laboratoire de physique statistique
 
 
laboratoire de physique statistique

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ELIFE 


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2016
Seipin is required for converting nascent to mature lipid droplets - Wang, Huajin and Becuwe, Michel and Housden, Benjamin E. and Chitraju, Chandramohan and Porras, Ashley J. and Graham, Morven M. and Liu, Xinran N. and Thiam, Abdou Rachid and Savage, David B. and Agarwal, Anil K. and Garg, Abhimanyu and Olarte, Maria-Jesus and Lin, Qingqing and Froehlich, Florian and Hannibal-Bach, Hans Kristian and Upadhyayula, Srigokul and Perrimon, Norbert and Kirchhausen, Tomas and Ejsing, Christer S. and Walther, Tobias C. and Farese, Jr., Robert V.
ELIFE 5 (2016)

Abstract : How proteins control the biogenesis of cellular lipid droplets (LDs) is poorly understood. Using Drosophila and human cells, we show here that seipin, an ER protein implicated in LD biology, mediates a discrete step in LD formation-the conversion of small, nascent LDs to larger, mature LDs. Seipin forms discrete and dynamic foci in the ER that interact with nascent LDs to enable their growth. In the absence of seipin, numerous small, nascent LDs accumulate near the ER and most often fail to grow. Those that do grow prematurely acquire lipid synthesis enzymes and undergo expansion, eventually leading to the giant LDs characteristic of seipin deficiency. Our studies identify a discrete step of LD formation, namely the conversion of nascent LDs to mature LDs, and define a molecular role for seipin in this process, most likely by acting at ER-LD contact sites to enable lipid transfer to nascent LDs.
 
2015
Re-visiting the trans insertion model for complexin clamping - Krishnakumar, Shyam S. and Li, Feng and Coleman, Jeff and Schauder, Curtis M. and Kuemmel, Daniel and Pincet, Frederic and Rothman, James E. and Reinisch, Karin M.
ELIFE 4 (2015)

Abstract : We have previously proposed that complexin cross-links multiple pre-fusion SNARE complexes via a trans interaction to function as a clamp on SNARE-mediated neurotransmitter release. A recent NMR study was unable to detect the trans clamping interaction of complexin and therefore questioned the previous interpretation of the fluorescence resonance energy transfer and isothermal titration calorimetry data on which the trans clamping model was originally based. Here we present new biochemical data that underscore the validity of our previous interpretation and the continued relevancy of the trans insertion model for complexin clamping.
 
2014
Arf1/COPI machinery acts directly on lipid droplets and enables their connection to the ER for protein targeting - Wilfling, Florian and Thiam, Abdou Rachid and Olarte, Maria-Jesus and Wang, Jing and Beck, Rainer and Gould, Travis J. and Allgeyer, Edward S. and Pincet, Frederic and Bewersdorf, Joerg and Farese, Jr., Robert V. and Walther, Tobias C.
ELIFE 3 (2014)

Abstract : Lipid droplets (LDs) are ubiquitous organelles that store neutral lipids, such as triacylglycerol (TG), as reservoirs of metabolic energy and membrane precursors. The Arf1/COPI protein machinery, known for its role in vesicle trafficking, regulates LD morphology, targeting of specific proteins to LDs and lipolysis through unclear mechanisms. Recent evidence shows that Arf1/COPI can bud nano-LDs (similar to 60 nm diameter) from phospholipid-covered oil/water interfaces in vitro. We show that Arf1/COPI proteins localize to cellular LDs, are sufficient to bud nano-LDs from cellular LDs, and are required for targeting specific TG-synthesis enzymes to LD surfaces. Cells lacking Arf1/COPI function have increased amounts of phospholipids on LDs, resulting in decreased LD surface tension and impairment to form bridges to the ER. Our findings uncover a function for Arf1/COPI proteins at LDs and suggest a model in which Arf1/COPI machinery acts to control ER-LD connections for localization of key enzymes of TG storage and catabolism.
Common intermediates and kinetics, but different energetics, in the assembly of SNARE proteins - Zorman, Sylvain and Rebane, Aleksander A. and Ma, Lu and Yang, Guangcan and Molski, Matthew A. and Coleman, Jeff and Pincet, Frederic and Rothman, James E. and Zhang, Yongli
ELIFE 3 (2014)

Abstract : Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) are evolutionarily conserved machines that couple their folding/assembly to membrane fusion. However, it is unclear how these processes are regulated and function. To determine these mechanisms, we characterized the folding energy and kinetics of four representative SNARE complexes at a single-molecule level using high-resolution optical tweezers. We found that all SNARE complexes assemble by the same step-wise zippering mechanism: slow N-terminal domain (NTD) association, a pause in a force dependent half-zippered intermediate and fast C-terminal domain (CTD) zippering. The energy release from CTD zippering differs for yeast (13 k(B)T) and neuronal SNARE complexes (27 k(B)T), and is concentrated at the C-terminal part of CTD zippering. Thus, SNARE complexes share a conserved zippering pathway and polarized energy release to efficiently drive membrane fusion, but generate different amounts of zippering energy to regulate fusion kinetics.