Microsomal membranes contain a high affinity binding site for prenylated peptides.
Prenylation and subsequent processing of many proteins involved in cellular signaling serves to direct and/or anchor these proteins to specific membranes in the cell. One major class of prenylated proteins contains the so-called CAAX motif; such proteins contain a cysteine residue fourth from the COOH terminus. After addition of the isoprenoid to this cysteine residue by specific cytosolic protein prenyltransferases, the proteins are subject to further processing by enzymes associated with microsomal membranes. This suggests that newly prenylated proteins are initially directed to a microsomal membrane compartment for completion of their processing. Using a radiolabeled, prenylated peptide as a ligand, we have identified a specific, high affinity binding site or receptor on microsomal membranes. This receptor is both protease- and heat-sensitive and exhibits saturable binding of the prenylated peptide with a KD of 30 nM. Competition analysis indicates that both geranylgeranylated and farnesylated, but not myristoylated, peptides bind to this receptor. A fully processed prenylated protein also does not compete, indicating a role for the three terminal residues of the prenylated peptide in receptor recognition. This receptor may serve to direct newly prenylated proteins to a microsomal compartment for completion of processing prior to trafficking to their final destination in the cell.
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