Myristic acid is attached to the transforming protein of Rous sarcoma virus during or immediately after synthesis and is present in both soluble and membrane-bound forms of the protein.

Abstract

Myristic acid, a minor component of cellular fatty acids, has been shown previously to be covalently bound to most molecules of p60, the transforming protein of Rous sarcoma virus. We have now determined at what time during the life cycle of p6Osrc, and where within the cell, this lipid becomes attached to the protein. p6Osrc was found to acquire myristic acid at only one time, during or immediately after its synthesis. p6OSc is known to be synthesized on free polysomes and appears at the cytoplasmic face of the plasma membrane after a lag of 10 min. The addition of myristic acid to p6ps therefore precedes the binding of the protein to the plasma membrane. The lipid attached to p60sr is a permanent, metabolically stable part of the protein; we found no evidence for turnover of the myristyl moiety. However, we did find myristate attached to various soluble forms of p60src and to a large number of cytosolic cellular proteins as well. This demonstrates that the attachment of myristic acid to a protein is not in itself sufficient to convert a soluble protein into a membrane-bound protein.p6 src, the transforming protein of Rous sarcoma virus (RSV) (5) is a protein kinase which phosphorylates tyrosine residues in substrate proteins (7,16,22). p60src undergoes an unusual form of protein modification: the 14-carbon saturated fatty acid, myristic acid, is covalently attached to its amino terminus (39; J. E. Buss and B. M. Sefton, J. Virol., in press). In these studies we have characterized the time and intracellular location of myristic acid addition to p6OSrc and analyzed the effect of temperature-sensitive mutations on this process.Although few studies have examined the biochemistry of fatty acylation of proteins, two different types of modification are known to occur. The 16-carbon saturated fatty acid, palmitic acid, has been shown to be present in a variety of membrane-associated proteins. These include the transferrin receptor (24); p2lras, the transforming protein of Harvey murine sarcoma virus (39); and the El and E2 glycoproteins of Sindbis virus and the G glycoprotein of vesicular stomatitis virus (31, 32). The palmityl group is attached to these proteins via ester bonds to cysteine (30) or possibly serine residues (32). The addition of ester-linked palmitate is clearly a posttranslational event. The fatty acid is added to viral glycoproteins in the Golgi apparatus ca. 20 min after their synthesis (33), and only the mature forms of p2lras and the transferrin receptor contain palmitic acid (25, 39).Only five identified proteins are known to contain a covalently attached myristic acid. These are the cellular and viral forms of p6Osrc (Buss and Sefton, in press), the catalytic subunit of the cyclic AMP-dependent protein kinase (6), the protein phosphatase, calcineurin B (1), the T-cell-specific p56 protein from LSTRA cells (41), and proteins which contain the p15rag protein of mammalian retroviruses (15,35). This last group includes the unglycosylated forms of a number of gag-onc fusion proteins such as Abelson m...

Reconstitution of the Rous sarcoma virus transforming protein pp60v-src into phospholipid vesicles.

“…Covalent acylation of the pp6Ov-src amino terminus with myristic acid has been shown to be necessary, but not sufficient, for localization of pp6Ov-src to cell membranes (9,18,30). Nonmyristylated pp6Ov-src molecules exhibit wild-type tyrosine kinase activity, but are predominantly cytoplasmic and do not transform cells.…”

“…If this association occurred directly through hydrophobic interactions between myristate and membrane lipid fatty acid side chains, one might predict that myristylation of pp6Ov-src would be sufficient for membrane association in vivo. However, experiments performed with t Dedicated to the memory of Bernard L. Resh. various src deletion or temperature-sensitive mutants (9,18) have revealed that not all myristylated pp60-vrc proteins are membrane bound. Wild-type RSV-infected cells also contain small quantities of soluble pp60vsrc molecules, both in monomeric and pp50/pp9O complexed form, which are myristylated but not membrane bound (9).…”

“…However, experiments performed with t Dedicated to the memory of Bernard L. Resh. various src deletion or temperature-sensitive mutants (9,18) have revealed that not all myristylated pp60-vrc proteins are membrane bound. Wild-type RSV-infected cells also contain small quantities of soluble pp60vsrc molecules, both in monomeric and pp50/pp9O complexed form, which are myristylated but not membrane bound (9). Moreover, myristate is attached to soluble cytoplasmic proteins as well as to membrane proteins (1,11,28,29).…”

VHY, a Novel Myristoylated Testis-restricted Dual Specificity Protein Phosphatase Related to VHX

“…They also differ strikingly in tissue distribution; VHY expressed at high levels only in the testis and at low levels in other tissues and cell types, whereas VHX is broadly expressed (29). The N termini of VHY and VHX contain a consensus myristoyl transferase recognition motif (35)(36)(37)(38) similar to that found in Src family kinases (35,39,40) and calcineurin B (36) and indeed are modified by myristic acid, presumably at Gly-2 (41). This modification correlates with the plasma membrane enrichment of VHY.…”

Role of p120ctn in Cadherin Mediated Suppression of Breast Cancer

“…Interestingly, pl20 was initially identified as a potent target of the Src tyrosine kinase (Reynolds et al, 1989). Src is normally tightly associated with membranes but can be rendered cytoplasmic by mutation of its NH 2 -terminal myristilation signal (Buss et al, 1984;Cross et al, 1984;Buss and Sefton, 1985;Kamps et al, 1985), and such mutants do not phosphorylate pl20 (Reynolds et al, 1989). Apparently, the opposite scenario is also true; i.e., rendering pl20 cytoplasmic by removing its cadherin anchor to the membrane eliminates most, if not all, of the otherwise extensive phosphorylation.…”