Comparative Analysis of Some Fungal Ferritins Belonging to Microsporidia & Ascomycota

Author Name(s): *Swathi. K ,Hymavathi CH ,Janardhan .K
Author Email: k.swti1988@gmail.com

Abstract

Iron is an extremely important element whose function is involved in the oxygen transport and it participates in the electron transfer reactions and various redox potential reactions. Ferritin, the globular cytoplasmic protein is highly conserved and is involved in the regulation of the flow of iron into and out of the cell. Ferritins play a key role in preventing Fe toxicity because of their ability to sequester several thousand Fe atoms in their central cavity in soluble, nontoxic bioavailable form. The structural integrity of the protein makes it convenient to store 45,000 molecules of iron in it. In this paper we have worked on the analysis of ferritin from different species of Fungi using bioinformatics tools. By these tools it was found that the myco ferritin of fungi belonging to the same species was closely related and is highly conserved.

Keywords:

Iron, Ferritin, Electron transfer reactions, Redox Potential, MycoFerritin.

Introduction

Iron is a key element for the growth and development of any cell or organism. Eukaryotic cells, entering the S-phase of the cell cycle, up regulate transferring receptor-1 expression to obtain iron from the extracellular environment. Iron is a co-factor ribonucleotidereductase, which is necessary for DNA synthesis, and of oxygen transporters in mitochondria, and activates the cyclin/cyclin-dependent kinase complexes, thus regulating the progression from the G1- phase to the S-phase of the cell cycle [1] Anytime iron exceeds the metabolic needs of the cell it may form a low molecular weight pool, referred to as the Labile Iron Pool (LIP), which catalyzes the conversion of normal by- products of cell respiration, like superoxide anion (O₂⁻) and hydrogenperoxide (H₂O₂), into highly damaging hydroxyl radical(HO.)[2].
The highly reactive hydroxyl radical (HO*) generated from an interaction between superoxide (O₂._) and hydrogen peroxide (H₂O₂) was proposed (with Joseph Weiss) in Professor Haber’s final paper.
[Haber–Weiss reaction (commonly referred to as the iron-catalysed Haber–Weiss reaction)] [3] O₂ + H₂O₂ HO* + O₂ +OH⁻
Iron is toxic in uncontained situations because it catalyzes the production of free radical. Thus iron in the cell is stored in “FERRITIN”.
Ferritin, the iron storage protein (450 kDa), plays a dynamic role in iron metabolism by sequestering toxic free iron [4] Structurally, it consists of a central ferric hydroxy phosphate core surrounded by an outer protective protein shell called Apo ferritin. The iron content of the core ranges from 0 to 4500 iron atoms per molecule and is a reflection of somatic iron reserves [5] Ferritin, the globular cytoplasmic iron storage protein is highly conserved. Ferritin is a protein of 24 peptide subunits assembled into a hollow shell of molecular weight 4,74,000g/mol (Briatet al., 1999). In iron rich conditions ferritin acts as iron sequestering protein, protecting cells against iron toxicity and at low iron conditions it acts as a source of iron ions necessary for iron-containing protein synthesis. However, the physiological mechanism of iron release from ferritin remains obscure. Apo ferritin part of Ferritin binds to the free ferrous iron and stores it in the ferric state i.e. catalyzes the oxidation of Fe2+ to Fe3+state. The central core of the ferritin has a ferroxidase activity. Oxidation at specific site on the protein is involved in the initial phase of core formation, it is generally accepted that once a critical nucleus of Fe3+ ions has been formed, and has begun to hydrolyze, it will then act in an autocatalytic manner to promote crystal growth on the surface of the initial biomineral core.
Among different members of Fungi 3 different types of Ferritin’s were found. And the three types of ferritins that have been described were
(i) Mycoferritin, which resembles mammalian ferritins; [6] (ii) Zygoferritin,a unique form of ferritin found only in the zygomycetes; [7] (iii) A Bacterioferritin found in Absidia spinosa [8] Under conditions of extreme iron stress, fungi produce low molecular- weight (Molwt, 1,500) ferric iron chelators known collectively as siderophores. Most of the fungal siderophores are hydroxamates. However, the zygomycetes form iron-regulated polycarboxylates and these are well documented.

Conclusion

Ferritin is a molecule which acts as buffer in controlling the flow of Iron in the cell. In case of Fungi the, MycoFerritin plays an important role in the normal growth of the cells and for its pathogenicity. It has been found that Myco Ferritins are highly localized in cytoplasm and a little amount of it is present in the mitochondria (refer table 2). The domain region in all the above selected MycoFerritinis was found to start with similar amino acid and was found to be of similar length with respect to domain. The iron storing capacity of the MycoFerritin is because of its structural integrity. The alpha helix conformation of the protein is central criteria for the molecule to store 24000 iron molecules in it. It was found that the mycoferritin is highly conserved among the species of the same phylum i.e. the fungi of Ascomycota as compared to the Mycoferritin of species of Microsporidia. Thus by this we can say that the ferritin is functionally conserved among and between the phyla of fungi.

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