Ferritins are ubiquitous proteins that serve the dual-function of iron reservoir and sequestering the Fe(II) toxicity. The function of ferritins totally depends on the characteristic spherical structure with a di-iron centre performing the iron oxidation and a hallow cavity enclosing the iron minerals in a bioavailable form. I have characterised the structure, assembly and function of a new member of ferritin superfamily that is natively enclosed within an encapsulin shell. Encapsulin proteins are structurally-related to a virus capsid and form 60-meric or 180-meric icosahedrons. I show that this encapsulin associated ferritin-like protein (EncFtn) possesses two main alpha helices, which assemble in a metal-dependent manner to form a ferroxidase centre at a dimer interface. EncFtn adopts an annular decamer structure in contrast to the 24-meric classical ferritins or 12-meric mini-ferritin (DPS). The resemblance of the dimeric EncFtn and monomeric classical ferritins suggests that it is likely that classical ferritin evolves from EncFtn because of the gene duplication. EncFtn is a catalytically active ferroxidase but with only a limited iron binding ability due to its open structure. The encapsulin itself is not able to oxidise Fe(II), but is able to store about 2200 iron ions. I have demonstrated that the EncFtn must be housed in the encapsulin to achieve a maximum loading of approximately 4200 iron ions. The encapsulin nanocompartments are widely-distributed in both eubacteria and archaeon with distinct life styles and represent a distinct class of iron storage system, where iron oxidation and mineralisation are distributed between two proteins.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:723881 |
| Date | January 2017 |
| Creators | He, Didi |
| Contributors | Bramham, Janice ; Walkinshaw, Malcolm |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/23466 |
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