Poster Presentation The 47th Lorne Conference on Protein Structure and Function 2022

Structural insights into the ferroxidase and iron sequestration mechanisms of ferritin from Caenorhabditis elegans (#232)

Tess R Malcolm 1 , Sanjeedha Mubarak 1 , Hamish G Brown 2 , Eric Hanssen 2 , Gawain McColl 3 , Guy NL Jameson 1 , Megan J Maher 1
  1. Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, VICTORIA, Australia
  2. Ian Holmes Imaging Centre, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria, Australia
  3. The Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia

Iron is an essential trace element required for a multitude of cellular processes, that when in excess, becomes toxic [1]. Strict regulation of iron concentrations is therefore paramount to cellular health [2]. Ferritin is a ubiquitous iron-storage protein that forms a highly conserved 24-subunit spherical cage-like structure. Ferritin catalyses the oxidation of iron and storage as a mineral core within the cage-like structure to prevent cellular damage [3]. Although ferritin has been extensively investigated, the mechanistic details of iron uptake, oxidisation and transfer to the core remain divisive. In this study, we utilise the model organism, Caenorhabditis elegans, to investigate these processes.

C. elegans contains two ferritin proteins, FTN-1 and FTN-2, that are orthologous to the two human ferritins [4]. FTN-1 and FTN-2 appear to function as a ‘hybrid’ of HuLF and HuHF, with both proteins facilitating iron core nucleation and exhibiting ferroxidase activity. Although highly conserved in both the nucleation and ferroxidase centres, the processes of nucleation and oxidation occur faster in FTN-2 than FTN-1. To understand the structural basis of this, the X-ray crystal structures of FTN-1 and FNT-2 were resolved. Both FTN-1 and FTN-2 exhibited the conserved 24-mer cage-like structure and coordinated one iron in the ferroxidase centre of each chain. Comparison of the structures suggest FTN-2 may possess a more favourable pathway to the ferroxidase centre than FTN-1, in addition to a potential nucleation centre with higher nucleation capacity. To map the pathway from iron entry to the ferroxidase centre and the mineral core, we resolved FTN-2 in the presence of iron at increasing time points. Iron coordination varied within FTN-2 depending on exposure time, providing a basis for further experiments investigating this pathway.

These structural insights will further our understanding of the mechanisms ferritins utilise to regulate iron storage within the iron homeostasis network.  

 

 

  1. [1] Anderson, G.J. & Frazer, D.M. (2017). Am. J. Clin. Nutr. 106, 1559S-1566S.
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  3. [3] Ebrahimi, K.H., Hagedoorn, P. & Hagen, W.R. (2015). Chem Rev. 115 (1), 295-326.
  4. [4] Anderson, C.P. & Leibold, E.A. (2014). Front Pharmacol. 5 (113).