Rab Geranylgeranylation occurs preferentially via the pre-formed REP:RGGT complex and is regulated by geranylgeranyl pyrophosphate

Rudi A. Baron , Miguel C Seabra (1)

1 Molecular Medicine, NHLI

Prenylation (or Geranylgeranylation, GG) of Rab GTPases is catalysed by Rab Geranylgeranyl Transferase (RGGT) and requires Rab Escort Protein (REP). In the classical pathway, REP associates first with unprenylated Rab which is then prenylated by RGGT. In the alternative pathway, REP associates first with RGGT; this complex then binds and prenylates Rab proteins. Here we show that REP mutants (REP1F282L and REP1F282L/V290F) defective in RGGT binding are unable to compete with wild-type REP in the prenylation reaction in vitro. When over-expressed in cells, REP wild type and mutants are unable to form stable cytosolic complexes with endogenous unprenylated Rabs. These results suggest that the alternative pathway may predominate in vivo. We also extend previous suggestions that GGPP acts as an allosteric regulator of the reaction. We observed that REP:RGGT complexes are formed in vivo and are unstable in absence of intracellular GGPP. RGGT decreases the ability of REP to extract endogenous prenylated Rabs from membranes in vitro by stabilising a soluble REP:RGGT:Rab-GG complex. This effect is regulated by GGPP, which promotes the dissociation of RGGT and REP:Rab-GG to allow delivery of prenylated Rabs to membranes.

Mots clés: Life Sciences

Rudi A. Baron, Miguel C Seabra. Rab Geranylgeranylation occurs preferentially via the pre-formed REP:RGGT complex and is regulated by geranylgeranyl pyrophosphate. Biochemical Journal, 2008, 415 (1), pp.67-75. ⟨10.1042/BJ20080662⟩. ⟨hal-00479003⟩