Abstract Title
pH and Bile Acid Differentially Regulate Human Norovirus GII.3 Capsid Dynamics
Presenter
Carmen Apostol, Baylor College of Medicine
Co-Author(s)
Carmen Apostol1, Ramakrishnan Anish1, Son Pham1, Frederick H. Neill2, Khalil Ettayebi2, B. Vijayalakshmi Ayyar2, Robert L. Atmar2,3, Mary K. Estes2,3, B. V. Venkataram Prasad1,2
1Verna and Marrs McLean Department of Biochemistry and Molecular Pharmacology, Baylor College of Medicine, Houston, TX, USA, 2Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX, USA, 3Department of Medicine, Baylor College of Medicine, Houston, TX, USA
Abstract Category
Structure & Pathogenesis
Abstract
Human noroviruses (HuNoVs), the leading cause of acute gastroenteritis globally, lack licensed therapeutics or vaccines. The GII.4 strains cause most illnesses, whereas GII.3 and others cause sporadic infections. Virus-like particles (VLPs), composed of the major (VP1) and minor structural (VP2) proteins, are promising vaccine candidates. However, antigenic variations, conformational flexibility, and assembly heterogeneity pose significant obstacles to their efficacy. VP1, with a shell (S) and a protruding (P) domain connected by a flexible linker, assembles into native-like icosahedral T=3 and non-native T=1 and T=4 VLPs. HuNoV and other NoV capsids are susceptible to environmental factors like pH, divalent cations, and bile acid (BA), with VP1 undergoing reversible transitions between resting and raised conformations. GII.3 requires BA for endocytosis and replication in culture, but the underlying mechanism remains unclear.
Here, we report that BA and pH differentially affect GII.3 capsid dynamics using biophysical and cryo-EM methods. Dynamic light scattering (DLS) and Bis-ANS binding experiments show a reduced GII.3 VLP diameter in basic versus acidic pH, corresponding to resting and raised conformations, respectively, as revealed by cryoEM. BA promotes a resting conformation even at low pH, likely through direct BA-VLP interactions. Differential scanning fluorimetry (DSF) indicates increased thermal stability at low pH, unaffected by BA. Cryo-EM confirmed extensive structural flexibility at low pH without BA, including raised T=1 and T=4 capsids and resting T=3 structures with lowered resolution around P domains. This work sheds light on capsid stability and plasticity determinants, critical factors in understanding HuNoV entry and vaccine design.
Here, we report that BA and pH differentially affect GII.3 capsid dynamics using biophysical and cryo-EM methods. Dynamic light scattering (DLS) and Bis-ANS binding experiments show a reduced GII.3 VLP diameter in basic versus acidic pH, corresponding to resting and raised conformations, respectively, as revealed by cryoEM. BA promotes a resting conformation even at low pH, likely through direct BA-VLP interactions. Differential scanning fluorimetry (DSF) indicates increased thermal stability at low pH, unaffected by BA. Cryo-EM confirmed extensive structural flexibility at low pH without BA, including raised T=1 and T=4 capsids and resting T=3 structures with lowered resolution around P domains. This work sheds light on capsid stability and plasticity determinants, critical factors in understanding HuNoV entry and vaccine design.