Structural features determining the vitamin K epoxide reduction activity in the VKOR family of membrane oxidoreductases

Inhibition of FSP1: A new strategy for the treatment of tumors (Review)

Ferroptosis, a regulated form of cell death, is intricately linked to iron‑dependent lipid peroxidation. Recent evidence strongly supports the induction of ferroptosis as a promising strategy for treating cancers resistant to conventional therapies. A key player in ferroptosis regulation is ferroptosis suppressor protein 1 (FSP1), which promotes cancer cell resistance by promoting the production of the antioxidant form of coenzyme Q10. Of note, FSP1 confers resistance to ferroptosis independently of the glutathione (GSH) and glutathione peroxidase‑4 pathway. Therefore, targeting FSP1 to weaken its inhibition of ferroptosis may be a viable strategy for treating refractory cancer. This review aims to clarify the molecular mechanisms underlying ferroptosis, the specific pathway by which FSP1 suppresses ferroptosis and the effect of FSP1 inhibitors on cancer cells.

Vitamin K Epoxide Reductase Complex-Protein Disulphide Isomerase Assemblies in the Thiol-Disulphide Exchange Reactions: Portrayal of Precursor-to-Successor Complexes

The human Vitamin K Epoxide Reductase Complex (hVKORC1), a key enzyme that converts vitamin K into the form necessary for blood clotting, requires for its activation the reducing equivalents supplied by its redox partner through thiol-disulphide exchange reactions. The functionally related molecular complexes assembled during this process have never been described, except for a proposed de novo model of a 'precursor' complex of hVKORC1 associated with protein disulphide isomerase (PDI). Using numerical approaches (in silico modelling and molecular dynamics simulation), we generated alternative 3D models for each molecular complex bonded either covalently or non-covalently. These models differ in the orientation of the PDI relative to hVKORC1 and in the cysteine residue involved in forming protein-protein disulphide bonds. Based on a comparative analysis of these models' shape, folding, and conformational dynamics, the most probable putative complexes, mimicking the 'precursor', 'intermediate', and 'successor' states, were suggested. In addition, we propose using these complexes to develop the 'allo-network drugs' necessary for treating blood diseases.

Design of a structure-activity relationship model of vitamin K epoxide reductase (VKORC1) inhibitors combining chemical synthesis of new compounds, enzymatic assays and molecular modelling

Vitamin K antagonists (VKAs) anticoagulants have been used since the 1950s as medicines and rodenticides. These molecules are mainly 4-hydroxycoumarin derivatives and act by inhibiting the vitamin K epoxide reductase (VKORC1), an endoplasmic reticulum membrane resident enzyme. However, many VKORC1 mutations have been reported over the last decade, inducing VKAs resistances and thus treatments failures. Although studies have reported experimental and computational investigations of VKAs based on VKORC1 structural homology models, the development of new effective anticoagulants has been quite complex due to the lack of structural data and reliable structure-activity relationships. However, the recent publication of VKORC1 crystal structure provides new information for further studies. Based on these findings, we combined chemical synthesis, enzymatic assays and molecular modelling methods to design a structure-activity relationship (SAR) model. Our results proved that the lipophilicity, the membrane permeability of inhibitors and their affinity towards human VKORC1 enzyme are the main characteristics for potent anticoagulants. Our SAR model managed to rank compounds according to their ability to inhibit the human VKORC1. Such a tool might constitute an alternative to evaluate new molecules potency before their chemical synthesis and biological assessment and might assist the development of new VKAs.

Distinct enzymatic strategies for de novo generation of disulfide bonds in membranes

Disulfide bond formation is a catalyzed reaction essential for the folding and stability of proteins in the secretory pathway. In prokaryotes, disulfide bonds are generated by DsbB or VKOR homologs that couple the oxidation of a cysteine pair to quinone reduction. Vertebrate VKOR and VKOR-like enzymes have gained the epoxide reductase activity to support blood coagulation. The core structures of DsbB and VKOR variants share the architecture of a four-transmembrane-helix bundle that supports the coupled redox reaction and a flexible region containing another cysteine pair for electron transfer. Despite considerable similarities, recent high-resolution crystal structures of DsbB and VKOR variants reveal significant differences. DsbB activates the cysteine thiolate by a catalytic triad of polar residues, a reminiscent of classical cysteine/serine proteases. In contrast, bacterial VKOR homologs create a hydrophobic pocket to activate the cysteine thiolate. Vertebrate VKOR and VKOR-like maintain this hydrophobic pocket and further evolved two strong hydrogen bonds to stabilize the reaction intermediates and increase the quinone redox potential. These hydrogen bonds are critical to overcome the higher energy barrier required for epoxide reduction. The electron transfer process of DsbB and VKOR variants uses slow and fast pathways, but their relative contribution may be different in prokaryotic and eukaryotic cells. The quinone is a tightly bound cofactor in DsbB and bacterial VKOR homologs, whereas vertebrate VKOR variants use transient substrate binding to trigger the electron transfer in the slow pathway. Overall, the catalytic mechanisms of DsbB and VKOR variants have fundamental differences.

Structural and cellular basis of vitamin K antagonism

Vitamin K antagonists (VKAs), such as warfarin, are oral anticoagulants widely used to treat and prevent thromboembolic diseases. Therapeutic use of these drugs requires frequent monitoring and dose adjustments, whereas overdose often causes severe bleeding. Addressing these drawbacks requires mechanistic understandings at cellular and structural levels. As the target of VKAs, vitamin K epoxide reductase (VKOR) generates the active, hydroquinone form of vitamin K, which in turn drives the γ-carboxylation of several coagulation factors required for their activity. Crystal structures revealed that VKAs inhibit VKOR via mimicking its catalytic process. At the active site, two strong hydrogen bonds that facilitate the catalysis also afford the binding specificity for VKAs. Binding of VKAs induces a global change from open to closed conformation. Similar conformational change is induced by substrate binding to promote an electron transfer process that reduces the VKOR active site. In the cellular environment, reducing partner proteins or small reducing molecules may afford electrons to maintain the VKOR activity. The catalysis and VKA inhibition require VKOR in different cellular redox states, explaining the complex kinetics behavior of VKAs. Recent studies also revealed the mechanisms underlying warfarin resistance, warfarin dose variation, and antidoting by vitamin K. These mechanistic understandings may lead to improved anticoagulation strategies targeting the vitamin K cycle.