Novel Structural Features of Human Norovirus Capsid

Abstract

16Human noroviruses are a major cause of gastroenteritis, yet there are still no vaccines 17 or antivirals available. Nevertheless, a number of vaccine candidates that are currently 18 in clinical trials are composed of norovirus virus-like particles (VLPs). These VLPs 19 are recognized as morphologically and antigenically similar to norovirus virions. An 20 X-ray crystal structure of the prototype (GI.1) VLPs showed that the norovirus capsid 21 has a T=3 icosahedral symmetry and is composed of 180 copies of the major capsid 22 protein (VP1) that folds into three quasi-equivalent subunits (A, B, and C). In this 23 study, we determined the cryo-EM structure of VLPs for two GII.4 noroviruses that 24were detected in 1974 and 2012. We showed that these VLPs had a T=4 symmetry 25 and were composed of 240 copies of VP1. The VP1 on the T=4 VLPs adapted four 26 quasi-equivalent subunits (termed A, B, C, and D), which formed two distinct dimers 27 (A/B and C/D). We found that the T=4 protruding domain was elevated ~21 Å off the 28 capsid shell, which was ~7 Å more than the previously determined for the T=3 GII.10 29 norovirus. Another interesting feature of the T=4 VLPs was a small cavity and flap-30 like structure located at the twofold axis. This structural feature was associated with 31 the shell domain (D subunit) and disrupted the contiguous shell. Altogether, we 32 showed that the T=4 VLPs had a number of structural similarities and differences 33 with other noroviruses, but how these structural changes associate with norovirus 34 virions could be important for vaccine studies. 35 65 tolerated, highly immunogenic, and appeared to be safe, since they did not comprise 66 of live or attenuated virus. However, limitations of the current vaccine formulations 67 included mild norovirus like-symptoms, restricted long-term immunity, and limited 68 cross-protection (5, 6). 69 70 Structural analysis of GI.1 VLPs reveals that VP1 is separated into two distinct 71 domains: a shell domain (S domain) that encloses the RNA and a protruding domain 72 Journal of physics. Condensed matter : an Institute of Physics journal 421 30:064006.

Development of a Specific Anti-capsid Antibody- and Magnetic Bead-Based Immunoassay to Detect Human Norovirus Particles in Stool Samples and Spiked Mussels via Flow Cytometry

“…However, since the S domain is localised at the capsid interior, parts of it can be less accessible to antibodies. The P domain has recently been shown to support two conformations (Smith & Smith, 2019), namely the rising conformation as evidenced in MNV (Katpally et al, 2008), HuNoV GII.10 (Hansman et al, 2012 and GII.4 (Devant et al, 2019), where the P domain rises from the S domain surface, and the resting conformation as represented by GI.1 (Prasad et al, 1999) and GII.2 viruses (Jung et al, 2019), where the P domain rests upon the S domain. Moreover, dynamic conformational changes have been reported for MNV and HuNoV GII.3; whilst the MNV conformational changes have been reported in response to aqueous conditions (the P domain rises from the S domain surface in solutions with higher pH and rests in solutions with lower pH (Song et al, 2020)), the mechanism is yet unclear for GII.3 viruses.…”