biostudies-literatureYamamoto MMEXT | Japan Society for the Promotion of ScienceJapan Agency for Medical Research and DevelopmentMinistry of Education, Culture, Sports, Science and Technology5677-5687https://www.ebi.ac.uk/biostudies/studies/S-EPMC6462516biostudies-literatureUnknown294(14)Membrane fusion is the first essential step in HIV-1 replication. The gp41 subunit of HIV-1 envelope protein (Env), a class I fusion protein, achieves membrane fusion by forming a structure called a six-helix bundle composed of N- and C-terminal heptad repeats. We have recently shown that the distal portion of the α9 helix in the C-terminal heptad repeat of X4-tropic HXB2 Env plays a critical role in the late-stage membrane fusion and viral infection. Here, we used R5-tropic JRFL Env and constructed six alanine insertion mutants, 641+A to 646+A, in the further distal portion of α9 where several glutamine residues are conserved (the number corresponds to the position of the inserted alanine in JRFL Env). 644+A showed the most severe defect in syncytia formation. Decreased fusion pore formatThe Journal of biological chemistryCell-cell and virus-cell fusion assay-based analyses of alanine insertion mutants in the distal α9 portion of the JRFL gp41 subunit from HIV-1.PMC646251618K15235Core-to-Core Program A: Advanced Research Networks16H06575JP18fm0108006Du QTanaka YYamamoto MInoue JIWang HWatanabe AKawaguchi YSong JMatsuda ZfalseCell-cell and virus-cell fusion assay-based analyses of alanine insertion mutants in the distal α9 portion of the JRFL gp41 subunit from HIV-1.Membrane fusion is the first essential step in HIV-1 replication. The gp41 subunit of HIV-1 envelope protein (Env), a class I fusion protein, achieves membrane fusion by forming a structure called a six-helix bundle composed of N- and C-terminal heptad repeats. We have recently shown that the distal portion of the α9 helix in the C-terminal heptad repeat of X4-tropic HXB2 Env plays a critical role in the late-stage membrane fusion and viral infection. Here, we used R5-tropic JRFL Env and constructed six alanine insertion mutants, 641+A to 646+A, in the further distal portion of α9 where several glutamine residues are conserved (the number corresponds to the position of the inserted alanine in JRFL Env). 644+A showed the most severe defect in syncytia formation. Decreased fusion pore format2019-01-01T00:00:00Z2019 Apr2026-04-28T21:53:44.07Z2020-10-04T07:07:01ZS-EPMC64625163073727810.1074/jbc.RA118.00457910.1074/jbc.ra118.004579