Fig. 3: Membrane-binding decreases MreB filament twist and induces membrane curvature.
From: Chiral twisting in a bacterial cytoskeletal polymer affects filament size and orientation
a Simulated system of a 4 × 2 MreB double protofilament in water. The system consists of four MreB doublets (eight subunits), surrounded by a water box. b Distribution of twist angles in simulated systems at equilibrium. The ATP-bound 4 × 2 protofilament displayed a large twist angle, which decreased when the 4 × 2 protofilament bound the membrane. Membrane binding did not substantially affect the twist angle of ADP-bound protofilaments. Solid dots are histograms from the last 40 ns (200 frames) of each simulation, and curves are Gaussian fits of the histograms. c The twist angles for ATP- and ADP-MreB in (b) remained stable and easily distinguished between the two nucleotide-binding states in simulations longer than 500 ns. d Twist angles decreased over time when a pre-twisted 4 × 2 protofilament was placed close to a membrane patch. Untwisting occurred first in Pair 3, then propagated to Pair 2 and Pair 1. The dashed line shows the initial twist angle in Pair 2. e Buried SASA of the membrane-binding interface for the twisted protofilament. Higher buried SASA indicates stronger membrane interaction. Similar to the changes in twist angles, the buried SASA increased first in Pair 3, then in Pair 2 and Pair 1. The dashed line is the initial buried SASA for Pair 2. f Scatter plot of buried SASAs and twist angles in the simulation analyzed in (d, e). Each dot represents the values for a certain pair at a particular time point, and dashed lines are the initial values for Pair 2. Buried SASA and twist angle were highly correlated (Pearson’s r = 0.79, p < 10−10, Student’s t test). g In a typical membrane simulation with 4 × 2 protofilaments, the membrane started flat (top) and ended up curved toward MreB (bottom). h Values of induced membrane curvature in 4 × 2 and 4 × 1 protofilament simulations. Only the 4 × 2 protofilaments induced non-zero membrane curvatures. The dashed line represents the in vivo reference value for a rod-shaped cell with width 0.8 µm. Data points represent the mean ± S.D. for the last 40 ns of each simulation.
