STRUCTURAL INSIGHTS INTO THE FUNCTION OF THE RAB GDI SUPERFAMILY

The 1.81 Angstrom crystal structure of Rab GDP-dissociation inhibitor (GDI), a protein that plays a critical role in the recycling of Rab GT Pases involved in membrane vesicular transport, has been recently dete rmined. Biochemical studies implicate a highly conserved region involv ed in Rab binding, which is common to both GDI and the evolutionarily- related choroideremia gene product (CHM/REP) required for Rab prenylat ion. Here, we summarize the mechanisms by which members of the GDI sup erfamily might function to coordinate events leading to membrane fusio n, and we discuss the unexpected, yet striking structural homology of GDI to FAD-binding proteins.