Module 2: Figure Rab signalling
Function of the Rab monomeric G-protein in cell signalling
The monomeric Rab G-protein is regulated at a number of levels. Newly synthesized Rab bound to GDP is recognized by the Rab escort protein (REP), which presents it to the geranylgeranyl transferase (GGT). GGT adds geranylgeranyl groups to one or two of the C-terminal cysteine residues. The geranylgeranylated Rab is recognized by the Rab GDP dissociation inhibitor (GDI), which operates the Rab membrane cycle. The Rab.GDP is then targeted to specific membrane sites by interacting with the GDI displacement factor (GDF). Various guanine nucleotide-exchange factors (GEFs) and GTPase-activating proteins (GAPs) operate the Rab GTP/GDP cycle responsible for the inter-conversions between inactive Rab.GDP and active Rab.GTP. The latter then acts on a variety of effectors to regulate many of the processes responsible for protein trafficking.