Palmitoylation

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In palmitoylation, a palmitoyl group (derived from palmitic acid, pictured above) is added. Palmitic acid.svg
In palmitoylation, a palmitoyl group (derived from palmitic acid, pictured above) is added.
Palmitoylation of a cysteine residue Palmitoylation.png
Palmitoylation of a cysteine residue
Left Palmitoylation (red) anchors Ankyrin G to the plasma membrane. Right Close up. Palmityl residue in yellow. PalmitoylationAnkGc.jpg
Left Palmitoylation (red) anchors Ankyrin G to the plasma membrane. Right Close up. Palmityl residue in yellow.
Palmitoylation of Gephyrin Controls Receptor Clustering and Plasticity of GABAergic Synapses Gephyrinc.jpg
Palmitoylation of Gephyrin Controls Receptor Clustering and Plasticity of GABAergic Synapses

Palmitoylation is the covalent attachment of fatty acids, such as palmitic acid, to cysteine (S-palmitoylation) and less frequently to serine and threonine (O-palmitoylation) residues of proteins, which are typically membrane proteins. [2] The precise function of palmitoylation depends on the particular protein being considered. Palmitoylation enhances the hydrophobicity of proteins and contributes to their membrane association. Palmitoylation also appears to play a significant role in subcellular trafficking of proteins between membrane compartments, [3] as well as in modulating protein–protein interactions. [4] In contrast to prenylation and myristoylation, palmitoylation is usually reversible (because the bond between palmitic acid and protein is often a thioester bond). The reverse reaction in mammalian cells is catalyzed by acyl-protein thioesterases (APTs) in the cytosol and palmitoyl protein thioesterases in lysosomes. Because palmitoylation is a dynamic, post-translational process, it is believed to be employed by the cell to alter the subcellular localization, protein–protein interactions, or binding capacities of a protein.

Contents

An example of a protein that undergoes palmitoylation is hemagglutinin, a membrane glycoprotein used by influenza to attach to host cell receptors. [5] The palmitoylation cycles of a wide array of enzymes have been characterized in the past few years, including H-Ras, Gsα, the β2-adrenergic receptor, and endothelial nitric oxide synthase (eNOS). In signal transduction via G protein, palmitoylation of the α subunit, prenylation of the γ subunit, and myristoylation is involved in tethering the G protein to the inner surface of the plasma membrane so that the G protein can interact with its receptor. [6]

Mechanism

S-palmitoylation is generally done by proteins with the DHHC domain. Exceptions exist in non-enzymatic reactions. Acyl-protein thioesterase (APT) catalyses the reverse reaction. [7] Other acyl groups such as stearate (C18:0) or oleate (C18:1) are also frequently accepted, more so in plant and viral proteins, making S-acylation a more useful name. [8] [9]

Several structures of the DHHC domain have been determined using X-ray crystallography. It contains a linearly-arranged catalytic triad of Asp153, His154, and Cys156. It runs on a ping-pong mechanism, where the cysteine attacks the acyl-CoA to form an S-acylated DHHC, and then the acyl group is transferred to the substrate. DHHR enzymes exist, and it (as well as some DHHC enzymes) may use a ternary complex mechanism instead. [10]

An inhibitor of S-palmitoylation by DHHC is 2-Bromopalmitate (2-BP). 2-BP is a nonspecific inhibitor that also halts many other lipid-processing enzymes. [7]

The palmitoylome

A meta-analysis of 15 studies produced a compendium of approximately 2,000 mammalian proteins that are palmitoylated. The highest associations of the palmitoylome are with cancers and disorders of the nervous system. Approximately 40% of synaptic proteins were found in the palmitoylome. [11]

Biological function

Substrate presentation

Palmitoylation mediates the affinity of a protein for lipid rafts and facilitates the clustering of proteins. [12] The clustering can increase the proximity of two molecules. Alternatively, clustering can sequester a protein away from a substrate. For example, palmitoylation of phospholipase D (PLD) sequesters the enzyme away from its substrate phosphatidylcholine. When cholesterol levels decrease or PIP2 levels increase the palmitate mediated localization is disrupted, the enzyme trafficks to PIP2 where it encounters its substrate and is active by substrate presentation. [13] [14] [15]

General Anesthesia

Palmitoylation is necessary for the inactivation of anesthesia inducing potassium channels and the localization of GABAAR in synapses. Anesthetics compete with palmitate in ordered lipids and this release gives rise to a component of membrane-mediated anesthesia. For example the anesthesia channel TREK-1 is activated by anesthetic displacement from GM1 lipids. [16] The palmitoylation site is specific for palmitate over prenylation, however, the anesthetics appear to compete non-specifically. This non-selective competition of anesthetic with palmitate likely gives rise to rise to the Myer-Overton correlation.

Synapse formation

Scientists have appreciated the significance of attaching long hydrophobic chains to specific proteins in cell signaling pathways. A good example of its significance is in the clustering of proteins in the synapse. A major mediator of protein clustering in the synapse is the postsynaptic density (95kD) protein PSD-95. When this protein is palmitoylated it is restricted to the membrane. This restriction to the membrane allows it to bind to and cluster ion channels in the postsynaptic membrane. Also, in the presynaptic neuron, palmitoylation of SNAP-25 directs it to partition in the cell membrane [17] and allows the SNARE complex to dissociate during vesicle fusion. This provides a role for palmitoylation in regulating neurotransmitter release. [18]

Palmitoylation of delta catenin seems to coordinate activity-dependent changes in synaptic adhesion molecules, synapse structure, and receptor localizations that are involved in memory formation. [19]

Palmitoylation of gephyrin has been reported to influence GABAergic synapses. [1]

See also

Related Research Articles

<span class="mw-page-title-main">Lipid-anchored protein</span> Membrane protein

Lipid-anchored proteins are proteins located on the surface of the cell membrane that are covalently attached to lipids embedded within the cell membrane. These proteins insert and assume a place in the bilayer structure of the membrane alongside the similar fatty acid tails. The lipid-anchored protein can be located on either side of the cell membrane. Thus, the lipid serves to anchor the protein to the cell membrane. They are a type of proteolipids.

In chemistry, acylation is a broad class of chemical reactions in which an acyl group is added to a substrate. The compound providing the acyl group is called the acylating agent. The substrate to be acylated and the product include the following:

<span class="mw-page-title-main">Theories of general anaesthetic action</span> How drugs induce reversible suppression of consciousness

A general anaesthetic is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist/anesthesiologist to induce or maintain general anaesthesia to facilitate surgery.

<span class="mw-page-title-main">Myristoylation</span>

Myristoylation is a lipidation modification where a myristoyl group, derived from myristic acid, is covalently attached by an amide bond to the alpha-amino group of an N-terminal glycine residue. Myristic acid is a 14-carbon saturated fatty acid (14:0) with the systematic name of n-tetradecanoic acid. This modification can be added either co-translationally or post-translationally. N-myristoyltransferase (NMT) catalyzes the myristic acid addition reaction in the cytoplasm of cells. This lipidation event is the most common type of fatty acylation and is present in many organisms, including animals, plants, fungi, protozoans and viruses. Myristoylation allows for weak protein–protein and protein–lipid interactions and plays an essential role in membrane targeting, protein–protein interactions and functions widely in a variety of signal transduction pathways.

<span class="mw-page-title-main">ACOT2</span> Protein-coding gene in the species Homo sapiens

Acyl-CoA thioesterase 2, also known as ACOT2, is an enzyme which in humans is encoded by the ACOT2 gene.

<span class="mw-page-title-main">ACOT4</span> Protein-coding gene in the species Homo sapiens

Acyl-coenzyme A thioesterase 4 is an enzyme that in humans is encoded by the ACOT4 gene.

<span class="mw-page-title-main">ACOT11</span> Protein-coding gene in the species Homo sapiens

Acyl-coenzyme A thioesterase 11 also known as StAR-related lipid transfer protein 14 (STARD14) is an enzyme that in humans is encoded by the ACOT11 gene. This gene encodes a protein with acyl-CoA thioesterase activity towards medium (C12) and long-chain (C18) fatty acyl-CoA substrates which relies on its StAR-related lipid transfer domain. Expression of a similar murine protein in brown adipose tissue is induced by cold exposure and repressed by warmth. Expression of the mouse protein has been associated with obesity, with higher expression found in obesity-resistant mice compared with obesity-prone mice. Alternative splicing results in two transcript variants encoding different isoforms.

<span class="mw-page-title-main">DHHC domain</span>

In molecular biology the DHHC domain is a protein domain that acts as an enzyme, which adds a palmitoyl chemical group to proteins in order to anchor them to cell membranes. The DHHC domain was discovered in 1999 and named after a conserved sequence motif found in its protein sequence. Roth and colleagues showed that the yeast Akr1p protein could palmitoylate Yck2p in vitro and inferred that the DHHC domain defined a large family of palmitoyltransferases. In mammals twenty three members of this family have been identified and their substrate specificities investigated. Some members of the family such as ZDHHC3 and ZDHHC7 enhance palmitoylation of proteins such as PSD-95, SNAP-25, GAP43, Gαs. Others such as ZDHHC9 showed specificity only toward the H-Ras protein. However, a recent study questions the involvement of classical enzyme-substrate recognition and specificity in the palmitoylation reaction. Several members of the family have been implicated in human diseases.

<span class="mw-page-title-main">ACOT6</span> Protein-coding gene in the species Homo sapiens

Acyl-CoA thioesterase 6 is a protein that in humans is encoded by the ACOT6 gene. The protein, also known as C14orf42, is an enzyme with thioesterase activity.

Palmitoyl acyltransferase is a group of enzymes that transfer palmityl group to -SH group on cysteine on a protein. This modification increases the hydrophobicity of the protein, thereby increasing the association to plasma membrane or other intramembraneous compartments.

<span class="mw-page-title-main">Acyl-CoA thioesterase 9</span> Protein-coding gene in humans

Acyl-CoA thioesterase 9 is a protein that is encoded by the human ACOT9 gene. It is a member of the acyl-CoA thioesterase superfamily, which is a group of enzymes that hydrolyze Coenzyme A esters. There is no known function, however it has been shown to act as a long-chain thioesterase at low concentrations, and a short-chain thioesterase at high concentrations.

<span class="mw-page-title-main">ACOT13</span> Protein-coding gene in the species Homo sapiens

Acyl-CoA thioesterase 13 is a protein that in humans is encoded by the ACOT13 gene. This gene encodes a member of the thioesterase superfamily. In humans, the protein co-localizes with microtubules and is essential for sustained cell proliferation.

<span class="mw-page-title-main">ACOT1</span> Protein-coding gene in the species Homo sapiens

Acyl-CoA thioesterase 1 is a protein that in humans is encoded by the ACOT1 gene.

<span class="mw-page-title-main">Acyl-protein thioesterase</span> Enzymes that cleave off lipid modifications on proteins

Acyl-protein thioesterases are enzymes that cleave off lipid modifications on proteins, located on the sulfur atom of cysteine residues linked via a thioester bond. Acyl-protein thioesterases are part of the α/β hydrolase superfamily of proteins and have a conserved catalytic triad. For that reason, acyl-protein thioesterases are also able to hydrolyze oxygen-linked ester bonds.

A proteolipid is a protein covalently linked to lipid molecules, which can be fatty acids, isoprenoids or sterols. The process of such a linkage is known as protein lipidation, and falls into the wider category of acylation and post-translational modification. Proteolipids are abundant in brain tissue, and are also present in many other animal and plant tissues. They include ghrelin, a peptide hormone associated with feeding. Many proteolipids are composed of proteins covalenently bound to fatty acid chains, often granting them an interface for interacting with biological membranes. They are not to be confused with lipoproteins, a kind of spherical assembly made up of many molecules of lipids and some apolipoproteins.

Substrate presentation is a biological process that activates a protein. The protein is sequestered away from its substrate and then activated by release and exposure of the protein to its substrate. A substrate is typically the substance on which an enzyme acts but can also be a protein surface to which a ligand binds. The substrate is the material acted upon. In the case of an interaction with an enzyme, the protein or organic substrate typically changes chemical form. Substrate presentation differs from allosteric regulation in that the enzyme need not change its conformation to begin catalysis. Substrate presentation is best described for nanoscopic distances (<100 nm).

Palmitate mediated localization is a biological process that trafficks a palmitoylated protein to ordered lipid domains.

<span class="mw-page-title-main">Cholesterol signaling</span>

Cholesterol is a cell signaling molecule that is highly regulated in eukaryotic cell membranes. In human health, its effects are most notable in inflammation, metabolic syndrome, and neurodegeneration. At the molecular level, cholesterol primarily signals by regulating clustering of saturated lipids and proteins that depend on clustering for their regulation.

PIP2 domains are a type of cholesterol-independent lipid domain formed from phosphatidylinositol and positively charged proteins in the plasma membrane. They tend to inhibit GM1 lipid raft function.

Membrane-mediated anesthesia or anaesthesia (UK) is a mechanism of action that involves an anesthetic exerting its effects through the lipid membrane. Established mechanism exists for both general and local anesthetics. The anesthetic binding site is within ordered lipids and binding disrupts the function of the ordered lipid. See Theories of general anaesthetic action for a broader discussion of purely theoretical mechanisms.

References

  1. 1 2 Dejanovic B, Semtner M, Ebert S, Lamkemeyer T, Neuser F, Lüscher B, Meier JC, Schwarz G (July 2014). "Palmitoylation of gephyrin controls receptor clustering and plasticity of GABAergic synapses". PLOS Biology. 12 (7): e1001908. doi: 10.1371/journal.pbio.1001908 . PMC   4099074 . PMID   25025157.
  2. ↑ Linder, M.E., "Reversible modification of proteins with thioester-linked fatty acids," Protein Lipidation, F. Tamanoi and D.S. Sigman, eds., pp. 215-40 (San Diego, CA: Academic Press, 2000).
  3. ↑ Rocks O, Peyker A, Kahms M, Verveer PJ, Koerner C, Lumbierres M, Kuhlmann J, Waldmann H, Wittinghofer A, Bastiaens PI (2005). "An acylation cycle regulates localization and activity of palmitoylated Ras isoforms". Science. 307 (5716): 1746–1752. Bibcode:2005Sci...307.1746R. doi:10.1126/science.1105654. PMID   15705808. S2CID   12408991.
  4. ↑ Basu, J., "Protein palmitoylation and dynamic modulation of protein function," Current Science, Vol. 87, No. 2, pp. 212-17 (25 July 2004), http://www.ias.ac.in/currsci/jul252004/contents.htm
  5. ↑ Palese, Peter; García-Sastre, Adolfo (1999). "INFLUENZA VIRUSES (ORTHOMYXOVIRIDAE) | Molecular Biology". Encyclopedia of Virology. pp. 830–836. doi:10.1006/rwvi.1999.0157. ISBN   9780122270307. Archived from the original on 2012-09-12.
  6. ↑ Wall, MA; Coleman, DE; Lee, E; Iñiguez-Lluhi, JA; Posner, BA; Gilman, AG; Sprang, SR (Dec 15, 1995). "The structure of the G protein heterotrimer Gi alpha 1 beta 1 gamma 2". Cell. 83 (6): 1047–58. doi: 10.1016/0092-8674(95)90220-1 . PMID   8521505.
  7. 1 2 Lanyon-Hogg, T., Faronato, M., Serwa, R. A., & Tate, E. W. (2017). Dynamic Protein Acylation: New Substrates, Mechanisms, and Drug Targets. Trends in Biochemical Sciences, 42(7), 566–581. doi:10.1016/j.tibs.2017.04.004
  8. ↑ Li, Y; Qi, B (2017). "Progress toward Understanding Protein S-acylation: Prospective in Plants". Frontiers in Plant Science. 8: 346. doi: 10.3389/fpls.2017.00346 . PMC   5364179 . PMID   28392791.
  9. ↑ "Proteolipids - proteins modified by covalent attachment to lipids - N-myristoylated, S-palmitoylated, prenylated proteins, ghrelin, hedgehog proteins". www.lipidmaps.org.co.uk. Retrieved 19 July 2021.
  10. ↑ Rana, MS; Lee, CJ; Banerjee, A (28 February 2019). "The molecular mechanism of DHHC protein acyltransferases". Biochemical Society Transactions. 47 (1): 157–167. doi:10.1042/BST20180429. PMID   30559274. S2CID   56175691.
  11. ↑ Sanders SS, Martin DD, Butland SL, Lavallée-Adam M, Calzolari D, Kay C, Yates JR, Hayden MR (August 2015). "Curation of the Mammalian Palmitoylome Indicates a Pivotal Role for Palmitoylation in Diseases and Disorders of the Nervous System and Cancers". PLOS Computational Biology. 11 (8): e1004405. Bibcode:2015PLSCB..11E4405S. doi: 10.1371/journal.pcbi.1004405 . PMC   4537140 . PMID   26275289.
  12. ↑ Levental, I.; Lingwood, D.; Grzybek, M.; Coskun, U.; Simons, K. (3 December 2010). "Palmitoylation regulates raft affinity for the majority of integral raft proteins". Proceedings of the National Academy of Sciences. 107 (51): 22050–22054. Bibcode:2010PNAS..10722050L. doi: 10.1073/pnas.1016184107 . PMC   3009825 . PMID   21131568.
  13. ↑ Petersen, EN; Chung, HW; Nayebosadri, A; Hansen, SB (15 December 2016). "Kinetic disruption of lipid rafts is a mechanosensor for phospholipase D." Nature Communications. 7: 13873. Bibcode:2016NatCo...713873P. doi:10.1038/ncomms13873. PMC   5171650 . PMID   27976674.
  14. ↑ Robinson, CV; Rohacs, T; Hansen, SB (September 2019). "Tools for Understanding Nanoscale Lipid Regulation of Ion Channels". Trends in Biochemical Sciences. 44 (9): 795–806. doi:10.1016/j.tibs.2019.04.001. PMC   6729126 . PMID   31060927.
  15. ↑ Petersen, EN; Pavel, MA; Wang, H; Hansen, SB (28 October 2019). "Disruption of palmitate-mediated localization; a shared pathway of force and anesthetic activation of TREK-1 channels". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1862 (1): 183091. doi:10.1016/j.bbamem.2019.183091. PMC   6907892 . PMID   31672538.
  16. ↑ Pavel, Mahmud Arif; Petersen, E. Nicholas; Wang, Hao; Lerner, Richard A.; Hansen, Scott B. (16 June 2020). "Studies on the mechanism of general anesthesia". Proceedings of the National Academy of Sciences. 117 (24): 13757–13766. doi: 10.1073/pnas.2004259117 . PMC   7306821 .
  17. ↑ Greaves, Jennifer (March 2011). "Differential palmitoylation regulates intracellular patterning of SNAP25". Journal of Cell Science. 124 (8): 1351–1360. doi:10.1242/jcs.079095. PMC   3065388 . PMID   21429935.
  18. ↑ "Molecular Mechanisms of Synaptogenesis." Edited by Alexander Dityatev and Alaa El-Husseini. Springer: New York, NY. 2006. pg. 72-75
  19. ↑ Brigidi GS, Sun Y, Beccano-Kelly D, Pitman K, Jobasser M, Borgland SL, Milnerwood AJ, Bamji SX (January 23, 2014). "Palmitoylation of [delta]-catenin by DHHC5 mediates activity-induced synapse plasticity". Nature Neuroscience. 17 (4): 522–532. doi:10.1038/nn.3657. PMC   5025286 . PMID   24562000.

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