Rab geranylgeranyltransferase

Rab geranylgeranyltransferase, alpha subunit
Crystallographic structure of rat RabGGTase (rainbow colored, N-terminus = blue, C-terminus = red).[1]
Identifiers
Symbol	RABGGTA
NCBI gene	5875
HGNC	9795
OMIM	601905
RefSeq	NM_004581
UniProt	Q92696
Other data
EC number	2.5.1.60
Locus	Chr. 14 q11.2
Search for Structures Swiss-model Domains InterPro

Rab geranylgeranyltransferase also known as (protein) 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.^[2]

geranylgeranyl diphosphate + protein-cysteine ${\displaystyle \rightleftharpoons }$ S-geranylgeranyl-Cys-protein + diphosphate

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.

Once Rab proteins are prenylated, the lipid anchor(s) ensure that Rabs are no longer soluble. REP therefore plays an important role in binding and solubilising the geranylgeranyl groups and delivers the Rab protein to the relevant cell membrane.