Binds unprenylated Rab proteins, presents it to the catalytic Rab GGTase dimer, and remains bound to it after the geranylgeranyl transfer reaction. The component A is thought to be regenerated by transferring its prenylated Rab back to the donor membrane. Also a pre-formed complex consisting of CHM and the Rab GGTase dimer (RGGT or component B) can bind to and prenylate Rab proteins; this alternative pathway is proposed to be the predominant pathway for Rab protein geranylgeranylation.
Involvement in disease
Defects in CHM are the cause of choroideremia (CHM) [MIM:303100]. An X-linked recessive disease characterized by a slowly progressive degeneration of the choroid, photoreceptors, and retinal pigment epithelium. Affected males develop night blindness in their teenage years followed by loss of peripheral vision and complete blindness at middle age. Carrier females are generally asymptomatic but funduscopic examination often shows patchy areas of chorioretinal atrophy.