Structural basis of ferroportin inhibition by minihepcidin PR73

[Research progress on iron metabolism in the occurrence and development of periodontitis]

Iron metabolism refers to the process of absorption, transport, excretion and storage of iron in organisms, including the biological activities of iron ions and iron-binding proteins in cells. Clinical research and animal experiments have shown that iron metabolism is associated with the progress of periodontitis. Iron metabolism not only enhances the proliferation and toxicity of periodontal pathogens, but also activate host immune-inflammatory response mediated by macrophages, neutrophils and lymphocytes. In addition, iron metabolism is also involved in regulating cellular death sensitivity of gingival fibroblasts and osteoblasts and promoting the differentiation of osteoclasts, which plays a regulatory role in the regeneration and repair of periodontal tissue. This article reviews the research progress on the pathogenesis of periodontitis from the perspective of iron metabolism, aiming to provide new ideas for the treatment of periodontitis.

In vitro reconstitution of transition metal transporters

Transition metal ions are critically important across all kingdoms of life. The chemical properties of iron, copper, zinc, manganese, cobalt, and nickel make them very attractive for use as cofactors in metalloenzymes and/or metalloproteins. Their versatile chemistry in aqueous solution enables them to function both as electron donors and acceptors, and thus participate in both reduction and oxidation reactions respectively. Transition metal ions can also function as nonredox multidentate coordination sites that play essential roles in macromolecular structure and function. Malfunction in transition metal transport and homeostasis has been linked to a wide number of human diseases including cancer, diabetes, and neurodegenerative disorders. Transition metal transporters are central players in the physiology of transition metals whereby they move transition metals in and out of cellular compartments. In this review, we provide a comprehensive overview of in vitro reconstitution of the activity of integral membrane transition metal transporters and discuss strategies that have been successfully implemented to overcome the challenges. We also discuss recent advances in our understanding of transition metal transport mechanisms and the techniques that are currently used to decipher the molecular basis of transport activities of these proteins. Deep mechanistic insights into transition metal transport systems will be essential to understand their malfunction in human diseases and target them for potential therapeutic strategies.

The mechanisms of ferroptosis and its role in atherosclerosis

Ferroptosis is a newly identified form of non-apoptotic programmed cell death, characterized by the iron-dependent accumulation of lethal lipid reactive oxygen species (ROS) and peroxidation of membrane polyunsaturated fatty acid phospholipids (PUFA-PLs). Ferroptosis is unique among other cell death modalities in many aspects. It is initiated by excessive oxidative damage due to iron overload and lipid peroxidation and compromised antioxidant defense systems, including the system Xc-/ glutathione (GSH)/glutathione peroxidase 4 (GPX4) pathway and the GPX4-independent pathways. In the past ten years, ferroptosis was reported to play a critical role in the pathogenesis of various cardiovascular diseases, e.g., atherosclerosis (AS), arrhythmia, heart failure, diabetic cardiomyopathy, and myocardial ischemia-reperfusion injury. Studies have identified dysfunctional iron metabolism and abnormal expression profiles of ferroptosis-related factors, including iron, GSH, GPX4, ferroportin (FPN), and SLC7A11 (xCT), as critical indicators for atherogenesis. Moreover, ferroptosis in plaque cells, i.e., vascular endothelial cell (VEC), macrophage, and vascular smooth muscle cell (VSMC), positively correlate with atherosclerotic plaque development. Many macromolecules, drugs, Chinese herbs, and food extracts can inhibit the atherogenic process by suppressing the ferroptosis of plaque cells. In contrast, some ferroptosis inducers have significant pro-atherogenic effects. However, the mechanisms through which ferroptosis affects the progression of AS still need to be well-known. This review summarizes the molecular mechanisms of ferroptosis and their emerging role in AS, aimed at providing novel, promising druggable targets for anti-AS therapy.

Structural insights into ferroportin mediated iron transport

Iron is a vital trace element for almost all organisms, and maintaining iron homeostasis is critical for human health. In mammals, the only known gatekeeper between intestinally absorbed iron and circulatory blood plasma is the membrane transporter ferroportin (Fpn). As such, dysfunction of Fpn or its regulation is a key driver of iron-related pathophysiology. This review focuses on discussing recent insights from high-resolution structural studies of the Fpn protein family. While these studies have unveiled crucial details of Fpn regulation and structural architecture, the associated functional studies have also at times provided conflicting data provoking more questions than answers. Here, we summarize key findings and illuminate important remaining questions and contradictions.

Genetic Incorporation of Dansylalanine in Human Ferroportin to Probe the Alternating Access Mechanism of Iron Transport

Ferroportin (Fpn), a member of the major facilitator superfamily (MFS) of transporters, is the only known iron exporter found in mammals and plays a crucial role in regulating cellular and systemic iron levels. MFSs take on different conformational states during the transport cycle: inward open, occluded, and outward open. However, the precise molecular mechanism of iron translocation by Fpn remains unclear, with conflicting data proposing different models. In this work, amber codon suppression was employed to introduce dansylalanine (DA), an environment-sensitive fluorescent amino acid, into specific positions of human Fpn (V46, Y54, V161, Y331) predicted to undergo major conformational changes during metal translocation. The results obtained indicate that different mutants exhibit distinct fluorescence spectra depending on the position of the fluorophore within the Fpn structure, suggesting that different local environments can be probed. Cobalt titration experiments revealed fluorescence quenching and blue-shifts of λmax in Y54DA, V161DA, and Y331DA, while V46DA exhibited increased fluorescence and blue-shift of λmax. These observations suggest metal-induced conformational transitions, interpreted in terms of shifts from an outward-open to an occluded conformation. Our study highlights the potential of genetically incorporating DA into Fpn, enabling the investigation of conformational changes using fluorescence spectroscopy. This approach holds great promise for the study of the alternating access mechanism of Fpn and advancing our understanding of the molecular basis of iron transport.

Mechanism of Ca2+ transport by ferroportin

Ferroportin (Fpn) is a transporter that releases ferrous ion (Fe²⁺) from cells and is important for homeostasis of iron in circulation. Export of one Fe²⁺ by Fpn is coupled to import of two H⁺ to maintain charge balance. Here, we show that human Fpn (HsFpn) binds to and mediates Ca²⁺ transport. We determine the structure of Ca²⁺-bound HsFpn and identify a single Ca²⁺ binding site distinct from the Fe²⁺ binding sites. Further studies validate the Ca²⁺ binding site and show that Ca²⁺ transport is not coupled to transport of another ion. In addition, Ca²⁺ transport is significantly inhibited in the presence of Fe²⁺ but not vice versa. Function of Fpn as a Ca²⁺ uniporter may allow regulation of iron homeostasis by Ca²⁺.