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+.

Structural basis of ferroportin inhibition by minihepcidin PR73.

Ferroportin (Fpn) is the only known iron exporter in humans and is essential for maintaining iron homeostasis. Fpn activity is suppressed by hepcidin, an endogenous peptide hormone, which inhibits iron export and promotes endocytosis of Fpn. Hepcidin deficiency leads to hemochromatosis and iron-loading anemia. Previous studies have shown that small peptides that mimic the first few residues of hepcidin, i.e., minihepcidins, are more potent than hepcidin. However, the mechanism of enhanced inhibition by minihepcidins remains unclear. Here, we report the structure of human ferroportin in complex with a minihepcidin, PR73 that mimics the first 9 residues of hepcidin, at 2.7 Å overall resolution. The structure reveals novel interactions that were not present between Fpn and hepcidin. We validate PR73-Fpn interactions through binding and transport assays. These results provide insights into how minihepcidins increase inhibition potency and will guide future development of Fpn inhibitors.

Unbiased discovery of autoantibodies associated with severe COVID-19 via genome-scale self-assembled DNA-barcoded protein libraries.

Pathogenic autoreactive antibodies that may be associated with life-threatening coronavirus disease 2019 (COVID-19) remain to be identified. Here, we show that self-assembled genome-scale libraries of full-length proteins covalently coupled to unique DNA barcodes for analysis by sequencing can be used for the unbiased identification of autoreactive antibodies in plasma samples. By screening 11,076 DNA-barcoded proteins expressed from a sequence-verified human ORFeome library, the method, which we named MIPSA (for Molecular Indexing of Proteins by Self-Assembly), allowed us to detect circulating neutralizing type-I and type-III interferon (IFN) autoantibodies in five plasma samples from 55 patients with life-threatening COVID-19. In addition to identifying neutralizing type-I IFN-α and IFN-ω autoantibodies and other previously known autoreactive antibodies in patient plasma, MIPSA enabled the detection of as yet unidentified neutralizing type-III anti-IFN-λ3 autoantibodies that were not seen in healthy plasma samples or in convalescent plasma from ten non-hospitalized individuals with COVID-19. The low cost and simple workflow of MIPSA will facilitate unbiased high-throughput analyses of protein-antibody, protein-protein and protein-small-molecule interactions.

Neutralizing IFNL3 Autoantibodies in Severe COVID-19 Identified Using Molecular Indexing of Proteins by Self-Assembly.

Unbiased antibody profiling can identify the targets of an immune reaction. A number of likely pathogenic autoreactive antibodies have been associated with life-threatening SARS-CoV-2 infection; yet, many additional autoantibodies likely remain unknown. Here we present Molecular Indexing of Proteins by Self Assembly (MIPSA), a technique that produces ORFeome-scale libraries of proteins covalently coupled to uniquely identifying DNA barcodes for analysis by sequencing. We used MIPSA to profile circulating autoantibodies from 55 patients with severe COVID-19 against 11,076 DNA-barcoded proteins of the human ORFeome library. MIPSA identified previously known autoreactivities, and also detected undescribed neutralizing interferon lambda 3 (IFN-λ3) autoantibodies. At-risk individuals with anti- IFN-λ3 antibodies may benefit from interferon supplementation therapies, such as those currently undergoing clinical evaluation.

Converting Light Energy to Chemical Energy: A New Catalytic Approach for Sustainable Environmental Remediation.

We report a synthetic approach to form cubic Cu2O/Pd composite structures and demonstrate their use as photocatalytic materials for tandem catalysis. Pd nanoparticles were deposited onto Cu2O cubes, and their tandem catalytic reactivity was studied via the reductive dehalogenation of polychlorinated biphenyls. The Pd content of the materials was gradually increased to examine its influence on particle morphology and catalytic performance. Materials were prepared at different Pd amounts and demonstrated a range of tandem catalytic reactivity. H2 was generated via photocatalytic proton reduction initiated by Cu2O, followed by Pd-catalyzed dehalogenation using in situ generated H2. The results indicate that material morphology and composition and substrate steric effects play important roles in controlling the overall reaction rate. Additionally, analysis of the postreacted materials revealed that a small number of the cubes had become hollow during the photodechlorination reaction. Such findings offer important insights regarding photocatalytic active sites and mechanisms, providing a pathway toward converting light-based energy to chemical energy for sustainable catalytic reactions not typically driven via light.