New insights into BAR domain-induced membrane remodeling - PubMed (original) (raw)

New insights into BAR domain-induced membrane remodeling

Gary S Ayton et al. Biophys J. 2009.

Abstract

Mesoscopic simulations and electron microscopy of N-BAR domain-induced liposome remodeling are used to characterize the process of liposome tubulation and vesiculation. The overall process of membrane remodeling is found to involve complex couplings among the N-BAR protein density, the degree of N-BAR oligomerization, and the membrane density. A comparison of complex remodeled liposome structures from mesoscopic simulations with those measured by electron microscopy experiments suggests that the process of membrane remodeling can be described via an appropriate mesoscopic free energy framework. Liposome remodeling more representative of F-BAR domains is also presented within the mesoscopic simulation framework.

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Figures

Figure 1

Figure 1

(a) Snapshot of a putative N-BAR oligomerization structure on an atomistic membrane. (b) Square slab of EM2 membrane, 250 nm2 in area, and is prepared with a constant N-BAR density and membrane composition. Panels _b_-1–6 follow the membrane through the remodeling process. The arrows designate the local spontaneous curvature directions; the intersecting lines show the local curvature directions on the EM2 membrane.

Figure 2

Figure 2

Tubulation and vesiculation of an EM2 liposome. The N-BAR spontaneous curvature magnitude is given in the far left column, starting from _C_0 = 0.09 nm−1, then _C_0 = 0.10 nm−1, _C_0 = 0.11 nm−1, and _C_0 = 0.15 nm−1. Panel a employs IC, panel b employs CC, panel c uses a combined 50:50 superposition of IC and CC, and panel d is for HC.

Figure 3

Figure 3

A comparison of structures obtained from simulation (left panel) and experimental electron micrographs (right panel). The boxes select out similar structural motifs found in both the simulations and experiment. Density variations in the effective outer leaflet of the EM2 membrane are shown in the smaller images (pink/amber online); where the pink regions have a lower outer bilayer leaflet lipid density. The N-BAR oligomerization fields as given by the EM2 nT vectors are shown in the larger images (blue-white online); darker regions have a relatively larger N-BAR density. In panels a_–_c, IC was used and the oligomerization strength, ΛO, was varied as in Eq. 11. Image c was obtained by removing the mesoscopic solvent after 200 ns of mesoscopic simulation and continuing the simulation in a solvent-free mode. The electron micrographs in panels a and b correspond to endophilin whereas panel c is amphiphysin N-BARs. Virtually indistinguishable tubule diameters were found for both systems.

Figure 4

Figure 4

Final F-BAR tubulation structure from the EM2 model based on Eqs. 1 and 11, with parameters chosen for F-BARs. An initial 500-nm-diameter liposome was used.

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