Membrane shaping by the Bin/amphiphysin/Rvs (BAR) domain protein superfamily

Abstract

BAR domain superfamily proteins have emerged as central regulators of dynamic membrane remodeling, thereby playing important roles in a wide variety of cellular processes, such as organelle biogenesis, cell division, cell migration, secretion, and endocytosis. Here, we review the mechanistic and structural basis for the membrane curvature-sensing and deforming properties of BAR domain superfamily proteins. Moreover, we summarize the present state of knowledge with respect to their regulation by autoinhibitory mechanisms or posttranslational modifications, and their interactions with other proteins, in particular with GTPases, and with membrane lipids. We postulate that BAR superfamily proteins act as membrane-deforming scaffolds that spatiotemporally orchestrate membrane remodeling.

Fig. 1

Architecture of BAR domains and their role in membrane deformation. a–e Crystal structures of BAR/N-BAR domains: the arfaptin BAR domain (1I49) (a), the Drosophila melanogaster amphiphysin BAR domain (D-Amph) (1URU) (b), the endophilin III BAR domain (2Z0V) (c), the PX-BAR domain from SNX 9 (3DYT) (d), and the BAR-PH domain from APPL1 (2Q12) (e). f–h Structural insights into F-BAR domain architecture: the F-BAR domains of FBP17 (2EFL) (f), syndapin 1 (2X3X) (g), and yeast Syp1 (3G9G) (h). i Crystal structure of the IRSp53 I-BAR domain (1WDZ). j Membrane deformation by BAR/N-BAR, F-BAR, and I-BAR domains. BAR and F-BAR domains induce positive membrane curvature, whereas I-BAR domains generate negative membrane curvature. Amphipathic α-helices are indicated by red arrows in (b), (c) and (h). The additional amphipathic α-helix within the endophilin BAR domain is indicated by an orange arrow in (c). Crystal structures were generated with Pymol

Fig. 2

Comparison of F-BAR domains. Monomer structures of the F-BAR domains from syndapin 1, FCHo2 (2V0O), CIP4 (2EFK), and FBP17 are shown. The degree of lateral bending was quantified by determining the angle between the long axis of the central 3-helix bundle (concave surface) and the long axis of the lateral helical region

Fig. 3

Biological functions and regulation of BAR domain superfamily proteins. a BAR domain proteins function in the generation of membrane protrusions and membrane invaginations, as well as in vesicle fission. b Regulation of BAR domain proteins. Mechanisms include autoinhibition (a), phosphorylation/dephosphorylation (b), and protein–protein interactions (c). The latter may keep BAR domain proteins in an “inactive” state. c Membrane targeting of BAR domain proteins. Interactions with GTPases aid targeting of some BAR domain proteins to specific membrane sites. See text for further details