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. 2013 Jul 30;110(33):13244–13249. doi: 10.1073/pnas.1307685110

Fig. 4.

Fig. 4.

Consequence of the tension clamp model: LDs become hyperreactive. (A) Relative number of nanodroplets and surface tension for LDs with various PL concentrations. After separation from buffer drops, the nanodroplets were counted for various PL/TAG ratios (Fig. S3). The result was normalized to the maximum value at PL/TAG = 2% (left y axis). The surface tensions of the LDs were also measured by micropipette aspiration (right y axis, Fig. S5). COPI efficiency is optimal at vanishing surface tension (fully packed phospholipid monolayer) and very limited when the surface tension increases over a few millinewtons per meter (low PL packing). (B) Using the microfluidic setup developed in Fig. S1, we form buffer drops containing only GFP-labeled α-synuclein (11 nM). (Left) the oil contains 0.02% (wt/wt) PLs or (Right) 0.2% PLs. α-Synuclein binds to the interface for lower PL concentration (<0.03), whereas its binding is abolished for higher PL concentration. (C) Micrometer-scale LDs having low phospholipid packing fuse with bilayer membranes. Optical microscopy picture of LDs incubated with a GUV at PL/TAG ratios below 0.3% shows that LDs efficiently fuse with GUVs and are trapped between the two leaflets of the bilayer (Movie S2). The GUV presented here is 35 µm in diameter. When the PL/TAG ratios are larger than 1%, LDs do not fuse with the GUV membrane. (D) A giant artificial LD (30 µm in diameter, Left) with a PL/TAG ratio close to 0.3% and a fluorescent membrane structure mimicking a neighboring organelle (various curvatures, low surface tension) are brought into contact. Before contact, the LD was not fluorescent. As soon as the membrane touches the LD, they fuse and the membrane spreads around the LD surface (Right), demonstrating the hyperreactivity of the LD. (Insets) The giant LD with an increased contrast to better see the fluorescence. This process is shown in Movie S3. LDs with a PL/TAG ratio larger than 1% did not fuse with the membrane and both entities remained intact after contact for 5 min (Movie S4). (Scale bar, 20 µm.)