Particles were re-extracted without binning and refined against a 30? low-passed filtered 3D class without symmetry. or therapeutics. Murin et al. describe the molecular nature of neutralization by the human survivor pan-ebolavirus antibody ADI-15878. Their structures collectively provide a blueprint that can aid in the development of more potent pan- ebolavirus therapeutics. Graphical Abstract INTRODUCTION There has been a resurgence of Cruzain-IN-1 efforts to develop treatments and vaccines for Ebola virus disease (EVD) after the recent pandemic in western Africa, from 2013C2016. Monoclonal antibodies (mAbs) are at the forefront of therapeutic development since showing great promise in animal models. A tri-mAb cocktail, ZMapp, is being evaluated in clinical trials after demonstrating the ability to revert advanced EVD in non-human primates and showing modest success in Cruzain-IN-1 a small number of patients infected in the aforementioned outbreak (Prevail II Writing Group et al., 2016; Qiu et al., 2014). One disadvantage of ZMapp and similar antibodies is their limited cross-reactivity to other ebolavirus species (Murin et al., 2014). In addition to Ebola virus (EBOV), there are four other species of ebolaviruses that are antigenically divergent, differing by at least 30% on the amino acid level, including Sudan virus (SUDV), Bundibugyo virus (BDBV), Reston virus (RESV), and Tai Forest virus (TAFV). Historically, EBOV, BDBV, and SUDV have caused highly virulent outbreaks in human populations (Burket al., Rabbit polyclonal to FAR2 2016). Ebolaviruses are part of the larger filovirus family, which also includes Marburg virus (MARV) of the marburgvirus genus. MARV has also caused several large human outbreaks, with high lethality (Centers for Disease Control and Prevention, 2014). Given the great unpre dictability and serious nature of ebolavirus outbreaks, a more ideal therapeutic would be one that could target any filovirus with equal potency. The primary target of anti-ebolavirus mAbs is the viral glycoprotein (GP), which is the only protein attached to the viral surface and is indispensable for the viral life cycle (Lee et al., 2008). The viral GP acts as a machine, providing the key to unlocking the host cell membrane and gaining entry into target cells. Entry is achieved by storing tightly regulated potential energy within the metastable, pre-fusion GP, which is released after interaction with the host receptor NPC1, as well as other downstream events that are not well understood (Lee and Sa- phire, Cruzain-IN-1 2009; Miller et al., 2012; White and Schornberg, 2012). Despite the large antigenic diversity among filoviruses, they share their mechanism of entry via structural and sequence conservation in the fusion machinery (Hunt et al., 2012; Miller et al., 2012; White and Schornberg, 2012). The conserved regions include the receptor binding site (RBS), the IFL, and the HR1 and HR2 regions. Filoviral GPs also possess a variable, unstructured, and heavily glycosylated domain Cruzain-IN-1 called the mucin-like domain (MLD), which is thought to be loosely positioned above ebolavirus GPs and draped over the sides of marburgvirus GPs (Hashiguchi et al., 2015). Below the MLDs in ebolaviruses is the glycan cap, which is structured and inserts itself into the RBS (Lee et al., 2008), while in the marburgviruses the analogous region is unstructured, leaving the RBS exposed on GP12,13. The RBS interacts with the host receptor NPC1 during entry and is structurally conserved across all filoviruses (Wang et al., 2016). While the RBS has been shown to elicit pan-filoviral antibodies, potency and efficacy is variable because the ebolaviruses require the proteolytic removal of the MLDs and glycan cap to expose the RBS (Bale et al., 2011; Bornholdt et al., 2016a; Miller et al., 2012; Wang et al., 2016), while the marburgviruses do not (Flyak et al., 2015; Gnirss et al., 2012; King et al., 2018). The HR2 domain has also been proposed as a hotspot of filoviral vulnerability (Flyak et al., 2016, 2018; Wec et al., 2017; Ya- mayoshi and Kawaoka, 2017), but antibodies that target this region have limited cross-reactivity. The HR1 and IFL on filoviral GPs are highly conserved in sequence and structure across genera, as demonstrated by comparing the structures of EBOV, SUDV, and MARV GPs, making this epitope an attractive target for therapeutic antibody development (Bale et al., 2012; Dias et al., 2011; Hashiguchi et al., 2015; King et al., Cruzain-IN-1 2018; Lee et al., 2008; Zhao et al., 2016). HR1 is composed of an alpha helix, which cradles.