Article

Structural Basis of Membrane Bending by the N-BAR Protein Endophilin

Department of Molecular Biosciences, Northwestern University, 2205 Campus Drive, Evanston, IL 60208, USA.
Cell (Impact Factor: 33.12). 03/2012; 149(1):137-45. DOI: 10.1016/j.cell.2012.01.048
Source: PubMed

ABSTRACT Functioning as key players in cellular regulation of membrane curvature, BAR domain proteins bend bilayers and recruit interaction partners through poorly understood mechanisms. Using electron cryomicroscopy, we present reconstructions of full-length endophilin and its N-terminal N-BAR domain in their membrane-bound state. Endophilin lattices expose large areas of membrane surface and are held together by promiscuous interactions between endophilin's amphipathic N-terminal helices. Coarse-grained molecular dynamics simulations reveal that endophilin lattices are highly dynamic and that the N-terminal helices are required for formation of a stable and regular scaffold. Furthermore, endophilin accommodates different curvatures through a quantized addition or removal of endophilin dimers, which in some cases causes dimerization of endophilin's SH3 domains, suggesting that the spatial presentation of SH3 domains, rather than affinity, governs the recruitment of downstream interaction partners.

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    • "The helix mode based on the arrangement of endophilin BAR domains on tubules (Mim et al., 2012) also yielded good fits to the experimental data, although inferior to the fits from the offset mode (Figure 6B). On the other hand, the tip-to-tip, side-byside , and circle mode produced substantially worse fits (Figures 10Å A "
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    • "It is, however, also important to note that the self-assembly mechanisms of N-BAR and F-BAR domains are different. Protein scaffolds formed by endophilin N-BAR domain are held together through interactions between endophilin's amphipathic N-terminal helices, whereas the F-BAR domain scaffolds are stabilized through lateral contacts between the coiled-coil regions of the domains (Frost et al., 2008; Mim et al., 2012). Importantly, membrane insertion of the N-terminal a helix of Rvs161/167, endophilin, and amphiphysin BAR domains is enhanced by PI(4,5)P 2 (Figures S3E and S3F; Yoon et al., 2012), demonstrating that, in addition to the coiled-coil region, also the N-terminal helix contributes to phosphoinositide specificity of N- BAR domains. "
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    • "The highest membrane curvature at the Golgi is found at the neck of a growing vesicle. Arfaptin-1 has thus a tropism for the vesicle neck (Habermann, 2004), and has the potential to stabilize it by forming a scaffold that prevents membrane fission (Boucrot et al., 2012; Mim et al., 2012). Shedding of such a scaffold would not only physically destabilize the vesicle neck, but would subsequently allow access for the scission complex. "
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