MICROSOMAL-MEMBRANES CONTAIN A HIGH-AFFINITY BINDING-SITE FOR PRENYLATED PEPTIDES

Prenylation and subsequent processing of many proteins involved in cel lular signaling serves to direct and/or anchor these proteins to speci fic membranes in the cell. One major class of prenylated proteins cont ains the so-called CAAX motif, such proteins contain a cysteine residu e fourth from the COOH terminus. After addition of the isoprenoid to t his 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 protein s are initially directed to a microsomal membrane compartment for comp letion of their processing. Using a radiolabeled, prenylated peptide a s a ligand, we have identified a specific, high affinity binding site or receptor on microsomal membranes. This receptor is both protease- a nd heat-sensitive and exhibits saturable binding of the prenylated pep tide with a K(D) of 30 nM. Competition analysis indicates that both ge ranylgeranylated and farnesylated, but not myristoylated, peptides bin d to this receptor. A fully processed prenylated protein also does not compete, indicating a role for the three terminal residues of the pre nylated peptide in receptor recognition. This receptor may serve to di rect newly prenylated proteins to a microsomal compartment for complet ion of processing prior to trafficking to their final destination in t he cell.