Kristin Van Mouwerik Lyles

Machupo virus (MACV) is the causal agent of Bolivian Hemorrhagic fever. It is highly pathogenic, has a high mortality rate, and currently lacks specific treatments or vaccines. MACV belongs to the Arenaviridae family, which uses a cap-snatching mechanism during the transcription process. Its viral polymerase, the L protein, harbors the endonuclease activity required for cap snatching, making it a suitable target for the development of antiviral therapeutics. We combined experimental and computational methods to characterize MACV endonuclease activity and evaluate inhibitors. A fluorescence resonance energy transfer (FRET) assay was used to measure the enzymatic activity of endonuclease and identify potent inhibitors via high-throughput screening. FRET assays identified BW-148, an inhibitor with a 48.4 µM (95% CI: 37.3–59.3 µM; R² = 0.98) IC₅₀, and a K_D of 13.7 µM (95% CI: 8.2–19.2 µM, n = 3). Docking studies reveal that BW-148 may bind near the MACV endonuclease catalytic site, inhibiting enzymatic activities by metal chelating. BW-148 is a useful lead compound for further optimization of Machupo endonuclease inhibitors.

Nucleocapsids protect viral genomes and play fundamental roles in viral assembly and infection. While many viruses adopt icosahedral or helical symmetries, negative-strand RNA viruses (NSVs) assemble their nucleocapsids with a distinct translation-based symmetry that is often considered helical because of their curvature. Our study analyzes the structural basis, assembly principles, and functional implications of the linear nucleocapsids. Structural coordinates of viruses were obtained from the Protein Data Bank (PDB) and examined using PyMOL version 1.3 to compare protein folds, RNA–protein interactions, inter-subunit contacts, and curvature properties across multiple nucleocapsids. We found that linear nucleocapsids share a similar 5H + 3H fold in their capsid proteins and encapsidate a fixed number of nucleotides per subunit, though the degree of nucleotide sequestration varies. Their architecture differs in inter-subunit interactions, determining whether empty capsids can assemble and influencing RNase sensitivity. Although these nucleocapsids may appear helical, they lack strict helical symmetry and instead display variable curvature that is modulated by environmental conditions. Relaxation of this curvature is likely required for viral RNA-dependent RNA polymerase to access the sequestered RNA genome during transcription/replication. In conclusion, linear nucleocapsids constitute a class of RNA–protein assemblies with variable curvature. The topologically conserved fold of the capsid protein enables genome protection while regulating exposure of RNA during viral RNA synthesis.

Zika virus (ZIKV) caused Zika outbreaks and continues to post threats to public health. ZIKV infection may cause congenital abnormalities during pregnancy and neurological manifestations in adults. The recurrent public health threat of Zika in various geographical areas demonstrates a need for the development of effective therapeutics. Currently, there are no approved therapies for Zika. ZIKV is a single-stranded, positive-sense RNA virus, whose genome encodes three structural proteins and seven non-structural proteins. The surface envelope (E) protein is essential for host–cell recognition and viral entry; therefore, inhibition of E-mediated viral entry is a key strategy underlying antiviral treatments. Here, molecular docking-based virtual screening was used to screen small-molecule compound libraries to identify potential ZIKV entry inhibitors. Among the compounds identified, Pyrimidine-Der1 exhibited efficient inhibition of reporter ZIKV infection. The microscale thermophoresis assay confirmed its binding with the ZIKV E protein. This compound has effective inhibition of authentic ZIKV infection in a plaque inhibition assay against R103451, PAN2016, and FLR human strains (IC₅₀: ~3–5 μM). Additionally, it efficiently inhibited ZIKV infection at viral entry and fusion steps of the virus life cycle in a time-of-addition assay. Overall, Pyrimidine-Der1 is a promising ZIKV entry inhibitor, warranting further optimization and evaluation.

Despite current vaccines and therapeutics targeting SARS-CoV-2, the causative agent of the COVID-19 pandemic, cases remain high causing a burden on health care systems. Spike-protein mediated membrane fusion of SARS-CoV-2 is a critical step in viral entry. Herein, we describe entry inhibitors identified by first screening a library of about 160 compounds and then analogue synthesis. Specifically, compound 261 was found to inhibit SARS-CoV-2 infection in a tissue model with IC₅₀ of 0.3 µM. Using NMR, we found that 261 interacts with key residues in the aromatic-rich region of the spike protein directly next to the transmembrane domain. Molecular dynamic simulations of the 261 binding pocket in the spike protein was also mapped to the transmembrane domain, consistent with NMR findings. The amino acids in the binding site are conserved among different coronaviruses known to infect humans; therefore, inhibitors targeting this conserved binding site could be a useful addition to current therapeutics and may have pan-coronavirus antiviral activities.

Arenaviruses exist globally and can cause hemorrhagic fever and neurological diseases, exemplified by the zoonotic pathogen lymphocytic choriomeningitis virus (LCMV). The structures of individual LCMV proteins or their fragments have been reported, but the architectural organization and the nucleocapsid assembly mechanism remain elusive. Importantly, the in situ structure of the arenavirus fusion protein complex (glycoprotein complex, GPC) as present on the virion prior to fusion, particularly with its integral stable signal peptide (SSP), has not been shown, hindering efforts such as structure-based vaccine design. Here, we have determined the in situ structure of LCMV proteins and their architectural organization in the virion by cryogenic electron tomography. The tomograms reveal the global distribution of GPC, matrix protein Z, and the contact points between the viral envelope and nucleocapsid. Subtomogram averaging yielded the in situ structure of the mature GPC with its transmembrane domain intact, revealing the GP2-SSP interface and the endodomain of GP2. The number of RNA-dependent RNA polymerase L molecules packaged within each virion varies, adding new perspectives to the infection mechanism. Together, these results delineate the structural organization of LCMV and offer new insights into its mechanism of LCMV maturation, egress, and cell entry. IMPORTANCE: The impact of COVID-19 on public health has highlighted the importance of understanding zoonotic pathogens. Lymphocytic choriomeningitis virus (LCMV) is a rodent-borne human pathogen that causes hemorrhagic fever. Herein, we describe the in situ structure of LCMV proteins and their architectural organization on the viral envelope and around the nucleocapsid. The virion structure reveals the distribution of the surface glycoprotein complex (GPC) and the contact points between the viral envelope and the underlying matrix protein, as well as the association with the nucleocapsid. The morphology and sizes of virions, as well as the number of RNA polymerase L inside each virion vary greatly, highlighting the fast-changing nature of LCMV. A comparison between the in situ GPC trimeric structure and prior ectodomain structures identifies the transmembrane and endo domains of GPC and key interactions among its subunits. The work provides new insights into LCMV assembly and informs future structure-guided vaccine design.

It has been shown that the response rate of TNBC is dependent on the level of PD-L1 and the tumor microenvironment (TME). Approaches that alter the TME can improve the efficacy of ICIs. Background: We have engineered a Smac-armed oncolytic virus by inserting a Smac transgene into the genome of a vesicular stomatitis virus to generate VSV-S. Our previous study shows that the anticancer efficacy of VSV-S is more potent than that of wild-typed VSV in a subcutaneous TNBC mouse model. VSV-S treatment reverts the immunosuppressive TME by reducing MDSCs and TAMs, while increasing infiltration of neutrophils and CD8+ T cells. Methods: VSV-S was used to treat TNBC in an orthotopic mouse model, and in a combination therapy with an anti-PD-1 antibody to treat metastatic TNBC in a mouse model. Changes in the TME were evaluated. Results: In this current study, we show that neoadjuvant VSV-S treatment of primary orthotopic TNBC tumors in mice drastically lowered lung metastasis after surgical removal of the primary tumor, and significantly increased the survival rate. The mechanism of action and changes to the TME were delineated, among which one significant marker is the elevation of PD-L1 expression in tumors. In the TNBC lung metastasis mouse model, pulmonary treatment with VSV-S greatly enhanced the efficacy of ICI treatment. Conclusions: Our results suggest that the combination of oncolytic virus and ICI therapies has the potential to substantially improve the outcome of TNBC treatment.

The rapid and persistent emergence of drug-resistant bacteria poses a looming public health crisis. The possible task of developing new sets of antibiotics to replenish the existing ones is daunting to say the least. Searching for adjuvants that restore or even enhance the potency of existing antibiotics against drug-resistant strains of bacteria represents a practical and cost-effective approach. Herein, we describe the discovery of potent adjuvants that extend the antimicrobial spectrum of existing antibiotics and restore their effectiveness toward drug-resistant strains including mcr-1-expressing strains. From a library of cationic compounds, MD-100, which has a diamidine core structure, was identified as a potent antibiotic adjuvant against Gram-negative bacteria. Further optimization efforts including the synthesis of ∼20 compounds through medicinal chemistry work led to the discovery of a much more potent compound MD-124. MD-124 was shown to sensitize various Gram-negative bacterial species and strains, including multidrug resistant pathogens, toward existing antibiotics with diverse mechanisms of action. We further demonstrated the efficacy of MD-124 in an ex vivo skin infection model and in an in vivo murine systemic infection model using both wild-type and drug-resistant Escherichia coli strains. MD-124 functions through selective permeabilization of the outer membrane of Gram-negative bacteria. Importantly, bacteria exhibited low-resistance frequency toward MD-124. In-depth computational investigations of MD-124 binding to the bacterial outer membrane using equilibrium and steered molecular dynamics simulations revealed key structural features for favorable interactions. The very potent nature of such adjuvants distinguishes them as very useful leads for future drug development in combating bacterial drug resistance.

Group A Streptococcus (GAS) is a major pathogen that causes simple and invasive infections. GAS requires iron for metabolic processes and pathogenesis, and heme is its preferred iron source. We previously described the iron-regulated hupZ in GAS, showing that a recombinant HupZ-His₆ protein binds and degrades heme. The His₆ tag was later implicated in heme iron coordination by HupZ-His₆. Hence, we tested several recombinant HupZ proteins, including a tag-free protein, for heme binding and degradation in vitro. We established that HupZ binds heme but without coordinating the heme iron. Heme-HupZ readily accepted exogenous imidazole as its axial heme ligand, prompting degradation. Furthermore, HupZ bound a fragment of heme c (whose iron is coordinated by the cytochrome histidine residue) and exhibited limited degradation. GAS, however, did not grow on a heme c fragment as an iron source. Heterologous HupZ expression in Lactococcus lactis increased heme b iron use. A GAS hupZ mutant showed reduced growth when using hemoglobin as an iron source, increased sensitivity to heme toxicity, and decreased fitness in a murine model for vaginal colonization. Together, the data demonstrate that HupZ contributes to heme metabolism and host survival, likely as a heme chaperone. HupZ is structurally similar to the recently described heme c-degrading enzyme, Pden_1323, suggesting that the GAS HupZ might be divergent to play a new role in heme metabolism.

A vaccine against group A Streptococcus (GAS) has been actively pursued for decades. The surface receptor Shr is vital in GAS heme uptake and provides an effective target for active and passive immunization. Here, we isolated human monoclonal antibodies (mAbs) against Shr and evaluated their efficacy and mechanism. We used a single B-lymphocyte screen to discover the mAbs TRL186 and TRL96. Interactions of the mAbs with whole cells, proteins, and peptides were investigated. Growth assays and cultured phagocytes were used to study the mAbs’ impact on heme uptake and bacterial killing. Efficacy was tested in prophylactic and therapeutic vaccination using intraperitoneal mAb administration and GAS challenge Both TRL186 and TRL96 interact with whole GAS cells, recognizing the NTR and NEAT1 domains of Shr, respectively. Both mAbs promoted killing by phagocytes in vitro, but prophylactic administration of only TRL186 increased mice survival. TRL186 improved survival also in a therapeutic mode. TRL186 but not TRL96 also impeded Shr binding to hemoglobin and GAS growth on hemoglobin iron. Interference with iron acquisition is central for TRL186 efficacy against GAS. This study supports the concept of antibody-based immunotherapy targeting the heme uptake proteins to combat streptococcal infections.

Group A Streptococcus (GAS) produces millions of infections worldwide, including mild mucosal infections, post-infection sequelae, and life-threatening invasive diseases. During infection, GAS readily acquires nutritional iron from the host heme and hemoproteins. Here, we identified a new heme importer, named SiaFGH, and investigated its role in GAS pathophysiology. The SiaFGH proteins belong to a group of transporters with an unknown ligand from the recently described family of Energy Coupling Factor (ECF). A siaFGH deletion mutant exhibited higher streptonigrin resistance comparing to the parental strain, suggesting that iron ion or an iron-complex is the likely ligand. Iron uptake and ICP-MS studies showed that the loss of siaFGH did not impact GAS import of ferric or ferrous iron, but the mutant was impaired in using hemoglobin iron for growth. Analysis of cells growing on hemoglobin iron revealed a substantial decrease in cellular heme content in the mutant comparing to the complemented strain. Induction of the siaFGH genes in trans resulted in the induction of heme uptake. The siaFGH mutant exhibited a significant impairment in murine models for mucosal colonization and systemic infection. Together the data show that SiaFGH is a new type of heme importer that is key for GAS use of host hemoproteins and that this system is imperative for bacterial colonization and invasive infection. Importance ECF systems are new transporters that take up various vitamins, cobalt, or nickel in high affinity. Here we expand this paradigm and establish the GAS SiaFGH proteins as a new ECF module that imports heme and demonstrates its importance in virulence. SiaFGH is the first heme ECF system described in bacteria. We identified homologous systems in the genomes of related pathogens from the Firmicutes phylum. Notably, GAS and other pathogens that use a SiaFGH-type importer, are relying on host hemoproteins for a source of iron during infection. Hence, recognizing the function of this noncanonical ABC transporter in heme acquisition and the critical role it plays in disease has broad implications.