Meta-Biol

• Pathways

Vertebrate RAB27 exists in two isoforms, RAB27A and RAB27B, with overlapping but distinct functions in trafficking to melanosomes, secretory granules and platelets (Kondo et al, 2006; Figueiredo et al, 2008; Tarafder et al, 2011; reviewed in Fukuda et al, 2013). Studies in nematodes and vertebrates have identified MADD as a RAB27 GEF required for its activity (Mahoney et al, 2006; Tarafder et al, 2011; Yoshimura et al, 2010). Interaction of RAB27:GDP with its GEFs promotes release of GDP, allowing GTP to bind, and precludes the interaction of RAB27 with GDI and CHM proteins.