The Biology and Enzymology of ProteinN-Myristoylation

Abstract

N-myristoyltransferase Protein N-myristoylation refers to the covalent attachment of myristate, a 14-carbon saturated fatty acid, to the N-terminal glycine of eukaryotic and viral proteins.N-Myristoylproteins have diverse functions and intracellular destinations. They include proteins involved in a wide variety of signal transduction cascades. In general, N-myristoylation is an irreversible protein modification that occurs co-translationally following removal of the initiator methionine residue by cellular methionylaminopeptidases (1Wolven A. Okamura H. Rosenblatt Y. Resh M.D. Mol. Biol. Cell. 1997; 8: 1159-1173Crossref PubMed Scopus (146) Google Scholar, 2Towler D.A. Adams S.P. Eubanks S.R. Towery D.S. Jackson-Machelski E. Glaser L. Gordon J.I. Proc. Natl. Acad. Sci. U. S. A. 1987; 84: 2708-2712Crossref PubMed Scopus (169) Google Scholar). N-Myristoylation can also occur post-translationally, as in the case of the pro-apoptotic protein BID where proteolytic cleavage by caspase 8 reveals a “hidden” myristoylation motif (3Zha J. Weiler S. Oh K.J. Wei M.C. Korsmeyer S.J. Science. 2000; 290: 1761-1765Crossref PubMed Scopus (471) Google Scholar). N-Myristoylation promotes weak and reversible protein-membrane and protein-protein interactions (4Peitzsch R.M. McLaughlin S. Biochemistry. 1993; 32: 10436-10443Crossref PubMed Scopus (459) Google Scholar, 5Murray D. Ben-Tal N. Honig B. McLaughlin S. Structure. 1997; 5: 985-989Abstract Full Text Full Text PDF PubMed Scopus (198) Google Scholar). Typically, myristate acts in concert with other mechanisms to regulate protein targeting and function. Some proteins (e.g. MARCKS, Src) employ “myristoyl-electrostatic switches” where membrane association is promoted by myristate plus electrostatic interactions between positively charged protein side chains and negatively charged membrane phospholipids (6McLaughlin S. Aderem A. Trends Biochem. Sci. 1995; 20: 272-276Abstract Full Text PDF PubMed Scopus (612) Google Scholar, 7Resh M.D. Biochim. Biophys. Acta. 1999; 1451: 1-16Crossref PubMed Scopus (1066) Google Scholar). In other N-myristoylproteins, ligand binding (Arfs, recoverin (8Goldberg J. Cell. 1998; 95: 237-248Abstract Full Text Full Text PDF PubMed Scopus (431) Google Scholar, 9Ames J.B. Ishima R. Tanaka T. Gordon J.I. Stryer L. Ikura M. Nature. 1997; 389: 198-202Crossref PubMed Scopus (426) Google Scholar)) or proteolytic cleavage (HIV-1 Pr55gag/p17MA (10Hermida-Matsumoto L. Resh M.D. J. Virol. 1999; 73: 1902-1908Crossref PubMed Google Scholar)) produces a conformational change that exposes or sequesters the acyl chain (“myristoyl-conformational switch”). A subset of proteins undergoes post-translational covalent modification with one or more palmitoyl groups after N-myristoylation. Examples of these dually acylated proteins include members of the Src family of tyrosine kinases (Fyn, Lck), α subunits of heterotrimeric G-proteins, endothelial nitric-oxide synthase, and the yeast vacuolar protein Vac8p (11Dunphy J.T. Linder M.E. Biochim. Biophys. Acta. 1998; 1436: 245-261Crossref PubMed Scopus (312) Google Scholar). Cys serves as the acceptor site for palmitate.S-Palmitoylation is reversible, providing a mechanism for regulated interactions between these N-myristoylproteins and cellular membranes and/or other proteins (7Resh M.D. Biochim. Biophys. Acta. 1999; 1451: 1-16Crossref PubMed Scopus (1066) Google Scholar, 12Linder M.E. Tamanoi F. Sigman D.S. The Enzymes: Protein Lipidation. Academic Press, Inc., San Diego, CA2000: 215-240Google Scholar). For example, turnover of the palmitoyl moiety in N-myristoylated Giα subunits is stimulated by activation of the 5-hydroxytryptamine-1a receptor (13Chen C.A. Manning D.R. J. Biol. Chem. 2000; 275: 23516-23522Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar). Depalmitoylation of Giα has no overt effects on membrane association (14Huang C. Duncan J.A. Gilman A.G. Mumby S.M. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 412-417Crossref PubMed Scopus (83) Google Scholar) but may have functional consequences for G-protein de-activation; in vitro studies have shown that S-acylated Giα is resistant to the GTPase-activating protein activity of RGS (regulators of G-protein signaling) proteins (15Tu Y. Wang J. Ross E.M. Science. 1997; 278: 1132-1135Crossref PubMed Scopus (130) Google Scholar). The “kinetic bilayer trapping” hypothesis (16Shahinian S. Silvius J.R. Biochemistry. 1995; 34: 3813-3822Crossref PubMed Scopus (261) Google Scholar) was proposed to explain the operation of this “dual fatty acylation switch.” According to the hypothesis, proteins with myristate are able to transiently interact with membranes. This allows subsequent palmitoylation by plasma membrane-associated palmitoylS-transferase (17Dunphy J.T. Greentree W.K. Manahan C.L. Linder M.E. J. Biol. Chem. 1996; 271: 7154-7159Abstract Full Text Full Text PDF PubMed Scopus (156) Google Scholar) and stable membrane association because of a slower off rate of th