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Pinkbar is an epithelial-specific BAR domain protein that generates planar membrane structures


Bin/amphipysin/Rvs (BAR)-domain proteins sculpt cellular membranes and have key roles in processes such as endocytosis, cell motility and morphogenesis. BAR domains are divided into three subfamilies: BAR– and F-BAR–domain proteins generate positive membrane curvature and stabilize cellular invaginations, whereas I-BAR–domain proteins induce negative curvature and stabilize protrusions. We show that a previously uncharacterized member of the I-BAR subfamily, Pinkbar, is specifically expressed in intestinal epithelial cells, where it localizes to Rab13-positive vesicles and to the plasma membrane at intercellular junctions. Notably, the BAR domain of Pinkbar does not induce membrane tubulation but promotes the formation of planar membrane sheets. Structural and mutagenesis analyses reveal that the BAR domain of Pinkbar has a relatively flat lipid-binding interface and that it assembles into sheet-like oligomers in crystals and in solution, which may explain its unique membrane-deforming activity.

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Figure 1: Endogenous Pinkbar associates with membranes in Caco-2 cells and colocalizes with the small GTPase Rab13.
Figure 2: The BAR domain of Pinkbar promotes the formation of planar membrane structures.
Figure 3: Crystal structure and oligomerization of the BAR domain of Pinkbar.
Figure 4: Mechanism of membrane binding and deformation by the BAR domain of Pinkbar.

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This work was supported by the US National Institutes of Health (NIH), National Institute of Mental Health grant MH087950 to R.D. and grants from the Finnish Cancer Foundation and Academy of Finland to P.L. H.Z. was supported by the Academy of Finland, and A.P. and J.S. were supported by fellowships from Viikki Graduate School in Biosciences (VGSB) and Helsinki Graduate Program in Biotechnology and Molecular Biology (GPBM), respectively. Use of the IMCA-CAT beamline 17-BM was supported by the Industrial Macromolecular Crystallography Association through a contract with the Hauptman-Woodward Medical Research Institute. The Advanced Photon Source was supported by Department of Energy Contract W-31-109-Eng-38. We acknowledge A.-L. Nyfors, A. Salminen and A. Strandell for excellent technical assistance.

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A.P., M.B., H.Z., J.S., G.R., M.J., J.H., E.V.K., H.V. and R.D. performed the experiments. A.P., J.P., E.J., M.S., E.I., R.D. and P.L designed and supervised the project. A.P., R.D. and P.L. prepared the manuscript.

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Correspondence to Roberto Dominguez or Pekka Lappalainen.

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The authors declare no competing financial interests.

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Pykäläinen, A., Boczkowska, M., Zhao, H. et al. Pinkbar is an epithelial-specific BAR domain protein that generates planar membrane structures. Nat Struct Mol Biol 18, 902–907 (2011).

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