Protein prenylation reaction

FIGURE 9.19 Proteins containing the C-terminal sequence CAAX can undergo prenylation reactions that place thioether-linked farnesyl or geranylgeranyl groups at the cysteine side chain. Prenylation is accompanied by removal of the AAX peptide and methylation of the carboxyl group of the cysteine residue, which has become the C-terminal residue. 

Protein prenylation (also called isoprenylation) attaches a 15-carbon, farnesyl diphosphate or a 20-carbon geranylgeranyl diphosphate to the cysteine residue near the C termini of the target proteins (Overmeyer et al., 1998 Rodrfguez-Concepcion et al., 1999a). This reaction is conserved both in animals and plants. The functions of the target proteins include signal transduction, nuclear architecture, and vesicular transport. 

Nuclear lamin proteins and the Ras proteins were later shown to be modified by this prenylation reaction [4-6]. The prenyl molecule involved was foimd to be a 15-carbon farnesyl moiety attached to a C-terminal cysteine by a thioether bond [5,6]. Since these farnesylated targets were involved in cell division and signal transduction associated with cell proliferation, the findings suggested an important role for this pathway in tumor cell... 

Prenylation (covalent attachment of an isoprenoid see Fig. 27-30) is a common mechanism by which proteins are anchored to the inner surface of cellular membranes in mammals (see Fig. 11-14). In some of these proteins the attached lipid is the 15-carbon farnesyl group others have the 20-carbon geranylgeranyl group. Different enzymes attach the two types of lipids. It is possible that prenylation reactions target proteins to different membranes, depending on which lipid is attached. Protein prenylation is another important role for the isoprene derivatives of the pathway to cholesterol. 

We confirmed that the Insect Cell Extract has the ability to perform eukaryote-specific protein modifications, such as AT-myristoylation (3) and prenylation (4). To obtain such modified proteins effectively, specific substrates for each protein modification should be added to the translation reaction mixture. 

A third lipid anchor is provided by the polyprenyl farnesyl (15-carbon) and geranylgeranyl (20-carbon) groups in thioether linkage to cysteine residues. These must be present in specific recognition sequences at the C termini of proteins, most often with the sequence CAAX.211-215 The prenylation (also called isoprenyla-tion) reaction is followed by proteolytic removal of the last three residues (AAX) and methylation of the new C-terminal carboxyl group as is discussed in Chapter 11, Section D,3. See also Chapter 22, Section A,4. 

Figure 6.4 De novo synthesis of cholesterol. Pathway of cholesterol biosynthesis. Synthesis begins with the transport of acetyl-CoA from the mitochondrion to the cytosol. The rate-limiting step occurs at the 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase catalysed step. The phosphorylation reactions are required to solubilise the isoprenoid intermediates in the pathway. Intermediates in the pathway are used for the synthesis of prenylated proteins, dolichol, coenzyme Q and the side chain of haem a.

Several papers report new findings on ubiquinone biosynthesis. A mitochondrial membrane-rich preparation from baker s yeast can convert 4-hydroxybenzoate and isopentenyl pyrophosphate into the ubiquinone precursor 3-all-trans-hexaprenyl-4-hydroxybenzoate (234). Details of the cell-free system are presented. With preformed polyprenyl pyrophosphates, the system catalysed the polyprenylation of several aromatic compounds, e.g. methyl 4-hydroxybenzoate, 4-hydroxybenzaldehyde, 4-hydroxybenzyl alcohol, and 4-hydroxycinnamate. No evidence was obtained for the involvement of 4-hydr-oxybenzoyl-CoA or 4-hydroxybenzoyl-S-protein in the reaction. With shorter-chain prenyl pyrophosphates a shorter prenyl side-chain was introduced, e.g. geranyl and farnesyl pyrophosphates gave products with a 3-diprenyl and 3-triprenyl side-chain respectively. A crude enzyme preparation from E. coli... 

Posttranslational modification reactions prepare polypeptides to serve their specific functions and direct them to specific cellular or extracellular locations. Examples of these modifications include proteolytic processing (e.g., removal of signal proteins), glycosylation, methylation, phosphorylation, hydroxylation, lipophilic modifications (e.g., N-myristoylation and prenylation), and disulfide bond formation. 

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