Adonis, J. | Search bioRxiv

bioRxiv2026

Small molecule inhibition of the mitochondrial lipid transfer protein STARD7 attenuates influenza viral replication

The increasing appearance of drug-resistant and zoonotic influenza strains highlights an urgent need for host-directed antivirals that offer broad-spectrum activity and a higher barrier to resistance. Here, we describe the characterization of M4, a small-molecule identified from a high-thoughput screen that potently inhibits influenza A and B viruses. Mechanistic studies reveal that M4 suppresses replication by causing nuclear retention of the viral ribonucleoprotein (vRNP) complex. Chemoproteomic profiling identified the lipid transfer protein STARD7 as the primary cellular target, and genetic depletion of STARD7 phenocopies the antiviral effects of M4. Additional studies localizes the M4 binding site to cysteine 302 within the lipid-binding domain of STARD7, supporting a model in which STARD7-dependent lipid transfer activity promotes efficient vRNP trafficking and nuclear export. Combining M4 with baloxavir enhances antiviral efficacy in a murine infection model, providing in vivo support for a host-directed strategy. Together, these results identify STARD7 as a metabolic checkpoint licensing vRNP export and establish a proof of concept for therapeutic intervention with small molecule inhibitors. Author SummaryInfluenza viruses continue to cause widespread illness and pose an ongoing pandemic threat, in part because existing antiviral drugs can lose effectiveness as the virus evolves resistance. To address this challenge, we focused on identifying therapies that target host cell processes required for viral replication, rather than viral proteins themselves. In this study, we describe a small molecule, M4, that inhibits replication of both influenza A and B viruses by blocking a critical step in the viral life cycle. We found that M4 acts on a host protein called STARD7, which helps move certain lipids to the right places inside cells. When STARD7 is inhibited, the influenza viral ribonucleoprotein (vRNP) complex becomes trapped in the cell nucleus and cannot reach the cytoplasm, preventing the virus from completing its replication cycle. Disrupting STARD7 genetically produces the same effect, confirming that this host protein is important for influenza replication. These findings point to a previously unrecognized host gating mechanism that controls nuclear export of the vRNP complex during infection. Although M4 alone showed limited activity in animals, combining it with an existing antiviral drug strongly improved antiviral efficacy. Together, our results reveal a new host pathway that influenza viruses rely on and support host-directed combination approaches to strengthen antiviral treatment and help counter drug resistance.

microbiology↗

bioRxiv2026

Identification of novel inhibitors of Mycobacterium smegmatis growth through genome-wide overexpression of Cluster P3 mycobacteriophage Xavia genes

We examined whether genes encoded by the mycobacteriophage Xavia disrupt growth of Mycobacterium smegmatis, a widely used mycobacterial model. Seventy-one Xavia genes were individually expressed using an inducible plasmid system and assessed for effects on colony formation. Two genes were lethal even without induction, indicating toxicity under basal expression. Induction of sixteen additional genes reduced bacterial growth, spanning structural proteins, lysogeny regulators, DNA-associated enzymes, a lysis protein, and several genes with no known function. These findings expand functional insights into mycobacteriophage gene repertoires and identify candidates for future mechanistic studies. AbstractBacteriophage genomes encode large numbers of genes with no known function, and many of these genes affect essential host processes when expressed in a heterologous system. For mycobacteriophages, genome-wide overexpression in Mycobacterium smegmatis provides a direct way to identify proteins that impair growth and to determine which mycobacterial pathways are sensitive to phage gene products. To evaluate the cytotoxic potential of the Cluster P3 phage Xavia, a lineage that has not undergone functional screening, we constructed an arrayed pExTra library containing 71 predicted Xavia genes under control of the anhydrotetracycline inducible promoter pTet. All constructs were sequence-verified and transformed into M. smegmatis, and induction allowed measurement of gene-specific effects on growth. Two genes prevented recovery of transformants, suggesting toxicity under basal promoter leakiness. Inducible expression of 16 additional genes impaired growth, and these inhibitory proteins include structural components, regulators of lysogeny, enzymes of DNA metabolism, a lysis factor, and several proteins with no known function. Four of the strongest inhibitors were genes with no known function. These results extend functional screening into the previously untested P3 branch of Actinobacteriophages and identify new proteins that require mechanistic analysis.

microbiology↗