The Iron-Thiol-Oxygen Nexus for Iron Flux from Bare and Ferritin-caged Mineral and Safeguarding DNA: Impact of Thiol Structure and Protein Coat

Abstract

The interplay between iron-sulfur-oxygen underpins the redox regulation of iron across biological and geochemical systems. Prior to the Great Oxygenation Event (GOE), sulfur fostered a reducing environment essential for Fe2+ bioavailability. Post-GOE, advent of oxidative-environment depleted iron-bioavailability likely spurred the evolution of ferritin, a nanocage protein that detoxifies Fe2+ and catalytically synthesizes ferrihydrite bio-mineral. Biological iron usage necessitates its reduction and mobilization from bio-mineral, where thiols can play a critical role as electron donors. This study probes the efficacy of various cellular and synthetic thiols in mediating Fe3+/Fe2+ redox-cycling, O2 consumption, and the dissolution/mobilization of iron mineral from bare and ferritin protein-encapsulated ferrihydrite to correlate its structure-activity relationship. Furthermore, antioxidative properties were assessed through DNA protection and radical scavenging assays. This work reports the formation of thiol-specific transient species upon interaction with Fe3+ and exhibits synergistic O2 consumption, rapidly generating a hypoxic microenvironment. The thiol-mediated iron mobilization is influenced by: mineral accessibility/size (Na2S/TG vs GSH), O2 consumption ability and iron chelating feature (-SH/-COO‒ vs -NH3+: TG/DHLA vs Cys/GSH), highlighting entropic contributions (higher efficacy of dithiols over monothiol: DTT/DHLA vs 2-ME) and restriction posed by protein encapsulation (bare > encapsulated). Inclusion of ferritin cage-variants, offers a perspective on evolutionary upgradation of protein coat, showing how the stability of a mineral core is governed by the specific design of its inorganic-protein interface. These findings underscore the crucial role of cooperativity among iron-sulfur-oxygen interactions in cellular homeostasis providing quintessential insights into therapeutic strategies for regulating iron metabolism and oxidative stress mitigation.