Antigenic Variation Of Norovirus GII.4 Strain's VP1 Protein And Its Interaction With VP2 Protein

Norovirus?NOV?is a causative agent of acute gastroenteritis,and the GII.4 genotype of norovirus is the most prevalent virus strain in the world.Recent studies have shown that the mutation of the main capsid protein VP1 is an important factor to escape immunity of GII.4 strain.At present,most studies focus on the main capsid protein?VP1?,but the function and variation mechanism of minor capsid protein?VP2?are unclear.Firstly,with Den_Haag₂006b,New_Orleans₂009 and Sydney₂012 as the main research objects,the VP1 of every strain was expressed systematically.Monoclonal antibodies were constructed to identify the key amino acid sites for immune escape.These results further elucidate the molecular mechanism of GII.4 strain escaping from human herd immunity and lead to periodic pandemics,and provide an important theoretical basis for the design of new vaccine and drugs.On the other hand,by using a human 293 T expression system we investigated the interactions of VP1 and VP2 of three GII.4 strains with focus on the expressional change and cellular allocation.We found that co-transfection of VP1 and VP2 would lead to increase significantly in expressions of both proteins compared to those in the cells transfected with VP1 or VP2 alone.In contrast to the cellular allocation of VP1?with absence of VP2?that was dispersed throughout the cytosol,VP2?with absence of VP1?was found to be allocated in the nuclei that was possibly attributed to a specific nuclear localization signal predicted according to the sequence of the encoding gene.Upon co-transfection of the two proteins,we further found a locational turnover of VP1 expression from in the cytoplasm to being emerged with VP2 co-anchored in the nuclei.These results thus suggest that the VP2 of GII.4 might be functionally and structurally essential to the functional and locational changes of the VP1,and that with cooperation of VP2,VP1 could play a critical role in affecting cell functions via impairing the downstream transcriptional signaling and chromatin remodeling in the cell nuclei.Then we compared and predicted the sequence of VP2 protein by bioinformatics,and found that there was nuclear localization sequence in VP2 protein.The predicted nuclear localization sequence was verified to determine the role of the nucleus-dependent nuclear localization sequence of VP2 protein.These results provide a new idea for the prevention and treatment of norovirus,and suggest that we could develop strategies to prevent norovirus infection by disrupting the combination of VP1 and VP2 or the nuclear entry process.