Dengue is the most prevalent arthropod-borne viral disease worldwide and affects approximately 2.5 billion people living in over 100 countries. Increasing geographic expansion of Aedes aegypti mosquitoes (which transmit the virus) has made dengue a global health concern. There are currently no approved antivirals available to treat dengue, and the only approved vaccine used in some countries is limited to seropositive patients. Treatment of dengue, therefore, remains largely supportive to date; hence, research efforts are being intensified for the development of antivirals. The nonstructural proteins, 3 and 5 (NS3 and NS5), have been the major targets for dengue antiviral development due to their indispensable enzymatic and biological functions in the viral replication process. NS5 is the largest and most conserved nonstructural protein encoded by flaviviruses. Its multifunctionality makes it an attractive target for antiviral development, but research efforts have, this far, not resulted in the successful development of an antiviral targeting NS5. Increase in structural insights into the dengue NS5 protein will accelerate drug discovery efforts focused on NS5 as an antiviral target. In this review, we will give an overview of the current state of therapeutic development, with a focus on NS5 as a therapeutic target against dengue.

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ABSTRACTBromodomain-containing proteins are often part of chromatin-modifying complexes, and their activity can lead to altered expression of genes that drive cancer, inflammation and neurological disorders in humans. Bromodomain-PHD finger protein 1 (BRPF1) is part of the MOZ (monocytic leukemic zinc-finger protein) HAT (histone acetyltransferase) complex, which is associated with chromosomal translocations known to contribute to the development of acute myeloid leukemia (AML). BRPF1 contains a unique combination of chromatin reader domains including two plant homeodomain (PHD) fingers separated by a zinc knuckle (PZP domain), a bromodomain, and a proline-tryptophan-tryptophan-proline (PWWP) domain. BRPF1 is known to recruit the MOZ HAT complex to chromatin by recognizing acetylated lysine residues on the N-terminal histone tail region through its bromodomain. However, histone proteins can contain several acetylation modifications on their N-terminus, and it is unknown how additional marks influence bromodomain recruitment to chromatin. Here, we identify the BRPF1 bromodomain as a selective reader of di-acetyllysine modifications on histone H4. We used ITC assays to characterize the binding of di-acetylated histone ligands to the BRPF1 bromodomain and found that the domain binds preferentially to histone peptides H4K5acK8ac and H4K5acK12ac. Analytical ultracentrifugation (AUC) experiments revealed that the monomeric state of the BRPF1 bromodomain coordinates di-acetylated histone ligands. NMR chemical shift perturbation studies, along with binding and mutational analyses, revealed non-canonical regions of the bromodomain-binding pocket that are important for histone tail recognition. Together, our findings provide critical information on how the combinatorial action of post-translational modifications can modulate BRPF1 bromodomain binding and specificity.

Background Deficiency in blood coagulation factor VIII (FVIII) results in life‐threating bleeding (hemophilia A) treated by infusions of FVIII concentrates. To improve disease treatment, FVIII has been modified to increase its plasma half‐life, which requires understanding mechanisms of FVIII catabolism. An important catabolic actor is hepatic low density lipoprotein receptor‐related protein 1 (LRP1), which also regulates many other clinically significant processes. Previous studies showed complexity of FVIII site for binding LRP1. Objectives To characterize binding sites between FVIII and LRP1 and suggest a model of the interaction. Methods A series of recombinant ligand‐binding complement‐type repeat (CR) fragments of LRP1 including mutated variants was generated in a baculovirus system and tested for FVIII interaction using surface plasmon resonance, tissue culture model, hydrogen–deuterium exchange mass spectrometry, and in silico. Results Multiple CR doublets within LRP1 clusters II and IV were identified as alternative FVIII‐binding sites. These interactions follow the canonical binding mode providing major binding energy, and additional weak interactions are contributed by adjacent CR domains. A representative CR doublet was shown to have multiple contact sites on FVIII. Conclusions FVIII and LRP1 interact via formation of multiple complex contacts involving both canonical and non‐canonical binding combinations. We propose that FVIII‐LRP1 interaction occurs via switching such alternative binding combinations in a dynamic mode, and that this mechanism is relevant to other ligand interactions of the low‐density lipoprotein receptor family members including LRP1.

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Iron is an essential element for nearly all organisms, and under anoxic and/or reducing conditions, Fe2+ is the dominant form of iron available to bacteria. The ferrous iron transport (Feo) system has been identified as the primary prokaryotic Fe2+ import machinery, and two proteins (FeoA and FeoB) are conserved across most bacterial species. However, how FeoA and FeoB function relative to one another remained enigmatic. In this work we explored the distribution of feoAB operons predicted to encode for a fusion of FeoA tethered to the soluble N-terminal, G-protein domain of FeoB via a connecting linker region. We hypothesized that this fusion might poise FeoA to interact with FeoB in order to affect function. To test this hypothesis, we cloned, expressed, purified, and biochemically characterized the soluble NFeoAB fusion protein from Bacteroides fragilis, a commensal organism implicated in drug-resistant peritoneal infections. Using X-ray crystallography, we determined to 1.50 Å resolution the structure of BfFeoA, which adopts an SH3-like fold implicated in protein-protein interactions. In combination with structural modeling, small-angle X-ray scattering, and hydrogen-deuterium exchange mass spectrometry, we show that FeoA and NFeoB indeed interact in a nucleotide-dependent manner, and we have mapped the protein-protein interaction interface. Finally, using GTP hydrolysis assays, we demonstrate that BfNFeoAB exhibits one of the slowest known rates of Feo-mediated GTP hydrolysis and is not potassium-stimulated, indicating that FeoA-NFeoB interactions may function to stabilize the GTP-bound form of FeoB. Our work thus reveals a role for FeoA function in the fused FeoAB systems and suggests a broader role for FeoA function amongst prokaryotes.

Dengue is the most prevalent arthropod-borne disease globally and affects approximately 2.5 billion people living in over 100 countries. The increasing geographic expansion of Aedes aegypti mosquitoes which transmit the virus has made dengue fever a global health concern. There are currently no approved antivirals available to treat dengue, and the only approved vaccine used in some countries is limited to seropositive patients. Treatment of dengue therefore remains largely supportive to date; hence research efforts are being intensified for the development of antivirals against dengue. The NS3 and NS5 nonstructural proteins have been the major targets for dengue antiviral development due to their indispensable enzymatic and biological functions in the viral replication process. NS5 is the largest and most conserved nonstructural protein encoded by flaviviruses including dengue. Its multifunctionality makes it an attractive target for antiviral development against dengue, but research efforts are hindered due to its limited structural characterization compared to the NS5 of other flaviviruses like the Zika virus. Increase in structural insights into the dengue NS5 protein will accelerate drug discovery efforts focused on NS5 as an antiviral target. In this review, we will give an overview of the current state of therapeutic development against dengue.