Isoprenylated proteins

Scheme 15. Kinetic trapping model for the enrichment of isoprenylated proteins with a free acylation site in specific membranes...

The weight of evidence supports the conclusion that the more expressed inhibition of HMG-CoA reductase by a higher statin blood level reduces the concentrations of other essential products, primarily of isoprenylated proteins and possibly ubiquinone, synthetized downstream from mevalonic acid within the peripheral cells. In parallel, it was also recognized that statins exert pleiotropic effects in various cells far beyond the originally described inhibition of hepatic cholesterol synthesis. All of these effects are considered to be class-specific for the statins. It is important to emphasize that the frequency of untoward side effects observed with the various statins can be related to their potency, the number of metabolic inter-... 

Kohl, N.E., Diehl, R.E., Schaber, M.D., Rands, E., Soderman, D.D., He, B., Moores, S.L., Pomphano, D.L., Ferro-Novick, S., Powers, S., et al. (1991). Structural homology among mammalian and saccharomyces cerevisiae isoprenyl-protein transferases. J Biol Chem 266 18884-18888. 

Ma, Y.T., Shi, Y.Q., Lim, Y.H., McGrail, S.H., Ware, J.A., and Rando, R.R. (1994). Mechanistic studies on human platelet isoprenylated protein methyltransferase farnesyl-cysteine analogs block platelet aggregation without inhibiting the methyltransferase. Biochemistry 33 5414-5420. 

Kohl, N.E., et al. (1991). Structural homology amoug manuualiau aud Saccharomyces cerevisiae isoprenyl-protein transferases. J Biol Chem 266 18884-18888. 

Gilbert, B.A.,Tan,E.W., Perez-Sala, D.,andRando, R.R. (1992). Structure activity studies on the retinal rod outer segment isoprenylated protein methyltransferase. J Am Chem Soc 114 3966-3973. 

Hrycyna, C.A., and Qarke, S. (1992). Maturation of isoprenylated proteins in Saccharomyces cerevisiae. J Biol Chem 267 10457—10464. 

Danesi, R., McLellan, C.A., and Myers, C.E. (1995). Specific labeling of isoprenylated proteins apphcation to study inhibitors of the post-translational farnesylation and ger-anylgeranylation. Biochem Biophys Res Commun 206 637-643. 

Maltese, W. A. Sheridan, K. M. (1987). Isoprenylated proteins in cultured cells subcellular distribution and changes related to altered morphology and growth arrest induced by mevalonate deprivation. J. Cell Physiol. 133,471-481. 

PPCs Prenylation is the post-translational addition of 15- or 20-carbon isoprenyl lipids to the C-terminus of proteins. Prenylation is an irreverable modification that anchors proteins to the membrane fraction of cells. 

GDP-dissociation inhibitors Bind isoprenylated Rab proteins in the GDP-bound form, resulting in a cytoplasmic complex. 

G protein y subunits are modified on their C-terminal cysteine residues by isoprenylation [26,27]. There is now strong evidence that this modification plays a key role in anchoring the ysubunit and its associated P subunit to the plasmalemma. The importance of this anchoring is illustrated in Figure 19-2, which shows that the ability of py subunits to direct GRKs to ligand-bound receptors depends on this membrane localization. 

Rab is a family of small G proteins involved in membrane vesicle trafficking. Mammalian tissues contain around 30 forms of Rab, which specifically associate with the various types of membrane vesicles and organelles that exist in cells [30,31]. Rab proteins, named originally as ras-related proteins in brain, are isoprenylated and associate with membranes, as do isoprenylated Ras and G protein y subunits. However, unlike these other G proteins, the GTP and GDP binding to Rab appears to regulate its association with membrane compartments. 

There are multiple isoforms of the a and p subunits of soluble GC that exhibit distinct tissue and cellular distributions. Most of the isoforms are expressed in brain, including 0Ci 3 and and P3. The p2 subunit is found primarily in lung. This isoform also contains a consensus sequence at its carboxy terminus for isoprenylation or carboxymethyl-ation, which could serve to anchor the protein to the plasma membrane. It has been proposed that specific isoforms of the a and P subunits of GC may form heterodimers with distinct functional and regulatory properties, although this remains to be established with certainty. 

A first approach to study the interaction of posttranslational modified Ras proteins with membranes was the analysis of binding and exchange of isoprenyl-ated peptides with and between lipid vesicles utilizing a fluorescent bimanyl label. Studies with K-Ras peptides revealed that a single isoprenyl group is sufficient for membrane association only if supported by carboxymethylation of the C-terminal cysteine [227,228]. 

Thus, lipoproteins could be injected over the surface of a lipid covered SPR sensor in a detergent free buffer solution and showed spontaneous insertion into the artificial membrane.171 Again two hydro-phobic modifications are necessary for stable insertion into the lipid layer, whereas lipoproteins with a farnesyl group only dissociate significantly faster out of the membrane. Therefore the isoprenylation of a protein is sufficient to allow interaction with membraneous structures, while trapping of the molecule at a particular location requires a second hydrophobic anchor. Interaction between the Ras protein and its effector Raf-kinase depends on complex formation of Ras with GTP (instead of the Ras GDP complex, present in the resting cell). If a synthetically modified Ras protein with a palmi-... 

The powerful tool of molecular genetics allows the modification of each single amino add in the peptide chain of a protein, e.g. ddetion of side residues necessary for isoprenylation or palmitoylation1361 or introduction of additional charged amino acids for electrostatic interaction with the plasma membrane.1371 Even some artificial modifications can be introduced by means of recombinant enzymes as shown above. 

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. 

Gerber E, Hemmerlin A, Hartmann M, Heintz D, Hartmann MA, Mutterer J, Rodriguez-Concepcion M, Boronat A, Van Dorsselaer A, Rohmer M, CroweU DN, Bach TJ (2009) The plastidial 2-C-methyl-D-erythritol 4-phosphate pathway provides the isoprenyl moiety for protein geranylgeranylation in tobacco BY-2 ceUs. Plant Cell 21 285-300... 

Na MK, Jang JP, Njamen D, Mbafor JT, Fomum ZT, Kim BY, Oh WK, Ahn JS. (2006) Protein tyrosine phosphatase-IB inhibitory activity of isoprenylated flavonoids isolated from Erythrina mildbraedii. J Nat Prod 69 1572-1576. 

Isoprene chains are sometimes used as lipid anchors to fix molecules to membranes (see p. 214). Chlorophyll has a phytyl residue (1 = 4) as a lipid anchor. Coenzymes with isoprenoid anchors of various lengths include ubiquinone (coenzyme Q 1 = 6-10), plastoqui-none (1 = 9), and menaquinone (vitamin K 1 = 4-6). Proteins can also be anchored to membranes by isoprenylation. 

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