Membrane Shape at the Edge of the Dynamin Helix Sets Location and Duration of the Fission Reaction

Abstract

The GTPase dynamin polymerizes into a helical coat that constricts membrane necks of endocytic pits to promote their fission. However, the dynamin mechanism is still debated because constriction is necessary but not sufficient for fission. Here, we show that fission occurs at the interface between the dynamin coat and the uncoated membrane. At this location, the considerable change in membrane curvature increases the local membrane elastic energy, reducing the energy barrier for fission. Fission kinetics depends on tension, bending rigidity, and the dynamin constriction torque. Indeed, we experimentally find that the fission rate depends on membrane tension in vitro and during endocytosis in vivo. By estimating the energy barrier from the increased elastic energy at the edge of dynamin and measuring the dynamin torque, we show that the mechanical energy spent on dynamin constriction can reduce the energy barrier for fission sufficiently to promote spontaneous fission. :

Dynamic remodeling of the dynamin helix during membrane constriction

“…However, this constriction is not homogeneous, which may be linked to the difficulty of propagating the constriction along the length of long helices (12). Third, fission occurs where constriction is the strongest, consistent with previous findings (19). Also, we did not observe any detectable disassembly of the dynamin coat upon GTP hydrolysis, which may question that disassembly is an important step of the fission reaction (23).…”

“…2D, end of kymograph). Thus, fission clearly occurred where the curvature gradient along the tubule axis was highest, as previously proposed (19).…”

Dynamin-related Protein 1 (Drp1) Promotes Structural Intermediates of Membrane Division

“…Together, this suggests that Drp1 binding to GTP causes concentric assembly of Drp1 and that, upon GTP hydrolysis, Drp1 dissociates to smaller subunit forms. Moreover, these GTP-induced Drp1 clusters were also present along the tubes with a similar distribution pattern as dynamin (48,54), suggesting that those sites could represent potential nucleation points for mitochondrial fission. Along these lines, previous work reported that long dynamin scaffolds did not produce membrane scission, whereas GTPase-dependent cycles of assembly and stochastic disassembly of short dynamin scaffolds led to fission (66,75).…”

α-Synuclein – Regulator of Exocytosis, Endocytosis, or Both?

“…In addition, the proposed double-anchor mechanism could influence the tethering of vesicles to the plasma membrane, thereby regulating the likelihood of exocytosis and thus preventing the full collapse of synaptic vesicles [14] ( Figure 3[ 4 5 7 _ T D $ D I F F ] B). For the mechanism of ultrafast endocytosis, it has yet to be understood how membrane fission can occur in a timescale of tens of milliseconds, while normal fission is reported to be in the range of seconds or even tens of seconds [68]. Facilitation by additional factors including actin, endophilins, and membrane lipids has been discussed, raising the question of whether a-synuclein might also be involved in this process ( Figure 3C).…”