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  Liquid-crystalline phase transitions in lipid droplets are related to cellular states and specific organelle association.

Mahamid, J., Tegunov, D., Maiser, A., Arnold, J., Leonhardt, H., Plitzko, J. M., et al. (2019). Liquid-crystalline phase transitions in lipid droplets are related to cellular states and specific organelle association. Proceedings of the National Academy of Sciences of the United States of America, 116(34), 16866-16871. doi:10.1073/pnas.1903642116.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0004-957E-7 Version Permalink: http://hdl.handle.net/21.11116/0000-0004-9582-0
Genre: Journal Article

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 Creators:
Mahamid, J., Author
Tegunov, D.1, Author              
Maiser, A., Author
Arnold, J., Author
Leonhardt, H., Author
Plitzko, J. M., Author
Baumeister, W., Author
Affiliations:
1Department of Molecular Biology, MPI for Biophysical Chemistry, Max Planck Society, ou_1863498              

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Free keywords: cryoelectron tomography; cryofocused ion beam; correlative light and electron microscopy; membrane contact sites; cholesteryl ester
 Abstract: Lipid droplets (LDs) are ubiquitous organelles comprising a central hub for cellular lipid metabolism and trafficking. This role is tightly associated with their interactions with several cellular organelles. Here, we provide a systematic and quantitative structural description of LDs in their native state in HeLa cells enabled by cellular cryoelectron microscopy. LDs consist of a hydrophobic neutral lipid mixture of triacylglycerols (TAG) and cholesteryl esters (CE), surrounded by a single monolayer of phospholipids. We show that under normal culture conditions, LDs are amorphous and that they transition into a smectic liquid-crystalline phase surrounding an amorphous core at physiological temperature under certain cell-cycle stages or metabolic scenarios. Following determination of the crystal lattice spacing of 3.5 nm and of a phase transition temperature below 43 degrees C, we attributed the liquid-crystalline phase to CE. We suggest that under mitotic arrest and starvation, relative CE levels increase, presumably due to the consumption of TAG metabolites for membrane synthesis and mitochondrial respiration, respectively, supported by direct visualization of LD-mitochondrial membrane contact sites. We hypothesize that the structural phase transition may have a major impact on the accessibility of lipids in LDs to enzymes or lipid transporters. These may become restricted in the smectic phase, affecting the exchange rate of lipids with surrounding membranes and lead to a different surface occupancy of LD-associated proteins. Therefore, the composition and the resulting internal structure of LDs is expected to play a key role in their function as hubs of cellular lipid flux.

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Language(s): eng - English
 Dates: 2019-08-022019-08-20
 Publication Status: Published in print
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 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.1073/pnas.1903642116
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Title: Proceedings of the National Academy of Sciences of the United States of America
Source Genre: Journal
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Pages: - Volume / Issue: 116 (34) Sequence Number: - Start / End Page: 16866 - 16871 Identifier: -