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. 2023 Jul 14;13(7):1130. doi: 10.3390/biom13071130

Figure 4.

Figure 4

Placental and retroviral fusion protein six-helix bundles (6HBs). The Syncytin-1 (PDB ID: 6RX1) and Syncytin-2 (PDB ID: 6RX3) 6HBs are oriented relative to the placental syncytiotrophoblast membrane (top), while the Mason-Pfizer Monkey Virus (PDB ID: 4JF3) and Avian Rous Sarcoma Virus (PDB ID: 4JPR) 6HBs are shown relative to the infected cell membrane (bottom). Both placental and retroviral proteins form the canonical post-fusion 6HB conformation following receptor recognition and/or pH acidification. Created with Biorender.