Rab geranylgeranyltransferase
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![Crystallographic structure of rat RabGGTase (alpha subunit = green, beta subunit = slate blue, calcium ions are shown as green balls, zinc ion as a blue ball).[1]](/Images/godic/202502/05/Chains_and_Ions2534.png")
Rab geranylgeranyltransferase also known as geranylgeranyltransferase II is one of the three prenyltransferases. It transfers (usually) two geranylgeranyl groups to the cystein(s) at the C-terminus of Rab proteins.
The C-terminus of Rab proteins varies in length and sequence and is referred to as hypervariable. Thus Rab proteins do not have a consensus sequence, such as the CAAX box, which the Rab geranylgeranyltransferase can recognise. Instead Rab proteins are bound by the Rab escort protein (REP) over a more conserved region of the Rab protein and then presented to the Rab geranylgeranyltransferase.