Direct Visualization of Ebola Virus Fusion Triggering in the Endocytic Pathway

Spence, Jennifer S.; Krause, Tyler B.; Mittler, Eva; Jangra, Rohit K.; Chandran, Kartik

Further highlighting the distinction between EBOV lipid mixing and fusion, we found that GP mutations that abrogated infectivity did not necessarily extend to lipid mixing (Fig. 7) . Although the F535R mutation was shown to reduce the binding of GP2 ectodomains with liposomes (54), we noted that lipid mixing in live cells was unaffected. Additionally, a peptide corresponding to the fusion loop of the L529A/I544A GP mutant was unable to insert into model membranes or promote lipid mixing in a cellfree system (38) . While we likewise found that the L529A/I544A double mutant could not support infection, lipid mixing activity within cells was significantly reduced but not completely inhibited, indicating that the amino acid sequence may behave differently in native GP and in an isolated peptide, much less in an in vitro system. Shallow insertion of the fusion loop may be sufficient to yield lipid mixing in cells, even while failing to interact with the target membrane extensively enough for progression to full fusion pore formation.