Myristoylation of proteins

Myristoylation is the post-translational addition of the 14-carbon fatty acid myristate to the N-terminal glycine of proteins via an amide link. Myristoylation of proteins helps to anchor them to membranes. 

Maurer-Stroh S, Eisenhaber B, Eisenhaber F. 2002. N-terminal N-myristoylation of proteins Prediction of substrate... 

Myristic acid may be linked via an amide bond to the a-amino group of the N-terminal glycine residue of selected proteins (Figure 9.18). The reaction is referred to as A -myristoylation and is catalyzed by myristoyl—CoAtprolein N-myris-toyltransferase, known simply as NMT. A -Myristoyl-anchored proteins include the catalytic subunit of cAMP-dependent protein kinase, the ppSff tyrosine kinase, the phosphatase known as calcineurin B, the a-subunit of G proteins (involved in GTP-dependent transmembrane signaling events), and the gag proteins of certain retroviruses, including the FHV-l virus that causes AIDS. 

Farazi TA, Waksman G, Gordon JT (2001) The biology and enzymology of protein N-myristoylation. J Biol Chem 276 39501-39504... 

Some proteins can be posttranslationally modified by the addition of prenyl groups. Prenyl groups are long-chain, unsaturated hydrocarbons that are intermediates in isoprenoid synthesis. The farnesyl group has 15 carbons, and the geranylgeranyl has 20 carbons. They are attached to a cysteine residue near the end of the protein as a thiol ether (Protein-S-R). Other proteins can have a long-chain fatty acid (C14=myristoyl, C16=palmitoyl) attached to the amino terminus as an amide. These fatty acid modifications can increase the association of proteins with the membrane. 

Lipidation of proteins may involve N-terminal myristoylation,131 S-prenylation (farnesyl- and geranylgeranyl groups) of cysteine residues at or close to the C-terminus, and S-palmitoylation[31 of cysteines throughout proteins (Scheme 2). 

In particular cases where small amounts of myristoylated peptides are required, enzymatic N-myristoylation of unprotected and purified peptides can be achieved using the yeast TV-myristoyltransferase. This procedure has been applied for N-myristoylation of the N-terminal deca-, dodeca-, and tetradecamer fragment of pp60vsrc, the transforming protein of Rous sarcoma virus. 31 This method is particularly useful when [3H]-labeled myristoylated compounds are required. 

As discussed for N-myristoylation and S-prenylation, even S-acylation of proteins with a fatty acid which in the vast majority of cases is the C16 0 palmitic acid, plays a fundamental role in the cellular signal-transduction process (Table l). 2-5 14 While N-myristoylation and S-prenylation are permanent protein modifications due to the amide- and sulfide-type linkage, the thioester bond between palmitic acid and the peptide chain is rather labile and palmi-toylation is referred to as a dynamic modification. 64 This reversibility plays a crucial role in the modulation of protein functions since the presence or absence of a palmitoyl chain can determine the membrane localization of the protein and can also be used to regulate the interactions of these proteins with other proteins. Furthermore, a unique consensus sequence for protein palmitoylation has not been found, in contrast to the strict consensus sequences required for N-myristoylation and S-prenylation. Palmitoylation can occur at N- or C-terminal parts of the polypeptide chain depending on the protein family and often coexists with other types of lipidation (see Section 6.4.1.4). Given the diversity of protein sequences... 

To mimic nature in its irreversible monolipidation of proteins by N-myristoylation and S-prenylation, peptides are N-acylated with fatty acids or N-alkylated with linear or branched, saturated or unsaturated aliphatic chains as well as by incorporation of newly synthesized lipo-amino acids. 

McNamara RK, Lenox RH Distribution of protein kinase C substrates MARCKS and MRP in the postnatal developing rat brain. J Comp Neurol 397 337-356, 1998 McNamara RK, Stumpo DJ, Morel LM, et al Effects of reduced myristoylated alanine rich C-kinase substrate expression on spatial learning in mutant mice transgenic rescue and interaction with gene background. Proc Natl Acad Sci U S A95 14517-14522, 1998... 

Fig. 3.13. Lipid anchors and basic regions as elements of the membrane association of proteins. Examples for proteins which exhibit basic residues near a lipid anchor, a) Src kinase (see ch. 8) possess a myristoyl anchor at the N-terminus as well as a stretch of basic residues, b) In Ki-Ras proteins (see ch. 9) there is a farnesyl residue at the C-terminus that serves as a lipid anchor, as weU as a stretch of Lys residues. Negatively charged head groups of phospholipids are shown as filled circles. X any amino acid.

Fig. 7.5. Functional domains of protein kinase A. The functional domains of the catalytic (C) and regulatory (R) subunits of protein kinase A (bovine) are shown in a hnear configuration. M myristoylation.

Of the many substrates of protein kinase C, the MARCKS proteins are highhghted as very well characterized and specific substrates of protein kinase C (review Aderem, 1995). The abbreviation MARCKS stands for myristoylated, alanine-rich C-kinase substrate. 

Resh MD. Fatty acylation of proteins new insights into membrane targeting of myristoylated and palmitoylated proteins. Biochim Biophys Acta 1999 1451(1) 1-16. 

G-protein a-subunits also possess specific residues that can be covalently modified by bacterial toxins. Cholera toxin catalyzes the transfer of ADP-ribose moiety of NAD to a specific arginine residue in certain a-subunits, whereas pertussis toxin ADP-ribosylates those a-subunits that contain a specific cysteine residue near the carboxy-terminus. Modification of the a-subunit by cholera toxin persistently activates these protein by inhibiting their GTPase activity, whereas pertussis toxin inactives Gia protein and thereby results in the uncoupling of receptor from the effector. G-protein a-subunits are regulated by covalent modifications by fatty acids myristate and palmate. These lipid modifications serve to anchor the subunits to the membrane and increase the interaction with other protein and also increase the affinity of the a-subunit for 3y. In this regard, the myristoylation of Gia is required for adenylyl cyclase inhibition in cell-free assay (Taussig et al. 1993). 

Fig. 17.4 (A) Inhibition of MCBP by NIP71. (B) Deacylation of protein-myristoyl-CoA complex. For details see Raju et al. (1997).

Duronio, R. J., Reed, S. I., and Gordon, J. I. 1992. Mutations of human myristoyl-CoA protein N-myristoyltransferase cause temperature-sensitive myristic acid auxotrophy in Saccharomyces cerevisiae. Proc. Natl. Acad. Sci. USA 89 4129—4133. 

Harper, D. R., Gilbert, R. L., Blunt, C., and Mcllhinney, R. A. 1993. Inhibition of varicella-zoster virus replication by an inhibitor of protein myristoylation. 1. Gen. Virol. 74 1181-1184. 

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