Novel fatty acyl substrates for myristoyl-CoA:protein N-myristoyl-transferase

Myristoyl-CoA:protein N-myristoyltransferase (NMT) catalyzes the covalent attachment of myristic acid to the NH₂-terminal Gly residues of a number of viral and cellular proteins. The remarkable specificity of this enzyme for myristoyl CoA observed in vivo appears to arise in large part from a cooperativity beteen NMTs acylCoA and peptide binding sites: the length of the acylCoA bound to NMT influences the interactions of peptide substrates with NMT. We have previously synthesized analogs of myristic acid with single oxygen or sulfur for methylene substitutions. These heteroatom substitutions produce significant reductions in acyl chain hydrophobicity without accompanying alterations in chain length or stereochemical restrictions. In vitro studies have shown that the CoA thioesters of these analogs are substrates for S. cervisiae NMT and that the efficiency of their transfer to octapeptide substrates is peptide sequence-dependent. In vivo studies with cultured mammalian cells have confirmed that these fatty acid analogs are selectively incorporated into a subset of cellular N-myristoylproteins, that only a subset of analog-substituted proteins undergo redistribution from membrane to cytosolic fractions, and that these analogs can inhibit the replication of human immunodeficiency virus I and Moloney murine leukemia viruses - two retroviruses that depend upon N-myristoylation of their gag polyprotein precursors for assembly. We have now extended our analysis of NMT-acylCoA interactions by synthesizing additional analogs of myristic acid and testing them in a coupled in vitro assay system. Myristic analogs with two oxygen or two sulfur substitutions have hydrophobicities comparable to that of hexanoic acid and decanoic acid, respectively. Despite this large reduction in hydrophobicity, they are utilized as substrates by S. cerevisiae NMT in vitro, albeit less efficiently than the single heteroatom-substituted compounds. The branched chain fatty acids isomyristic acid and anteisopentadecanoic acid are remarkably good NMT substrates. In addition, two aromatic ring-containing myristic acid analogs will serve as substrates for NMT. Introduction of a cis double bond between carbons 8 and 9 of the aromatic fatty acid analog 11-phenylundecanoic acid makes this compound a much better substrate for NMT. The data confirm that the acylCoA bound to NMT can dramatically influence the interaction of NMT with synthetic octapeptide substrates. These novel NMT substrates, which differ markedly in their physical-chemical properties from myristic acid, may represent useful compounds for investigating the role of fatty acylation in protein targeting and function.