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Dev Cell. 2019 Nov 18;51(4):488-502.e8. doi: 10.1016/j.devcel.2019.09.019.

Tricalbins Contribute to Cellular Lipid Flux and Form Curved ER-PM Contacts that Are Bridged by Rod-Shaped Structures.

Author information

1
Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
2
Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK; Central Oxford Structural Microscopy and Imaging Centre, South Parks Road, Oxford OX1 3RE, UK.
3
Cell Biology Division, MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK. Electronic address: kukulski@mrc-lmb.cam.ac.uk.

Abstract

Lipid flow between cellular organelles occurs via membrane contact sites. Extended-synaptotagmins, known as tricalbins in yeast, mediate lipid transfer between the endoplasmic reticulum (ER) and plasma membrane (PM). How these proteins regulate membrane architecture to transport lipids across the aqueous space between bilayers remains unknown. Using correlative microscopy, electron cryo-tomography, and high-throughput genetics, we address the interplay of architecture and function in budding yeast. We find that ER-PM contacts differ in protein composition and membrane morphology, not in intermembrane distance. In situ electron cryo-tomography reveals the molecular organization of tricalbin-mediated contacts, suggesting a structural framework for putative lipid transfer. Genetic analysis uncovers functional overlap with cellular lipid routes, such as maintenance of PM asymmetry. Further redundancies are suggested for individual tricalbin protein domains. We propose a modularity of molecular and structural functions of tricalbins and of their roles within the cellular network of lipid distribution pathways.

KEYWORDS:

Extended-Synaptotagmin; correlative light and electron microscopy; cryo-focused ion beam milling; electron cryo-tomography; endoplasmic reticulum; high-throughput yeast genetics; lipid transfer protein; membrane contact sites; plasma membrane; tricalbin

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