Figure 4.

STX2 deletion promotes STX3- and STX4-mediated SNARE complex assembly. Dispersed pancreatic acini from WT or STX2-KO mice were stimulated for 30 minutes with indicated doses of CcK-8, and then subjected to immunoprecipitation with antibodies against (A) STX3 or (B) STX4. Representative blots are shown in the left panels. Band intensity ratios of co-immunoprecipitated Munc18b/c, SNAP23, and VAMP8/2 relative to immunoprecipitated STX3 (A) or STX4 (B) are shown in corresponding right panels, expressed as ± SEM of 3 independent experiments. Five percent “input” controls (50 μg total acini lysates) with densitometric analysis shown in Supplementary Figure 4A-D. (C) STX2 blocks STX3 and STX4 binding to cognate VAMP8 and VAMP2. STX2 is co-expressed with STX3 or STX4 in HEK cells; controls were expression of single STX and GST. HEK lysates were then subjected to pull-down with GST-VAMP8 or GST-VAMP2. Band intensity ratios of precipitated STX2, STX3 and STX4, and co-precipitated STX2/STX3, and STX2/ STX4 relative to the 5% inputs are shown in corresponding right panels, expressed as mean ± SEM of 3 independent experiments. *P < .05; **P < .01.