Heteroatom-substituted fatty acid analogs as substrates for N-myristoyltransferase: an approach for studying both the enzymology and function of protein acylation

Myristoyl-CoA:protein N-myristoyltransferase (NMT), the Enzyme that transfers the myristoyl (14:0) moiety from myristoyl CoA thioester to nascent proteins, is remarkably specific for both peptide and fatty acyl CoA substrates. To investigate the interaction of NMT with fatty acyl CoA substrates, we have synthesized 10 oxygen- or sulfur-substituted fatty acid analogs. These analogs differ dramatically in hydrophobicity from naturally occurring fatty acids of similar length. As acylpeptides, sulfur-substituted myristic acid analogs migrate on reverse-phase HPLC like 11:0 or 12:0 fatty acids, while oxygen-substituted analogs migrate like 9:0 to 11:0 fatty acids. CoA thioesters of several of these analogs serve as good NMT substrates in vitro, implying that NMT selects fatty acyl substrates primarily on the basis of chain length rather than hydrophobicity. Myristelaidoyl (14:1, delta 9,10-trans) CoA is also a significantly better substrate than myristoleoyl (14:1, delta 9,10-cis) CoA. The fatty acyl group bound to NMT profoundly influences the rate of acylpeptide formation and the affinity of NMT for peptide substrates. However, the peptide substrate bound to NMT does not produce significant alterations in the enzyme's affinity for myristoyl CoA. In vitro characterization of these heteroatom substituted analogs suggests that they will be efficiently incorporated into proteins in vivo and may markedly alter acylprotein targeting and function.