(Table S2). bnAb, LN01, which was isolated from lymph-node-derived germinal center B cells of an elite controller and exhibits broad neutralization breadth. LN01 engages both MPER and the transmembrane (TM) region, which together form a continuous helix in complex with LN01. The tilted TM orientation allows LN01 to interact simultaneously with the peptidic component of the MPER epitope and membrane via two specific lipid binding sites of the antibody paratope. Although LN01 carries a high load of somatic mutations, most key residues interacting with the MPER epitope and lipids are germline encoded, lending support for the LN01 epitope as a candidate for lineage-based Tioconazole vaccine development. Keywords: HIV-1, Env, gp41, MPER, broadly neutralizing antibody, LN01, 4E10, 10E8, membrane conversation Graphical Abstract Open in a separate window Highlights ? bNAb LN01 neutralizes 92% of a 118-strain virus panel ? LN01 targets the HIV-1 gp41 MPER, the TM region, and lipids ? LN01-complexed MPER forms a continuous helix with TM ? Most LN01 paratope residues interacting with Tioconazole MPER-TM and lipids are germline encoded The gp41 membrane-proximal Tioconazole external region (MPER) is a highly conserved region of HIV-1 Env. Pinto et?al. characterize the broadly neutralizing anti-MPER mAb LN01, which shows low autoreactivity. LN01 interacts with a complex epitope comprising MPER, the transmembrane region, and lipids, providing insights for vaccine design. Introduction The key to HIV-1 vaccine development is the induction of broadly neutralizing antibodies (bnAbs). The currently known classes of bnAbs target six functional regions around the envelope glycoprotein encompassing the V2 apex, the V3 glycan site, the CD4 binding site, the gp120-gp41 interface region, the gp120 silent face, and the membrane proximal external region (MPER) of Env gp41 (Kwong and Mascola, 2018, Sok and Burton, 2018). MPER-specific bnAbs 4E10, 10E8, DH511, and VRC42 Tioconazole target the same helical linear epitope, which precedes the transmembrane (TM) region (Cardoso et?al., 2005, Huang et?al., 2012, Krebs et?al., 2019, Williams et?al., 2017, Zwick et?al., 2001), and neutralizes more than 90% of multiclade strains (Krebs et?al., 2019, Sok and Burton, 2018). A hallmark of MPER bnAbs are long, heavy-chain CDR3 (HCDR3) loops carrying hydrophobic residues at their tips, whose conversation with membrane is required for neutralization (Alam et?al., 2009, Julien et?al., 2010, Ofek et?al., 2010, Scherer et?al., 2010). MPER bnAbs show various degrees of autoreactivity linked to immune tolerance mechanisms (Chen et?al., 2013, Doyle-Cooper et?al., 2013) that could impair MPER bnAb development. BnAbs 4E10 and VRC42.01 show the most significant non-specific interaction with lipids and membrane (Alam et?al., 2007, Krebs et?al., 2019), while 10E8 and DH511 lineage bnAbs lack important non-specific membrane binding (Huang et?al., 2012, Krebs et?al., 2019, Williams et?al., 2017), indicating that non-specific membrane autoreactivity Rabbit polyclonal to ACSS3 is not a prerequisite of bnAbs targeting MPER. However, specific conversation with membrane is usually important and structures of 4E10 and 10E8 revealed lipid binding of both bnAbs (Irimia et?al., 2016, Irimia et?al., 2017). Based on these structures, models of the Fab-MPER-membrane interface have been generated and have shown that this MPER epitope helix lies nearly perpendicular to the membrane (Irimia et?al., 2016, Irimia et?al., 2017, Rujas et?al., 2016). Although MPER bnAbs 4E10, 10E8, and DH511 recognize the same epitope, their approach angles vary (Williams et?al., 2017). In contrast, VRC42.04 is a close variant of 4E10 that recognizes the same epitope with the same approach angle as 4E10. Interestingly, the latter bnAbs have been independently generated in clade B-and clade CRF016AE-infected patients (Krebs et?al., 2019, Zwick Tioconazole et?al., 2001). MPER epitopes are likely only poorly accessible on native Env trimers, and full epitope accessibility requires at least some degree of receptor/co-receptor-binding-induced conformational changes in Env (Chakrabarti et?al., 2011, Lee et?al., 2016, Rathinakumar et?al., 2012). Consequently, MPER bnAbs bind with high affinity to the fusion intermediate conformation of gp41 (Chen et?al., 2014, Frey et?al., 2008, Lai et?al., 2014). This conformation forms during the receptor-binding-induced transitions from native Env (Pancera et?al., 2014) to the postfusion conformation (Buzon et?al., 2010), thereby facilitating exposure of the linear MPER sequence motif.