Production of infectious reporter murine norovirus by VP2 trans-complementation.

Human norovirus (HuNoV) causes gastroenteritis, a disease with no effective therapy or vaccine, and does not grow well in culture. Murine norovirus (MNV) easily replicates in cell cultures and small animals and has often been used as a model to elucidate the structural and functional characteristics of HuNoV. An MNV plasmid-based reverse genetics system was developed to produce the modified recombinant virus. In this study, we attempted to construct the recombinant virus by integrating a foreign gene into MNV ORF3, which encodes the minor structural protein VP2. Deletion of VP2 expression abolished infectious particles from MNV cDNA clones, and supplying exogenous VP2 to the cells rescued the infectivity of cDNA clones without VP2 expression. In addition, the coding sequence of C-terminal ORF3 was essential for cDNA clones compensated with VP2 to produce infectious particles. Furthermore, the recombinant virus with exogenous reporter genes in place of the dispensable region of ORF3 was propagated when VP2 was constitutively supplied. Our findings indicate that foreign genes can be transduced into the norovirus ORF3 region when VP2 is supplied and that successive propagation of modified recombinant norovirus could lead to the development of norovirus-based vaccines or therapeutics.IMPORTANCEIn this study, we revealed that some of the coding regions of ORF3 could be replaced by a foreign gene and infectious virus could be produced when VP2 was supplied. Propagation of this virus depended on VP2 being supplied in trans, indicating that this virus could infect only once. Our findings help to elucidate the functions of VP2 in the virus lifecycle and to develop other caliciviral vectors for recombinant attenuated live enteric virus vaccines or therapeutics tools.

Practical N-to-C peptide synthesis with minimal protecting groups.

Accessible drug modalities have continued to increase in number in recent years. Peptides play a central role as pharmaceuticals and biomaterials in these new drug modalities. Although traditional peptide synthesis using chain-elongation from C- to N-terminus is reliable, it produces large quantities of chemical waste derived from protecting groups and condensation reagents, which place a heavy burden on the environment. Here we report an alternative N-to-C elongation strategy utilizing catalytic peptide thioacid formation and oxidative peptide bond formation with main chain-unprotected amino acids under aerobic conditions. This method is applicable to both iterative peptide couplings and convergent fragment couplings without requiring elaborate condensation reagents and protecting group manipulations. A recyclable N-hydroxy pyridone additive effectively suppresses epimerization at the elongating chain. We demonstrate the practicality of this method by showcasing a straightforward synthesis of the nonapeptide DSIP. This method further opens the door to clean and atom-efficient peptide synthesis.

Dynamic rotation of the protruding domain enhances the infectivity of norovirus.

Norovirus is the major cause of epidemic nonbacterial gastroenteritis worldwide. Lack of structural information on infection and replication mechanisms hampers the development of effective vaccines and remedies. Here, using cryo-electron microscopy, we show that the capsid structure of murine noroviruses changes in response to aqueous conditions. By twisting the flexible hinge connecting two domains, the protruding (P) domain reversibly rises off the shell (S) domain in solutions of higher pH, but rests on the S domain in solutions of lower pH. Metal ions help to stabilize the resting conformation in this process. Furthermore, in the resting conformation, the cellular receptor CD300lf is readily accessible, and thus infection efficiency is significantly enhanced. Two similar P domain conformations were also found simultaneously in the human norovirus GII.3 capsid, although the mechanism of the conformational change is not yet clear. These results provide new insights into the mechanisms of non-enveloped norovirus transmission that invades host cells, replicates, and sometimes escapes the hosts immune system, through dramatic environmental changes in the gastrointestinal tract.