thumb|"prenyl-" the functional groupprenylation, or isoprenylation, or lipidation is the addition of hydrophobic molecules to a protein or chemical compound. it is usually assumed that prenyl groups (3-methyl-but-2-en-1-yl) facilitate attachment to cell membranes, similar to lipid anchor like the gpi anchor, though direct evidence is missing. prenyl groups have been shown to be important for protein-protein binding through specialized prenyl-binding domains. == protein prenylation == protein prenylation involves the transfer of either a farnesyl or a geranyl-geranyl moiety to c-terminal cysteine(s) of the target protein. there are three enzymes that carry out prenylation in the cell, farnesyl transferase, caax protease and geranylgeranyl transferase i. pdf farnesylation is a type of prenylation, a post-translational modification of proteins by which an isoprenyl group is added to a cysteine residue. it is an important process to mediate protein-protein interactions and protein-membrane interactions. === farnesyltransferase and geranylgeranyltransferase i === farnesyltransferase and geranylgeranyltransferase i are very similar proteins. they consist of two subunits, the Î±-subunit, which is common to both enzymes, and the Î²-subunit, whose sequence identity is just 25%. these enzymes recognise the caax box at the c-terminus of the target protein. c is the cysteine that is prenylated, a is any aliphatic amino acid, and the identity of x determines which enzyme acts on the protein. farnesyltransferase recognizes caax boxes where x = m, s, q, a, or c, whereas geranylgeranyltransferase i recognizes caax boxes with x = l or e. === rab geranylgeranyl transferase === rab geranylgeranyltransferase, or geranylgeranyl transferase ii, transfers (usually) two geranylgeranyl groups to the cysteine(s) at the c-terminus of rab proteins. the c-terminus of rab proteins varies in length and sequence and is referred to as hypervariable. thus rab proteins do not have a consensus sequence, such as the caax box, which the rab geranylgeranyl transferase can recognize. 
Membrane_biology Peripheral_membrane_proteins Posttranslational_modification