Iron redox pathway revealed in ferritin via electron transfer analysis

Abstract

ferritin protein is involved in biological tissues in the storage and management of iron -an essential micro-nutrient in the majority of living systems. While there are extensive studies on iron-loaded ferritin, its functionality in iron delivery is not completely clear. Here, for the first time, differential pulse voltammetry (DpV) has been successfully adapted to address the challenge of resolving a cascade of fast and co-occurring redox steps in enzymatic systems such as ferritin. Using DpV, comparative analysis of ferritins from two evolutionary-distant organisms has allowed us to propose a stepwise resolution for the complex mix of concurrent redox steps that is inherent to ferritins and to fine-tune the structure-function relationship of each redox step. indeed, the cyclic conversion between fe 3+ and fe 2+ as well as the different oxidative steps of the various ferroxidase centers already known in ferritins were successfully discriminated, bringing new evidence that both the 3-fold and 4-fold channels can be functional in ferritin.Ferritin is an ubiquitous protein 1,2 involved in the storage and management of iron -an essential micro-nutrient for almost all living systems. The protein occurs in abundance in the cytosol and mitochondria, where it helps maintaining the performance of critical biochemical reactions 3-6 and balance oxidative stress processes 7 . Ferritin is therefore mainly internal in most systems, but can sometimes be a secreted enzyme 7 , and can thus be used to manage balance of iron both intra-and extracellularly, which can protect from deleterious excess of iron uptake, but also from viral and bacterial infections. Ferritin is known to take up iron (as Fe 2+ ) and store it in stable unreactive Fe 3+ -oxide/hydroxide form (primarily ferrihydrite). It is believed to deliver Fe back in a functional Fe 2+ form, where and when needed for biological processes 8 . In spite of many biochemical studies on performance of loaded ferritin, some parts of the molecular mechanisms of iron uptake, e.g., associated with oxidation steps, and most of the iron release and delivery, e.g., associated with reduction steps), remain largely unclear and speculative [8][9][10][11] .Structurally, ferritin is a biomacropolymeric enzyme constituted of 24 subunits (Fig. 1a,b) forming a hollow structure -often referred to as a cage that can be loaded 12 with Fe. The cage has an octahedral (432) symmetry where the 4-fold and 3-fold axes of symmetry are the place where 4 and 3 subunits meet together to respectively delineate six four-fold channels and eight three-fold channels. These channels have a small diameter (ranging from ~0.2 nm to ~0.5 nm) that varies along the 3 -4 nm length of the channels. To date both the 3-fold and 4-fold channels have been considered for the Fe 2+ ion entry into the core of the cage, but proof of natural activity 8,11,13 has been delivered only for the 3-fold channels. There are three types of ferritin subunits: Light (L), a Middle (M) and a Heavy (H) subunit, in increasing order of molecul...

Ultra-sensitive viral glycoprotein detection NanoSystem toward accurate tracing SARS-CoV-2 in biological/non-biological media

“…Since the CV method has several limitations due to its inherent low resolution and low sensitivity, it is favored to use DPV as a more sensitive voltammetric method along with a higher resolution for this aim. Thereby, better diagnostic criteria was obtained by DPV analysis in order to distinguish different types of electrode mechanisms ( Chen et al, 2020 ; Kim et al, 2003 ). In this case, to probe the redox mechanism of functional groups present on viral glycoproteins, the anodic and cathodic peak currents related to the DPV pattern of SARS-CoV-2 are carefully analyzed.…”

Structural Insights Into the Effects of Interactions With Iron and Copper Ions on Ferritin From the Blood Clam Tegillarca granosa

“…For TgFer and TgFer + Fe, the free iron ions outside of ferritin can be attracted by the His116 and Asp120 residues located at the entrance of the 3-fold channel, then guided into the 3-fold pore, where they interact with the side chains of Asp129 and Glu132 residues, as illustrated in Figures 5A,B , indicating the crucial role played by the unique electrostatic arrangement of the 3-fold channel in iron transportation ( Maity et al, 2019 ). It has been proposed that the Fe 2+ ion located at the deepest part of the channel pore can travel toward the ferroxidase center with the help of amino acid residue ( Chen et al, 2020 ). In TgFer + CuFe, two Cu 2+ ions were tightly coordinated with the Asp129 and Glu132 residues of the 3-fold pore, similar to the structure of TgFer + Cu, and the Cu-Cu distance was approximately 4.5 Å and 3.9 Å, respectively ( Figure 5D and Supplementary Figure S3 ).…”

Structural Rearrangement of Dps-DNA Complex Caused by Divalent Mg and Fe Cations

“…Unique metal-binding sites locate both on the external surface of the dodecamer and within the hollow cavity in the middle of the Dps dodecamer. These metal-binding sites of ferritin-like proteins, as a rule, are rich in Asp, His and Glu amino acids [ 13 , 14 , 24 , 29 , 30 , 31 ]; however, the sites are not highly conserved and the amino acids within them can be replaced by Lys, Ala and others.…”