Comparative Analysis of Some Algal Ferritins Belonging To Chlorophyta and Rhodophyta

Author Name(s): Sana Raoof, Bhavani.V, Nagalakshmi.T, Ashwini.M, G. Uma Sree,* Janardhan.K
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Ferritin is the most important protein involved in the Iron metabolism and storage. 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. The structural integrity of the protein makes it convenient to store 45,000 molecules of iron in it. In the current paper we have worked on the analysis of ferritin from different species of Algae using bioinformatics tools. Algal ferritins studies are undertaken with reference to some of the members of Chlorophyta and Rhodophyta. Chlamydomonas reinhardtii is a model member of Chlorophyta involving two unlinked genes FER1 and FER2 encoding ferritin sub-units. Comparative studies are performed in different classes of algae i.e. Chlorophyta and Rhodophyta to understand variations in ferritin sequences.


Ferritin, Electron Transfer, Chlorophyta, Rhodophyta, FER1 and FER2.


Metal interactions with organic compounds are numerous in all living organisms. They are essential for many biochemical processes occurring within cells, and concern not only metabolism, but also some regulatory mechanisms of gene expression. Among metals, iron is of special interest because it is required in most of the cellular redox reactions and it is one of the major metals involved in electron transfer chains. However, its strong reactivity with oxygen makes it a difficult element to handle by aerobic organisms. Indeed, both its insolubility in the form of ferric hydroxides, or its toxicity through the Fenton reaction producing hydroxyl radicals (which are among the most chemically reactive species), have introduced evolutionary constraints in order to enable this metal to be safely utilized by living organisms [1]. The narrow efficient iron concentration required for cellular needs is strictly controlled by biological processes acting both at the transport and the storage levels. In multicellular organisms, transport mechanisms regulate iron traffic from uptake to long distance tissular distribution, and ultimately to subcellular allocation [2]. Although the structure of ferritins is highly conserved between plants and animals, their cellular localization differs. Furthermore, regulation of ferritin gene expression in response to iron excess occurs at the transcriptional level in plants, in contrast to animals which regulate ferritin expression at the translational level.
Iron is toxic in uncontained situations because it catalyzes the production of free radical. Thus iron in the cell is stored in “FERRITIN” [10].
In algae, ferritins are plastid-located proteins able to form a holosphere, which can contain up to 4500 Fe atoms. This process allows us to buffer free iron, making it available under a safe form, and reveals a key role for ferritin in iron homeostasis and protection against iron-mediated oxidative stress [4]. Pre-ferritin, with a plastid targeting sequence, is encoded by a multigene family in plants. Increased ferritin production in high-iron-supplied cells is accomplished, at least in part, by transcriptional regulation of one or more ferritin genes [5]. This pattern of expression is consistent with a role for ferritin as an iron storage molecule under conditions of iron overload[6]. Despite extensive studies conducted during the last decade, many factors regulating the expression of ferritin genes in plants remain unknown (Marek Figlerowicz, 2009).
Ferritins are a broad superfamily of iron storage proteins, found in all the living kingdom, except in yeast (Andrews et al., 2003; Briat et al., 2006; Arosio et al., 2008).
Three subclasses of these proteins can be defined:
(1) haem-free ferritins present both in pro- and eukaryotes;
(2) haem-containing bacterioferritins, found only in bacteria; and
(3) DNA binding proteins from starved cells (Dps), called miniferritins,
Present in prokaryotes (Smith, 2004). Ferritins and bacterioferritins are composed of 24 subunits whereas only 12 identical subunits form the Dps proteins. These subunits assemble in a spherical protein shell defining a central cavity able to
accommodate between 2000 and 4000 ferric iron atoms for ferritins and 500 atoms for miniferritins [3].
Chlamydomonas model. Significant insights into plant metal metabolism can be gained from studying other model photosynthetic organisms such as the unicellular green alga Chlamydomonasreinhardtii. With its simple growth requirements C. reinhardtii is a valuable experimental model for the study of metalloprotein biosynthesis and metal-responsive gene regulation in photosynthetic organisms. While efficient transport mechanisms for iron uptake are an essential element in all pro- and eukaryotic cells, its intracellular availability and storage have to be tightly regulated, not only to buffer supply and demand, but also to prevent cell damage from undesirable reactions of free radicals, formed catalytically by free Fe ions. Ferritin represents the most common form of iron storage in all domains of life [2].


Ferritin has long been known as an iron storage protein. In the present investigation using different bioinformatics tools (ProtParam, PROSITE, GOR, NetNes, ClustalW) we have tried to analyze which amino acid is present in abundance, which amino acid is playing role in the protein export and functional activity and also the genetic relatedness among these selected organisms. From the results obtained it is concluded that among the 6 different members of Chlorophyta and Rhodophyta selected for the comparative analysis of ferritin, the amino acid Alanine was found to be present in highest frequency and Alanine and Leucine together might be performing the protein export function. Glutamic acid is the amino acid found to be playing role in the functional activity of the protein in most of them. The dendrogram revealed that Ostreococcus tauri is genetically diverse from the other organisms selected for the analysis.

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