FIGURE 10:

In the presence of Sec18 and MgATP, fusion of R+Qa proteoliposomes remains sensitive to the Jx swap, and reversal of this block by Sec17 requires its hydrophobic loop. With membrane-anchored Qb, there is less fusion inhibition by the Jx swap, with little effect of Sec17 or its hydrophobic loop. Proteoliposomes were prepared as described in Figure 6, with either one or two anchored Q-SNAREs. Fusion reactions were conducted as described in Materials and Methods with 50 nM HOPS, 100 nM Qc, 100 nM sQb (where Qa was the only anchored SNARE), 500 nM Sec17 or Sec17 FSMS where added, and with 250 nM Sec18 and 1 mM hydrolyzable MgATP. Averages and SDs of fusion rates from minutes 0–20 are shown from three replicate experiments. Typical kinetic data are shown in Supplemental Figure S6.