AUTHOR=Hu Tao , Wu Zhen , Wu Shaoxiong , Wang Mingshu , Jia Renyong , Zhu Dekang , Liu Mafeng , Zhao Xinxin , Yang Qiao , Wu Ying , Zhang Shaqiu , Huang Juan , Mao Sai , Ou Xumin , Gao Qun , Sun Di , Liu Yunya , Zhang Ling , Yu YanLing , Chen Shun , Cheng Anchun TITLE=Substitutions at Loop Regions of TMUV E Protein Domain III Differentially Impair Viral Entry and Assembly JOURNAL=Frontiers in Microbiology VOLUME=12 YEAR=2021 URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.688172 DOI=10.3389/fmicb.2021.688172 ISSN=1664-302X ABSTRACT=

Flavivirus envelope protein (E) plays an important role in cellular infection, especially in virulence and antigenicity. E domain III of Tembusu virus (TMUV) is highly conserved among flaviviruses and contains four loop regions. However, the functions of the loop regions of TMUV E domain III in the viral life cycle have not yet been discovered. In this study, using a reverse genetics system, we performed site-directed mutagenesis on loops I, II, III, and IV of TMUV E domain III. Mutant 6 (S388A.G389A.K390A) showed better proliferation than the wild-type virus, while mutants 1–5 exhibited decreased in vitro infectivity, as determined by immunofluorescence assay (IFA). Based on a TMUV replicon system, the mutations exhibited no apparent effect on TMUV RNA replication. Subcellular fractionation assays and packaging system assays indicated that mutations in loops II–IV (T332A, T332S, S365A.S366A.T367A, and S388A.G389A.K390A, respectively) disrupted virion assembly. Moreover, loops I–IV played an important role in virus binding and entry, while mutant 6 (S388A.G389A.K390A) exhibited robust activity in virus entry. Taken together, our findings indicated the critical role of the loop regions in TMUV E domain III in the virus entry and assembly process.