Catalyzes the transfer of a geranyl-geranyl moiety from geranyl-geranyl pyrophosphate to both cysteines in Rab proteins with an -XXCC, -XCXC and -CCXX C-terminal. geranylgeranyl diphosphate + L-cysteinyl-[protein] = diphosphate + S-geranylgeranyl-L-cysteinyl-[protein] Binds 1 zinc ion per subunit. Heterodimer of an alpha and a beta subunit. Belongs to the protein prenyltransferase subunit beta family.