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SummaryDynamin is essential for clathrin-dependent coated vesicle formation. It is required for membrane budding at a late stage during the transition from a fully formed pit to a pinched-off vesicle. Dynamin may also fulfill other roles during earlier stages of vesicle formation. We have screened about 16,000 small molecules and have identified 1, named here dynasore, that interferes in vitro with the GTPase activity of dynamin1, dynamin2, and Drp1, the mitochondrial dynamin, but not of other small GTPases. Dynasore acts as a potent inhibitor of endocytic pathways known to depend on dynamin by rapidly blocking coated vesicle formation within seconds of dynasore addition. Two types of coated pit intermediates accumulate during dynasore treatment, ∪-shaped, half formed pits and O-shaped, fully formed pits, captured while pinching off. Thus, dynamin acts at two steps during clathrin coat formation; GTP hydrolysis is probably needed at both steps.

Cells convert excess energy into neutral lipids that are made in the endoplasmic reticulum (ER) bilayer. The lipids are then packaged into spherical or budded lipid droplets (LDs) covered by a phospholipid monolayer containing proteins. LDs play a key role in cellular energy metabolism and homeostasis. A key unanswered question in the life of LDs is how they bud off from the ER. Here, we tackle this question by studying the budding of artificial LDs from model membranes. We find that the bilayer phospholipid composition and surface tension are key parameters of LD budding. Phospholipids have differential LD budding aptitudes, and those inducing budding decrease the bilayer tension. We observe that decreasing tension favors the egress of neutral lipids from the bilayer and LD budding. In cells, budding conditions favor the formation of small LDs. Our discovery reveals the importance of altering ER physical chemistry for controlled cellular LD formation.

As someone who likes solving the molecular puzzle of protein complex assembly, I enjoyed reading two back-to-back articles by Scott Emr and colleagues describing the ESCRT-II and ESCRT-III components of the multivesicular body (MVB)-sorting machinery. Not only was the biochemical evidence top notch, it was also firmly grounded on the genetics of the system. These studies, together with the previous identification of ESCRT-I by the same group published in Cell a year earlier, set the basis for all current analyses of MVB formation and function. Thanks to this work, what was once just a tantalizing morphological entity took center stage in studies of the targeting of transmembrane proteins for degradation in lysosomes. Moreover, the ability of the ESCRT complexes to sculpt intraluminal vesicles from the limiting membrane of endosomes turned out to mediate other important biological processes such as membrane scission during cytokinesis and the release of enveloped viruses, thus becoming a paradigm for membrane budding away from the cytosol. This PaperPick refers to "Escrt-III: An Endosome-Associated Hetero-oligomeric Protein Complex Required for MVB Sorting" by M. Babst, D.J. Katzmann, E.J. Estepa-Sabal, T. Meerloo, and S.D. Emr and "Endosome-Associated Complex, ESCRT-II, Recruits Transport Machinery for Protein Sorting at the Multivesicular Body" by M. Babst, D.J. Katzmann, W.B. Snyder, B. Wendland, and S.D. Emr, both published in August, 2002. Finding ESCRTs II and III Markus Babst and David Katzmann talk about how the ESCRT project started and developed in the Emr lab and where ESCRTs have gone from there.