Myristoylation

N-myristoyltransferase

Myristoyl-CoA: protein N-myristoyltransferase (NMT, EC 2.3.1.97), the enzyme catalyzing this stable acylation, has been identified in many organisms.

In mammals, two distinct NMT genes referred to as type 1 and 2 have been described. (R3)

NMT1

Human NMT1 appears to be targeted predominately to subcellular fractions enriched in ribosomes, consistent with its role as a co-translational protein modifier (R8)

NMT2

Protein Myristoylation

N-myristoylation is a process involving the covalent attachment of myristate, a 14-carbon saturated fatty acid, to the N-terminal glycine residue of protein. The N-myristoylation process is catalyzed by N-myristoyltransferase (NMT), which is a member of the Gcn5-related N-acetyltransferase (GNAT) superfamily.

In contrast to palmitoylation, myristoylation is irreversible and can occur co- and post-translationally.

Cotranslational myristoylation occurs when an initiator methionine residue is removed by methionine aminopeptidase, followed by the attachment of NMT-regulated myristate. … The half-life of a myristoylated protein bound to membrane is in the order of minutes, in contrast to hours for palmitoylated or double (myristoylated and palmitoylated) modified protein (R10)

The first N-myris­toylproteins were described in 1982. Since that time, a large number of cellular N-myristoylproteins have been identified. These proteins have diverse functions and include serine/threonine kinases , tyrosine kinases, kinase substrates, phosphoprotein phosphatases, other types of proteins involved in signal transduction cascades (e.g. the a subunits of heterotrimeric G prot eins, the constitutively expressed endothelial nitric oxide synthase), and mediators of protein and vesicular transport (e.g. ADP ribosylation factors) (reviewed in R7).

Myristoylation and calcium

In a calcium-free environment, the myristoyl group is sequestered in a hydrophobic pocket where calcium-binding induces a conformational change within recoverin and releases myristate for membrane binding (R10)

Sirtuins may be more efficient in removing long-chain FA

More importantly, this study shows that Sirtuin (Sirt) 2 can remove the myristoyl group from lysine residue on ARF6 suggesting a complex network of NMT/Sirt2-ARF6 regulatory network in GTPase cycle (Kosciuk et al., 2020).

Sirtuin belongs to the family of seven NAD-dependent deacetylases that remove the acetyl group from acetylated histone. However, it was reported in in vitro assays that deacetylase activity in certain members of the Sirt family is weak, and they are more catalytically efficient toward long-chain peptide substrate (myristoylated) compared with acetylated peptide substrate. … The physiology significance of Sirt deacylase activity started after the discovery of its involvement in demyristoylating a lysine residue in TNF-α maturation and extracellular secretion. Sirt 6 is shown to hydrolyze the myristoyl group of both lysine 19 (K19) and 20 (K20), which helps in matured TNF-α secretion (R10)

Desaturases

FADS2 (Δ6-desaturase)

Several years ago, the fact that myristic acid has a specific and dose-dependent increasing effect on Δ6-desaturase (FADS2) activity in cultured rat hepatocytes, whatever the substrate used to measure this enzyme activity (oleic acid, linoleic or α-linolenic acid, Fig. 5), was demonstrated.

No effect was observed on FADS2 mRNA level (Rioux, V., unpublished data). In the same experimental conditions, lauric acid and palmitic acid did not have a similar increasing effect. (R3)

Myristic acid activates Δ6-desaturase activity in cellular models and regulates the PUFA bioavailability in vivo.

However, bioinformatic predictions indicated and biological experiments confirmed that FADS2 is not myristoylated. (R3)

Effect on PUFA

When myristic acid was supplied for 2 months in the diet of rats (from 0.2% to 1.2% of dietary energy), with a constant level of α-linolenic acid in each diet (0.3% of energy), a dose–response accumulation of EPA was exhibited in the liver and plasma (R3).

in humans, compared with a diet containing 0.6% of myristic acid, a diet containing 1.2% of myristic acid for a 5 week consumption period significantly enhanced EPA and DHA levels in the plasma phospholipids and DHA level in the plasma cholesteryl esters.

All these results suggest that the overall conversion of the ω3 precursor to derivatives increases because of the presence of myristic acid in the diet. (R3)

genetic variation in the FADS1/FADS2 cluster can influence not only the PUFA composition of blood lipids but also that of the mother’s milk during lactation. For example, in the rs174553 genotype for this cluster, homozygotes GG have not only significantly less C14:0 but also less C20:4 n-6 (ARA), C20:5 n-3 (EPA), and C22:5 n-3 (DPA) and more C18:1 n-7 than homozygotes AA. (R3)

DES1 and DES2

DES1 catalyzes the last step of de novo ceramide biosynthesis which consists in the introduction of a trans Δ4-double bond in the carbon chain of the dihydroceramide. DES2 possess a bifunctional Δ4-desaturase/C4-hydroxylase activity (R3)

We showed that both DES1 and DES2 are myristoylated and that this N-terminal modification significantly increased the activity of the recombinant DES1 in COS-7 cells. Compared to the same protein level of a recombinant unmyristoylable mutant form of DES1 (N-terminal glycine replaced by an alanine), the desaturase activity of the myristoylable wild-type DES1 was indeed two times higher, in the presence of myristic acid incubated with the cells (R3)

eNOS

Src

Fyn

Lck

G-protein alpha-subinit, at1

Actin

Subsequent studies have revealed that actin, gelsolin, and caspase-activated p21-activated protein kinase 2 are also posttranslationally myristoylated (R8)

Gelsolin

caspase-activated p21-activated protein kinase 2

Special cases

GSK3b

The study below found that an artificially created myristoylated peptide activates GSK3b, while non-myristoylated peptide has less effect on the enzyme. Which means, myristoylation of some endogenous protein may be important for a strong activation of GSK3b.

Notably, both GSK-3α and -3β were highly activated by ZIP (and SCR-ZIP) compared to other protein kinases. In contrast, non-myristoylated ZIP and non-myristoylated SCR-ZIP had less effect on kinase activities (Fig. 1b), suggesting that myristoylation may enhance the off-target effects induced by ZIP.

This suggests that the amphiphilic structure of ZIP, which consists of a hydrophilic charged peptide and a myristoyl group, is important in the modulation of several kinases, including the original target, PKCζ.

The activities of both GSK-3α and -3β were enhanced several-fold in a concentration-dependent manner. (R9)