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: 32.24). 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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    ABSTRACT: PICK1 is a neuronal scaffolding protein containing a PDZ domain and an auto-inhibited BAR domain. BAR domains are membrane-sculpting protein modules generating membrane curvature and promoting membrane fission. Previous data suggest that BAR domains are organized in lattice-like arrangements when stabilizing membranes but little is known about structural organization of BAR domains in solution. Through a small-angle X-ray scattering (SAXS) analysis, we determine the structure of dimeric and tetrameric complexes of PICK1 in solution. SAXS and biochemical data reveal a strong propensity of PICK1 to form higher-order structures, and SAXS analysis suggests an offset, parallel mode of BAR-BAR oligomerization. Furthermore, unlike accessory domains in other BAR domain proteins, the positioning of the PDZ domains is flexible, enabling PICK1 to perform long-range, dynamic scaffolding of membrane-associated proteins. Together with functional data, these structural findings are compatible with a model in which oligomerization governs auto-inhibition of BAR domain function. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Structure 06/2015; 23(7). DOI:10.1016/j.str.2015.04.020 · 5.62 Impact Factor
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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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    ABSTRACT: Bin-Amphiphysin-Rvs (BAR) domain proteins are central regulators of many cellular processes involving membrane dynamics. BAR domains sculpt phosphoinositide-rich membranes to generate membrane protrusions or invaginations. Here, we report that, in addition to regulating membrane geometry, BAR domains can generate extremely stable lipid microdomains by "freezing" phosphoinositide dynamics. This is a general feature of BAR domains, because the yeast endocytic BAR and Fes/CIP4 homology BAR (F-BAR) domains, the inverse BAR domain of Pinkbar, and the eisosomal BAR protein Lsp1 induced phosphoinositide clustering and halted lipid diffusion, despite differences in mechanisms of membrane interactions. Lsp1 displays comparable low diffusion rates in vitro and in vivo, suggesting that BAR domain proteins also generate stable phosphoinositide microdomains in cells. These results uncover a conserved role for BAR superfamily proteins in regulating lipid dynamics within membranes. Stable microdomains induced by BAR domain scaffolds and specific lipids can generate phase boundaries and diffusion barriers, which may have profound impacts on diverse cellular processes.
    Cell Reports 09/2013; 4(6). DOI:10.1016/j.celrep.2013.08.024 · 8.36 Impact Factor
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    • "Pacsin-1's altered membrane sculpting propensity could be a result of the PRD-SH3 interactions further enabling the arrangement of pacsin-1 into higher-order oligomers on the membrane to facilitate deformation. The formation of oligomers on membranes has been reported in several independent studies conducted on other BAR domain proteins [23], [34], [68]. "
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    ABSTRACT: Endocytosis is a fundamental process in signaling and membrane trafficking. The formation of vesicles at the plasma membrane is mediated by the G protein dynamin that catalyzes the final fission step, the actin cytoskeleton, and proteins that sense or induce membrane curvature. One such protein, the F-BAR domain-containing protein pacsin, contributes to this process and has been shown to induce a spectrum of membrane morphologies, including tubules and tube constrictions in vitro. Full-length pacsin isoform 1 (pacsin-1) has reduced activity compared to its isolated F-BAR domain, implicating an inhibitory role for its C-terminal Src homology 3 (SH3) domain. Here we show that the autoinhibitory, intramolecular interactions in pacsin-1 can be released upon binding to the entire proline-rich domain (PRD) of dynamin-1, resulting in potent membrane deformation activity that is distinct from the isolated F-BAR domain. Most strikingly, we observe the generation of small, homogenous vesicles with the activated protein complex under certain experimental conditions. In addition, liposomes prepared with different methods yield distinct membrane deformation morphologies of BAR domain proteins and apparent activation barriers to pacsin-1's activity. Theoretical free energy calculations suggest bimodality of the protein-membrane system as a possible source for the different outcomes, which could account for the coexistence of energetically equivalent membrane structures induced by BAR domain-containing proteins in vitro. Taken together, our results suggest a versatile role for pacsin-1 in sculpting cellular membranes that is likely dependent both on protein structure and membrane properties.
    PLoS ONE 12/2012; 7(12):e51628. DOI:10.1371/journal.pone.0051628 · 3.23 Impact Factor
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