Figure 6.

Localization of Munc13-4 on secretory lysosomes required MHDs. GFP-tagged rab27a (green) constructs were cotransfected with His-tagged Munc13-4 in RBL-2H3 cells. Fixed cells were labeled with the EXPRESS antibody for His-Munc13-4 (red). Wild-type rab27a and rab27aQ78L extensively colocalized on the limiting membrane of secretory lysosomes. The rab27aT23N mutant was diffusely distributed throughout the cytoplasm, whereas Munc13-4 is still targeted to secretory lysosomes. Unlike Munc13-4, the GS2 mutant rab27aW73G that poorly bound Munc13-4 did not localize to secretory lysosomes. (A) Transfection of GFP-tagged Munc13-4 truncation constructs (green) in RBL cells. (B) Cells were fixed and labeled with an antibody against serotonin (red). With the exception of Munc13-4(aa 1–543) that included the rab27a binding domain, the truncations localized to secretory lysosomes. Bar, 5 μm