Lipid droplets are organelles that store neutral lipids in cells.
They play an important role in the regulation of lipid homeostasis and disease occurrence.
The formation, fusion and growth defects of lipid droplets can lead to metabolic diseases such as obesity, fatty liver, diabetes and The occurrence and development of atherosclerosis
CIDE family proteins (including Cidea, Cideb and Cidec/Fsp27) are a class of lipid droplet binding proteins, which are mainly enriched in lipid droplet contact site (LDCS) and mediate neutral lipids from small lipid droplets.
The transfer of (donor) to large lipid droplets (acceptor) to achieve the fusion and enlargement of lipid droplets and promote the storage of neutral lipids in cells is an important regulator of lipid homeostasis
However, the biochemical mechanism of CIDE protein enrichment on LDCS, the internal structure of LDCS and the mechanism that mediates lipid circulation and lipid droplet fusion are still unclear
On September 10, 2021, Peng Li’s team from Tsinghua University published an online publication in the Journal of Developmental Cell entitled "Cidec produces lipids through gel-like phase separation, which can promote lipid droplet fusion through a disc-like structure" (A gel-like condensation).
of Cidec generates lipid-permeable plates for lipid droplet fusion).
The author found that Cidec, an important protein that regulates lipid droplet fusion, can pass through the gel through biochemistry, cell biology, super-resolution imaging systems, and biophysical modeling methods.
Such special phase separation methods are enriched in LDCS, assemble and form a highly plastic lipid droplet fusion disk structure that allows lipid exchange and transfer between lipid droplets, thereby promoting the transfer of neutral lipids from small lipid droplets to large lipid droplets.
Finally, the fusion growth of lipid droplets and efficient lipid storage are realized
This study first proposed and proved the role of phase separation in organelle interaction and lipid homeostasis regulation
Many studies in the past ten years have shown that protein enrichment on specific subcellular organelles caused by phase separation is a necessary factor for promoting the control of specific complex biological functions
The author first used imaging technology to find that the enrichment of Cidec on LDCS is mainly mediated by the N-terminal homopolyvalent interaction of Cidec.
Then the author purified the Cidec-N protein, which is different from other proteins that can undergo liquid-liquid phase transition.
-N can perform gel-like phase separation in vitro (Figure 1).
Intracellular imaging experiments have further proved the gel-like characteristics of Cidec-N, and also proved that Cidec-N-mediated coagulation Gel-like phase separation is a necessary condition for Cidec to mediate the fusion and growth of lipid droplets (Figure 1).
The author continues to use a variety of imaging techniques and biophysical modeling methods, and found that Cidec assembles through two-dimensional phase separation at the junction of lipid droplets.
Highly plastic lipid droplet fusion disk structure with lipid exchange and transfer: They also found that when the donor lipid droplets gradually shrink during the fusion process, the width (w) of the lipid droplet fusion disk and the lipid permeable area (A) ) Limited by the size of the donor lipid droplets, the thickness (s) remains unchanged (Figure 2)
The author further identified multiple pores randomly distributed in the internal structure of the contact site through electron tomography imaging and super-resolution fluorescence imaging, and the pore size measured by imaging matched the lipid transport ability
Finally, the study also found that the donor lipid droplets may reduce the efficiency of phase separation (reverse phase separation) through the curvature of the donor lipid droplet to limit the enrichment of the CIDE protein at the lipid droplet junction, reduce the structure of the lipid droplet fusion disc, and reduce The speed of lipid transfer and the efficiency of lipid droplet fusion reveal that the synergistic effect of phase separation and reverse phase separation of CIDE protein can effectively control the transfer of neutral lipids and the stability of lipid droplets during the process of lipid droplet fusion (Figure 2)
In summary, this study reveals that membrane-limited Citec two-dimensional phase separation is the basis for lipid droplet interaction, lipid droplet fusion disc structure formation and lipid droplet fusion, and points out that this type of membrane-bound two-dimensional phase separation may also be involved.
It guides important cell biological processes such as organelle interaction, membrane fusion, exchange of organelle contents, or molecular transport
This allows us to once again see the wide range of biological functions exhibited by protein phase separation
Lu Xuchao, Dr.
Wang Jia, and PhD student Wang Jianqin from the School of Life Sciences of Tsinghua University are the co-first authors of the paper.
Professor Li Peng and the young researcher Chen Fengrong of the Institute of Metabolism and Integrative Biology of Fudan University are the co-corresponding authors
Professor Thorsten Wohland of the National University of Singapore, Professor Long Mian of the Institute of Mechanics of the Chinese Academy of Sciences, Associate Professor Li Pilong of Tsinghua University, Professor Wang Shiqiang, Professor Sun Yujie and Professor Chen Xiaowei of Peking University provided important technical support for this research
This research was supported by the State Key Laboratory of Membrane Biology, Tsinghua-Peking University Joint Center for Life Sciences, Tsinghua University Facility Protein Cryo-electron Microscopy Platform, as well as funding from the National Key Research and Development Program and the National Natural Science Foundation of China
Fluorescent bleaching recovery image of purified Cidec-N-GFP and FUS-GFP droplets in vitro; Cidec-GFP and hnRNPDL(IDR)-Cidec-GFP proteins (green) mediate the fusion of lipid droplets (red) in cells Fluorescence image with growth
Schematic diagram of the lipid droplet fusion disc and its shape characteristics; the model shows that Cidec phase separation and reverse phase separation mediate the assembly and disassembly of lipid permeable discs
Original link: https://doi.