Table 1.

Parameters used in the analytical model of fusion pores. (A) Measured by fitting a cylinder to the part of the fully zippered SNARE protein structure without the TMDs, produced using PyMOL software with PDB code 3HD7 (http://www.pymol.org). (B) Estimated in this study as a fitting parameter. (C) Measured by Mitra et al. (2004). (D) Measured in this study (Figure 1). (E) Calculated using a weighed average of the ${\text{P}}_0$ of palmitoyl-2-oleoyl phosphatidylcholine (POPC) and 1,2-dioleoyl phosphatidylserine (DOPS) from Rand and Parsegian (1989). The weighed average of the two pressure parameters, according to the 85:15 molar ratio of POPC:DOPS present in the NLPs in this study, is used to obtain ${\text{P}}_0$. We assumed that the hydration properties of POPC are the same as those of 1,2-dioleoyl phosphatidylcholine (DOPC). (F) Values of ${\displaystyle \kappa }$ in previous studies range from 10–50 $\text{kT}$ (Cohen and Melikyan, 2004; Brochard and Lennon, 1975; Khelashvili et al., 2013; Marsh, 2006). A commonly used value in studies is ${\displaystyle \kappa =20\text{kT}}$ (Jackson, 2009), which we used here. (G) Calculated on the basis of an atomistic molecular dynamics study of the t-SNARE TMD, which shows that these domains explore angles of ~${10}^0$ around their equilibrium position in a bilayer (Knecht and Grubmüller, 2003).

DOI: http://dx.doi.org/10.7554/eLife.22964.022

Symbol	Meaning	Value	Legend
${\displaystyle \mathrm{b}}$	Thickness of SNARE bundle	2 nm	(A)
${\displaystyle {\epsilon }_{\text{zip}}}$	Energy of zippering of v- and t-SNAREs	9.6 kT	(B)
${\displaystyle \delta }$	Thickness of the plasma membrane	5 nm	(C)
$\text{D}$	NLP diameter	24 nm	(D)
${\displaystyle \lambda }$	Decay length for inter-membrane steric-hydration force	0.10 nm	(B)
${\text{P}}_0$	Pressure prefactor for inter-membrane steric-hydration force	5.0 × 1011 dyn/cm2	(E)
${\displaystyle \tau }$	Torque per unit length to twist the ApoE proteins at the NLP boundary	$8.43$ pN	(B)
${\displaystyle \kappa }$	Bending modulus of the lipid bilayer	20 kT	(F)
${\displaystyle \gamma }$	Membrane tension	0.66 pN nm−1	(B)
${\displaystyle {\mathrm{\Omega }}_{\text{z}}}$	Solid angle explored by bending of zippered SNAREs	0.05 sr	(G)