Abstract Title
Pandemic GII.4/Sydney VLP exhibits decreased conformational flexibility compared to a GII.4 consensus VLP vaccine candidate
Presenter
Ramakrishnan Anish, Baylor College of Medicine
Co-Author(s)
Ramakrishnan Anish1, Carmen V. Apostol1, Janam Dave2, Michael E. Abram4, Son Pham1, Frederick H. Neill2, Robert L. Atmar2,3, Mary K. Estes2,3 and 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, 4 Hillevax, Inc., Boston, MA, USA
Abstract Category
Structure & Pathogenesis
Abstract
Epochally evolving GII.4 strains of human noroviruses (HuNoVs) cause most cases of acute gastroenteritis globally. The major structural protein VP1, with a shell (S) and protruding (P) domain linked by a flexible hinge, alone or with the minor structural protein VP2, assembles into virus-like particles (VLPs) with native-like T=3 and non-native T=4 icosahedral structures. The capsid is susceptible to environmental factors like pH and divalent cations, with VP1 undergoing reversible transitions between resting and raised conformations facilitated by the hinge. While VLP-based and mRNA vaccines are attractive options, their efficacy is hampered by incomplete understanding of how capsid plasticity affects immunogenicity.
Here, we report cryo-EM and biophysical studies comparing the pandemic GII.4/Sydney/2012 (VP1+VP2) and GII.4/consensus/2002-2006 (GII.4c, VP1) VLPs. GII.4/Sydney/2012 exhibits 1:1 distribution of resting T=3 and raised T=4 particles. At 2.8 Å, the T=3 organization is comparable to the previous GII.4/HOV/2002 structure, despite the absence of a stabilizing metal cation at the P-dimer interface. By comparison, GII.4c also exhibits 1:1 distribution of T=3 and T=4 particles, but strikingly both are in the raised conformations, with high flexibility in the P domains. Dynamic light scattering, bis-ANS binding, and differential scanning fluorimetry showed that GII.4/Sydney/2012 is less sensitive to changes in pH and metal ions, which trigger conformational changes in GII.4/HOV/2002 and GII.4c VLPs. Despite different kinetics of capsid dynamics, both GII.4/Sydney and GII.4c were destabilized by M4 nanobody, which binds to the raised conformation of VP1. Understanding the determinants of HuNoV capsid dynamics is crucial for designing more efficacious vaccines.
Here, we report cryo-EM and biophysical studies comparing the pandemic GII.4/Sydney/2012 (VP1+VP2) and GII.4/consensus/2002-2006 (GII.4c, VP1) VLPs. GII.4/Sydney/2012 exhibits 1:1 distribution of resting T=3 and raised T=4 particles. At 2.8 Å, the T=3 organization is comparable to the previous GII.4/HOV/2002 structure, despite the absence of a stabilizing metal cation at the P-dimer interface. By comparison, GII.4c also exhibits 1:1 distribution of T=3 and T=4 particles, but strikingly both are in the raised conformations, with high flexibility in the P domains. Dynamic light scattering, bis-ANS binding, and differential scanning fluorimetry showed that GII.4/Sydney/2012 is less sensitive to changes in pH and metal ions, which trigger conformational changes in GII.4/HOV/2002 and GII.4c VLPs. Despite different kinetics of capsid dynamics, both GII.4/Sydney and GII.4c were destabilized by M4 nanobody, which binds to the raised conformation of VP1. Understanding the determinants of HuNoV capsid dynamics is crucial for designing more efficacious vaccines.