Figure 1. Model of BLOC-dependent cycling of VAMP7 between endosomes and melanosomes. BLOC-1 promotes the formation of STX13-positive tubules emanating from early endosomes. These tubular carriers carry TYRP1 and VAMP7 to immature melanosomes, where VAMP7 promotes membrane fusion. TYRP1 participates in the deposition of melanin in immature stage II and III melanosomes that accompanies the transition to mature stage IV melanosomes. BLOC-3 promotes the formation of VAMP7-positive tubules from mature melanosomes, recruiting Rab38/32, which in turn recruits VARP. VARP binds to SNARE and Longin domains of VAMP7, maintaining this v-SNARE in an inactive conformation. Anterograde machinery is shown in red, retrograde machinery in blue, and the melanin-synthesizing machinery in brown at points where they are active. Where proteins are likely to be passive cargo, they are shown in black.
Figure 1.

Model of BLOC-dependent cycling of VAMP7 between endosomes and melanosomes. BLOC-1 promotes the formation of STX13-positive tubules emanating from early endosomes. These tubular carriers carry TYRP1 and VAMP7 to immature melanosomes, where VAMP7 promotes membrane fusion. TYRP1 participates in the deposition of melanin in immature stage II and III melanosomes that accompanies the transition to mature stage IV melanosomes. BLOC-3 promotes the formation of VAMP7-positive tubules from mature melanosomes, recruiting Rab38/32, which in turn recruits VARP. VARP binds to SNARE and Longin domains of VAMP7, maintaining this v-SNARE in an inactive conformation. Anterograde machinery is shown in red, retrograde machinery in blue, and the melanin-synthesizing machinery in brown at points where they are active. Where proteins are likely to be passive cargo, they are shown in black.

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