Functional Diversity in GII.4 Norovirus Entry: HBGA Binding and Capsid Clustering Dynamics

Area of Science:

• Virology
• Cell Biology
• Gastroenterology

Background:

• Human noroviruses (HuNoVs), particularly GII.4 strains, are a major cause of viral gastroenteritis globally.
• Current therapeutic options, including vaccines and antivirals, are limited for HuNoVs.
• The cell entry mechanism of GII.4 Sydney involves membrane wounding and CLIC-mediated endocytosis, but its conservation across variants is unknown.

Purpose of the Study:

• To investigate the conserved cell entry mechanisms of human norovirus GII.4 variants.
• To compare the early binding and entry processes of different GII.4 strains.
• To identify key viral factors and host cell processes involved in GII.4 norovirus cell entry.

Main Methods:

• Utilized wildtype and mutant GII.4 virus-like particles (VLPs) for comparative analysis.
• Employed modified human intestinal enteroid (HIE) cultures to model intestinal cell infection.
• Performed inhibitor studies targeting host cell pathways and analyzed VLP mutations.

Main Results:

• Only a subset of GII.4 variants formed distinct, HBGA-dependent capsid clusters on cell surfaces.
• Clustering variants demonstrated significantly enhanced membrane wounding and endocytosis compared to non-clustering variants.
• Specific VP1 residues (V333 and R339) were identified as critical for clustering and entry, independent of HBGA binding.
• Clustering and endocytosis were driven by lipid raft remodeling, regulated by cholesterol and ceramides, not host protein glycosylation.
• A dichotomy between clustering (high entry competence) and non-clustering phenotypes was observed across GII.4 variants.

Conclusions:

• Cell entry mechanisms vary among GII.4 norovirus variants, with clustering being a key determinant of entry competence.
• Specific VP1 residues mediate clustering and subsequent membrane-associated entry processes.
• Understanding these strain-specific mechanisms provides insights into norovirus pathogenesis and potential therapeutic targets.