title: Deficient geranylgeranylation of Ram/Rab27 in choroideremia.
abstract: Choroideremia, an X-linked form of retinal degeneration, results from defects in the Rab escort protein-1 (REP-1) gene. REP-1 and REP-2 assist in the attachment of geranylgeranyl groups to Rab GTPases, a modification essential for their action as molecular switches regulating intracellular vesicular transport. If Rabs that depend preferentially on REP-1 for prenylation exist, they will accumulate unprenylated in choroideremia cells. Using recombinant Rab geranylgeranyl transferase and REPs to label unprenylated cytosolic proteins, we identified one unprenylated protein in choroideremia lymphoblasts that was prenylated in vitro more efficiently by REP-1 than by REP-2. This protein was purified and identified as Ram (renamed Rab27), a previously cloned Rab of unknown function. Immunohistochemistry of rat retina showed that Ram/Rab27 is expressed in the pigment epithelium and choriocapillaris, the two retinal cell layers that degenerate earliest in choroideremia. These results raise the possibility that the retinal degeneration in choroideremia results from the deficient geranylgeranylation of Ram/Rab27 or a closely related protein.
authors.affiliation: Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75235, USA.
authors.forename: M C
authors.initials: MC
authors.lastname: Seabra
authors.forename: Y K
authors.initials: YK
authors.lastname: Ho
authors.forename: J S
authors.initials: JS
authors.lastname: Anant
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D019883:Alkyl and Aryl Transferases; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000302:isolation & purification; D002460:Cell Line; D015794:Choroideremia / Q000235:genetics* / Q000378:metabolism*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003001:Cloning, Molecular; D017931:DNA Primers; D004926:Escherichia coli; D005260:Female; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008214:Lymphocytes; D008297:Male; D008969:Molecular Sequence Data; D017368:Protein Prenylation; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D014166:Transferases / Q000302:isolation & purification / Q000378:metabolism*; D014960:X Chromosome; D020691:rab GTP-Binding Proteins; D000075745:rab27 GTP-Binding Proteins
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C081787:CHM protein, human; D002352:Carrier Proteins; C513166:Chm protein, rat; D017931:DNA Primers; D011994:Recombinant Proteins; D000075745:rab27 GTP-Binding Proteins; D014166:Transferases; D019883:Alkyl and Aryl Transferases; C075607:Rab geranylgeranyltransferase; D019204:GTP-Binding Proteins; C066694:RAB27A protein, human; C512961:Rab27a protein, rat; D020691:rab GTP-Binding Proteins