Defect-Engineered Core–Shell MOF Nanointerface Functionalized with Hemagglutinin for Target-Guided Anti-influenza Ligand Discovery

Abstract Preserving the biological function of conformationally dynamic proteins after immobilization remains a major challenge in biointerface engineering. Here, a defect-engineered hierarchical MOF nanointerface (D-MOF-808-HET@MOF-808@SiO2) was constructed through evaporation-induced interfacial coordination assembly for hemagglutinin (HA) immobilization and target-guided ligand screening. XPS analysis supported coordination-mediated interactions between HA and accessible Zr sites of the defect-engineered interface, as indicated by altered Zr 3d and O 1s binding energies. The immobilized HA retained a hemagglutination titer above 5.0 log2, indicating preservation of its biological activity. The HA-functionalized interface interfered with viral attachment to host cells during the early stage of H1N1 PR8 infection and was subsequently used as an affinity matrix to enrich HA-associated constituents from Mahuang-Xixin-Fuzi Decoction. Twelve candidate ligands were identified, of which hypaconitine, naringenin, ethyl caffeate, and vitexin were further evaluated by surface plasmon resonance and cellular antiviral assays. Hypaconitine exhibited the strongest HA-binding affinity (KD = 1.72 μM) but showed relatively weak antiviral activity (EC50 = 50.03 μM), whereas ethyl caffeate and vitexin displayed superior antiviral activities (EC50 = 1.54 and 2.56 μM) despite moderate HA affinities (KD = 11.06 and 12.20 μM, respectively), revealing an affinity–activity mismatch. Molecular docking predicted different ligand interaction patterns, with ethyl caffeate and vitexin showing interactions near the HA1–HA2 interdomain region, whereas hypaconitine and naringenin exhibited alternative predicted interaction regions. These differences in predicted binding modes may contribute to the observed functional disparity. These findings suggest that equilibrium affinity alone does not fully account for antiviral activity and support HA-functionalized MOF nanointerfaces as a platform for target-guided screening of bioactive constituents from complex natural-product mixtures.