Supplementary Components1. by transferring it towards the ER for metabolic recycling. Launch The endoplasmic reticulum (ER) carries out a multiplicity of functions, including protein and lipid synthesis, lipid metabolism and Ca2+ storage for intracellular signaling. While membranes of the ER are functionally connected to all membranes of the secretory and endocytic pathways via vesicular transport, they only fuse with each other and with vesicles involved in retrograde transport to this organelle. However, close appositions between the ER and the membranes of all other membranous organelles, including the plasma membrane (PM), play major roles in cellular physiology. For example, ER membrane contact sites are involved in the control of Ca2+ homeostasis, in exchanges of lipids between bilayers, and in TRADD the function of ER-localized enzymes that take action and in a Ca2+-dependent way, via its C2 domains (Fig. 2a). Open in a separate window Physique 2 E-Syt1 is a Ca2+-dependent lipid transfer protein(a) Schematics showing the lipid transfer assay. Donor liposomes [PC, DGS-NTA(Ni), NBD-PE], and acceptor liposomes [PC, PS, PI(4,5)P2] were incubated with histidine (His)-tagged cytosolic portion of E-Syt1 protein (E-Syt1cyto). Dequenching of self-quenched NBD-PE fluorescence, i.e. BMH-21 transfer of the fluorescent lipids from donor to acceptor liposomes, was monitored using a fluorometer (observe methods). (b) Structure of NBD-PE. (c) Time-course of normalized fluorescence signals from liposomes mixtures made up of 1% NBD-PE in the donor liposomes at the indicated concentration of Ca2+ in the assay buffer. E-Syt1cyto was added at time 0. (d) Time-course of normalized fluorescence signals from E-Syt1cyto/liposome mixtures made up of different moles percent of NBD-PE in the donor liposomes and incubated with 100M Ca2+. (e) (top) Time-course of turbidity of the suspension (observe methods). Turbidity displays liposome clustering due to tethering of donor and acceptor liposomes. (bottom) Time-course of normalized fluorescence signals from liposome mixtures made up of 1% NBD-PE within the donor liposomes and either E-Syt1cyto or E-Syt1cyto missing the SMP domains (E-Syt1cyto SMP). (f) Style of mutant SMP domains faulty in lipid harboring. Hydrophobic proteins coating the deep hydrophobic groove22 had been mutated to tryptophan (W), hence creating steric hindrance to gain access to of acyl stores towards the SMP route. Aromatic bands of tryptophan are proven as surface area representation. (g) Lipid-binding of E-Syt1 SMP domains. (best) Purified WT SMP BMH-21 domains (Ctrl) and mutant SMP BMH-21 domains, having V169W and L308W mutations (Mut), had been incubated with NBD-PE, operate on native-PAGE and analyzed by fluorometry and blue staining coomassie; (bottom level) Quantification of fluorescence indicators of NBD-PE normalized to the quantity of proteins (indicate +/? SEM, n=3 unbiased experiments; two-tailed Learners t-test with identical variance, P=0.0028). (h) (best) Time-course of turbidity from the suspension system. (bottom level) Time-course of normalized fluorescence indicators from liposome mixtures filled with 1% NBD-PE within the donor liposomes and either E-Syt1cyto or E-Syt1cyto with lipid-binding deficient SMP domains (E-Syt1cyto SMPmut). The transfer of NBD-PE is a lot decreased with E-Syt1cyto SMPmut. For all the liposome-based assays, data are from one experiment; three experiments that yielded related results were performed In the absence of E-Syt1cyto, NBD-PE was self-quenched in the donor liposomes, and solubilization of the liposomes with n-dodecyl–D-maltoside (DDM) resulted in an efficient dequenching (Supplementary Fig. 2a). Addition of E-Syt1cyto and of various Ca2+ concentrations (5 to 200M) to the donor plus acceptor liposomes combination induced quick dequenching of NBD-PE in Ca2+ -dependent manner, consistent with the transfer of NBD-PE from donor to acceptor liposomes (Fig. 2c,d). 1% fluorescent lipids and 100M Ca2+ were used in subsequent transfer assays. Absence of PI(4,5)P2 in the acceptor liposomes drastically slowed the dequenching of NBD-PE (Supplementary Fig. 2b). Furthermore, lipid transfer was bidirectional, as incorporating NBD-PE in either the ER-like or the PM-like liposomes, i.e. reverting donor and acceptor liposomes, resulting in dye dequenching with the same effectiveness (Supplementary Fig. 2c). NBD-PE dequenching was not due to membrane fusion as a similar assay in which the fluorescent lipid tag in the donor liposomes was replaced by a water-soluble luminal self-quenching dye (Sulphorhodamine B) exposed no content combining of the liposomes (Supplementary Fig. 2d). Potential lipid combining due to hemifusion as a result of liposome tethering was ruled out: as exposed by turbidity assay, the potent liposome tethering produced by E-Syt1cyto could be completely reversed by the addition of a cocktail of EDTA,.