Rab proteins geranylgeranyltransferase component A 1 (CHM)

Substrate-binding subunit of the Rab geranylgeranyltransferase (GGTase) complicated. Binds unprenylated Rab proteins and presents the substrate peptide to the catalytic part B composed of RABGGTA and RABGGTB, and remains bound to it after the geranylgeranyl transfer response.

The component A is believed to be regenerated by shifting its prenylated Rab back to the donor membrane. In any case, a pre-formed complex comprising CHM and the Rab GGTase dimer (RGGT or component B) can bind to and prenylate Rab proteins; this alternate pathway is proposed to be the predominant pathway for Rab protein geranylgeranylation.