Small Molecule Assembly\nAgonist Alters the Dynamics\nof Hepatitis B Virus Core Protein Dimer and Capsid

Chronic hepatitis B virus (HBV) poses a significant public\nhealth\nburden worldwide, encouraging the search for curative antivirals.\nOne approach is capsid assembly modulators (CAMs), which are assembly\nagonists. CAMs lead to empty and defective capsids, inhibiting the\nformation of new viruses, and can also lead to defects in the release\nof the viral genome, inhibiting new infections. In this study, we\nemployed hydrogen–deuterium exchange mass spectrometry (HDX-MS)\nto assess the impact of one such CAM, HAP18, on HBV dimers, capsids\ncomposed of 120 (or 90) capsid protein dimers, and cross-linked capsids\n(xl-capsids). HDX analysis revealed hydrogen bonding networks within\nand between the dimers. HAP18 disrupted the hydrogen bonding network\nof dimers, demonstrating a previously unappreciated impact on the\ndimer structure. Conversely, HAP18 stabilized both unmodified and\ncross-linked capsids. Intriguingly, cross-linking the capsid, which\nwas accomplished by forming disulfides between an engineered C-terminal\ncysteine, increased the overall rate of HDX. Moreover, HAP18 binding\ninduced conformational changes beyond the binding sites. Our findings\nprovide evidence for allosteric communication within and between capsid\nprotein dimers. These results show that CAMs are capable of harnessing\nthis allosteric network to modulate the dimer and capsid dynamics.