Proteolipid

A proteolipid is a protein covalently linked to lipid molecules, which can be fatty acids 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 are proteins covalenently bound to fatty acid chains,[1] often granting them an interface for interacting with biological membranes.[2] They are not to be confused with lipoproteins, a kind of spherical assembly made up of many molecules of lipids and some apolipoproteins.

Not to be confused with Lipoprotein.

Depending on the type of fatty acid attached to the protein, a proteolipid can often contain myristoyl, palmitoyl, or prenyl groups. These groups each serve different functions and have different preferences as to which amino acid residue they attach to. The processes are respectively named myristoylation (usually at N-terminal Gly), palmitoylation (to cysteine), and prenylation (also to cysteine). Despite the seemingly specific names, N-myristoylation and S-palmitoylation can also involve some other fatty acids, most commonly in plants and viral proteolipids.[2][3] The article on lipid-anchored proteins has more information on these canonical classes.

There exist some rarer forms of protein acylation that may not have a membrane-related function. They include serine O-octanoylation in ghrelin, serine O-palmitoleoylation in Wnt proteins, and O-palmitoylation in histone H4 with LPCAT1. Hedgehog proteins are double-modified by (N-) palmitate and cholesterol. Some skin ceramides are proteolipids.[2] The amino group on lysine can also be myristoylation via a poorly-understood mechanism.[4]

In bacteria

All bacteria use proteolipids, sometimes confusingly referred to as bacterial lipoproteins, in their cell membrane. A common modification consists of N-acyl- and S‑diacylglycerol attached to an N-terminal cystine residue. Braun's lipoprotein, found in gram-negative bacteria, is a representative of this group. In addition, Mycobacterium O-mycolate proteins destinated for the outer membrane.[5] The plant chloroplast is capable of many of the same modifications that bacteria perform to proteolipids.[6] One database for such N-Acyl Diacyl Glycerylated cell wall proteolipids is DOLOP.[7]

Pathogenic spirochetes, including B. burgdorferi and T. pallidum, use their proteolipid adhesins to stick to victim cells.[8] These proteins are also potent antigens, and are in fact the main immunogens of these two species.[9]

Products of nonribosomal peptide synthase may also involve a peptide structure linked to lipids. These are usually referred to as "lipopeptides".[5]

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See also

References
  1. "MeSH Browser". meshb.nlm.nih.gov. Retrieved 11 March 2018.
  2. "Proteolipids - proteins modified by covalent attachment to lipids - N-myristoylated, S-palmitoylated, prenylated proteins, ghrelin, hedgehog proteins". The LipidWeb. Retrieved 18 July 2019.
  3. 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.
  4. Thomas Lanyon-Hogg, Monica Faronato, Remigiusz A. Serwa, Edward W. Tate (June 1, 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. hdl:10044/1/48121. PMID 28602500.CS1 maint: uses authors parameter (link)
  5. "Microbial Proteolipids and Lipopeptides - glycopeptidolipids, surfactin, iturnins, polymyxins, daptomycin". The LipidWeb. Retrieved 21 July 2019.
  6. Glenz, K; Bouchon, B; Stehle, T; Wallich, R; Simon, MM; Warzecha, H (January 2006). "Production of a recombinant bacterial lipoprotein in higher plant chloroplasts". Nature Biotechnology. 24 (1): 76–7. doi:10.1038/nbt1170. PMID 16327810.
  7. "DOLOP - A Database of Bacterial Lipoproteins". cam.ac.uk. Retrieved 2 January 2017.
  8. Chan, K; Nasereddin, T; Alter, L; Centurion-Lara, A; Giacani, L; Parveen, N (10 May 2016). "Treponema pallidum Lipoprotein TP0435 Expressed in Borrelia burgdorferi Produces Multiple Surface/Periplasmic Isoforms and mediates Adherence". Scientific Reports. 6: 25593. Bibcode:2016NatSR...625593C. doi:10.1038/srep25593. PMC 4861935. PMID 27161310.
  9. Porcella, Stephen F.; Schwan, Tom G. (15 March 2001). "Borrelia burgdorferi and Treponema pallidum: a comparison of functional genomics, environmental adaptations, and pathogenic mechanisms". Journal of Clinical Investigation. 107 (6): 651–656. doi:10.1172/JCI12484. PMC 208952. PMID 11254661.
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