Table S1.

Principal model parameters

Symbol	Meaning	Value
${\lambda }_{\text{D}}$	Debye length	0.8 nm*
$A$	Hamaker constant	$8\times {10}^{-21}$ J†
${\lambda }_{\text{sr}}$	Decay length for intermembrane steric-hydration force	0.2 nm‡
$P_0$	Pressure prefactor for intermembrane steric-hydration force	$6\times {10}^{11}$ dyn/cm2‡
$l_p$	Persistence length of uncomplexed SNARE domains	0.6 nm§
—	Contour length of uncomplexed SNARE domains, per residue	0.365 nm§
—	Length of SNARE bundle	10 nm¶
—	Thickness of SNARE bundle	2 nm¶
$T$	Temperature	298 K#

^*Calculated using a physiological salt concentration of 0.15 M.

^†Typical value for lipid bilayers, from ref. 29.

^‡Calculated as the composition weighted mean of the values reported for pure substances from ref. 28. Membranes considered in this study contained 82% PC, 3% PE, and 15% PS, mimicking a typical composition used for in vitro assays (11). We assumed that PS and PE have similar hydration properties.

^§Typical values for unstructured polypeptides, from ref. 7.

^¶Estimated using PyMOL software using PDB ID code 3HD7.

^#The value used for all simulations except for temperature sweep simulations.