Ras (CXXX) and Rab (CC/CXC) prenylation signal sequences are unique and functionally distinct.
Rab proteins typically lack the consensus carboxyl-terminal CXXX motif that signals isoprenoid modification of Ras and other isoprenylated proteins and, instead, terminate in either CC or CXC sequences (C = cysteine, X = any amino acid). To compare the functional relationship between the Ras CXXX and the Rab CC/CXC motifs, we have generated chimeric Ras proteins terminating in Rab carboxyl-terminal CC or CXC sequences. These mutant Ras proteins were not isoprenylated in vitro or in vivo, demonstrating that the CC and CXC sequences alone are not sufficient to replace a CXXX sequence to signal Ras isoprenoid modification. Surprisingly, chimeric Ras/Rab proteins terminating in significant lengths of carboxyl-terminal sequences from Rab1b (7-139 residues), Rab2 (5-151 residues), or Rab3a (12 residues) were also not isoprenylated. These results demonstrate that the sequence requirements for isoprenoid modification of Rab proteins are more complex than the simple tetrapeptide CXXX sequence for isoprenoid modification of Ras proteins and suggest that the Rab geranylgeranyl transferase(s) requires recognition of protein conformation to signal the addition of geranylgeranyl groups. Finally, competition studies demonstrate that a common geranylgeranyl transferase activity is responsible for the modification of Rab proteins terminating in CC or CXC motifs.
Khosravi-Far
R
R
Department of Pharmacology, Lineberger Cancer Center, University of North Carolina, Chapel Hill 27599.
Clark
G J
GJ
Abe
K
K
Cox
A D
AD
McLain
T
T
Lutz
R J
RJ
Sinensky
M
M
Der
C J
CJ
D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008798:Mevalonic Acid / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D015689:Oncogene Protein p21(ras) / Q000235:genetics / Q000378:metabolism*; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D011106:Polyisoprenyl Phosphates / Q000378:metabolism*; D017368:Protein Prenylation; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000378:metabolism*; D012156:Reticulocytes / Q000378:metabolism; D012717:Sesquiterpenes; D014162:Transfection; D014316:Tritium; D020761:rab1 GTP-Binding Proteins; D020693:rab2 GTP-Binding Protein; D020692:rab3 GTP-Binding Proteins
D009419:Nerve Tissue Proteins; D015513:Oncogene Proteins; D011106:Polyisoprenyl Phosphates; D011993:Recombinant Fusion Proteins; D012717:Sesquiterpenes; D014316:Tritium; C004808:farnesyl pyrophosphate; D019204:GTP-Binding Proteins; C061569:RAB1B protein, rat; D015689:Oncogene Protein p21(ras); D020761:rab1 GTP-Binding Proteins; D020693:rab2 GTP-Binding Protein; D020692:rab3 GTP-Binding Proteins; C002963:geranylgeranyl pyrophosphate; D008798:Mevalonic Acid