseudo-nitzschia, but not in other Stramenopiles (which include centric diatoms,
brown algae and some protist plant parasites) or Cryptophyte relatives. Members of this
genus readily bloom upon addition of iron to Fe-limited waters, and are known to
produce the neurotoxin domoic acid. Until now, the reason for the success of pennate
diatoms in the open ocean was uncertain; however, expressing ferritin would allow
pennate species to store Fe after a transient input, using it to dominate Fe stimulated algal
blooms.
Here, the ferritin gene was cloned from the coastal pennate diatom Pseudonitzschia
multiseries, overexpressed in Escherichia coli, and purified using liquid
chromatography. The ferritin protein sequence appears to encode a non-heme, ferritinlike
di-iron carboxylate protein, while gel filtration chromatography and SDS-PAGE
indicate that this ferritin is part of the 24 subunit maxi-ferritins. Spectroscopically
monitoring the addition of Fe(II) to a buffered ferritin solution shows that the P.
multiseries protein demonstrates ferroxidase activity, binding iron and storing it as Fe(III)
in excess of 600 equivalents per protein shell. In keeping with the typical stoichiometry
of the ferroxidase reaction, oxygen (O₂) is consumed in a 2 Fe:O₂ratio while hydrogen
peroxide is produced concurrently.
iii
Diatoms evolved from secondary endosymbiosis involving eukaryotic red algae;
however, a broad phylogenetic comparison suggests that P. multiseries ferritin was likely
acquired via lateral gene transfer from cyanobacteria – not from its ancestral
endosymbionts. Until recently, no other ferritins have been identified in diatoms, and the
protein characterized here is unique in that it seems to be derived from a
prokaryotic organism yet it occurs in a marine eukaryote. These findings have direct
implications for the success of pennate diatoms in both Fe rich coastal waters and
upon Fe addition in the open ocean.
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Extent |
3224211 bytes
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Subject | |
Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2008-06-25
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Provider |
Vancouver : University of British Columbia Library
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Rights |
Attribution-NonCommercial-NoDerivatives 4.0 International
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DOI |
10.14288/1.0052359
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
2008-11
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Campus | |
Scholarly Level |
Graduate
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Rights URI | |
Aggregated Source Repository |
DSpace
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Rights
Attribution-NonCommercial-NoDerivatives 4.0 International