Intracellular Vesicle Fusion Requires a Membrane-Destabilizing Peptide Located at the Juxtamembrane Region of the v-SNARE

Rathore, Shailendra S.; Liu, Yinghui; Yu, Haijia; Wan, Chun; Lee, MyeongSeon; Yin, Qian; Stowell, Michael H.B.; Shen, Jingshi

How does the juxtamembrane motif of the v-SNARE destabilize the membrane bilayer? Electron microscopy (EM) imaging showed that the juxtamembrane motif deforms the membrane bilayer, which creates local elastic stresses and reduces the energy barrier for membrane merging McMahon et al., 2010) . Curvature induction usually requires the cooperative action of multiple copies of a membrane-binding molecule (Hui et al., 2009; McMahon et al., 2010) so that the juxtamembrane motif is unable to induce curvature within free v-SNAREs. When multiple SNARE complexes (three or more) zipper cooperatively in a vesicle fusion reaction (Domanska et al., 2009; Mohrmann et al., 2010; Shi et al., 2012) , it is conceivable that their juxtamembrane motifs are concentrated at the fusion sites, allowing curvature induction. This curvature-inducing activity can be recapitulated by adding high concentrations of synthetic juxtamembrane motif peptides ( Figure 5D ). The juxtamembrane peptide of the v-SNARE may also promote dehydration of lipid head groups, which disrupts membrane integrity and neutralizes negative lipid charges to reduce the repulsive force of approaching membranes Murray et al., 1999; Shintou et al., 2007; Tarafdar et al., 2015) . Interestingly, in the postfusion cis-SNARE complex, the juxtamembrane motif associates with the t-SNAREs , suggesting that the juxtamembrane motif is dislodged from the membrane during a late stage of the fusion reaction. It is conceivable that dislodging of the juxtamembrane motif further disrupts the membrane structure at the fusion sites. Before its ultimate pairing with the t-SNAREs, the dislodged juxtamembrane motif may also transiently bind and destabilize the target membrane in trans. Together, these membraneremodeling activities facilitate lipid rearrangements to form stalk and hemifusion intermediates, followed by opening and expansion of fusion pores controlled by SNARE transmembrane domains (Bao et al., 2016; Chang et al., 2015; Dhara et al., 2016; Fang and Lindau, 2014; Lindau et al., 2012; Ngatchou et al., 2010; Pieren et al., 2015) .