Human
myristoyl-CoA synthetase and
myristoyl-CoA:protein N-myristoyltransferase (hNmt) have been partially purified from an
erythroleukemia cell line. Their substrate specificities were examined using two in vitro assays of
enzyme activity together with a panel of C7-C17
saturated fatty acids plus 72
myristic acid analogs containing
oxygen,
sulfur, ketocarbonyl,
ester,
amide, cis and trans double bonds, triple bonds, and para-substituted phenyl groups. There is an inverse relationship between the polarity and the activity of C14
fatty acid substrates of
myristoyl-CoA synthetase. Surveys of tetradecenoic and tetradecynoic
acids suggest that
myristate is bound to the
synthetase in a bent conformation with a principal bend occurring in the vicinity of C5-C6. The
synthetase can tolerate a somewhat wider range of physical chemical properties in acyl chains than can the monomeric hNmt. However, like
myristoyl-CoA synthetase, there is an inverse relationship between acyl chain polarity and the activities of hNmt's
acyl-CoA substrates. Moreover, the acyl chain of
myristoyl-CoA appears to be bound to hNmt in a bent conformation with
bends located in the vicinity of C5 and C8. The acyl chain specificities of both
enzymes make them well suited to utilize efficiently any cellular pools of 5Z-tetradecenoic and 5Z,8Z-tetradecadienoic
acids and their
CoA derivatives. This feature may account for the recent observation that in some mammalian cell lineages, certain N-myristoyl-
proteins are heterogeneously acylated with these C14
fatty acids. Finally, the
acyl-CoA binding sites of human and Saccharomyces cerevisiae Nmts appear to have been highly conserved. Given their overlapping yet distinct
peptide substrate specificities, development of species-specific inhibitors of Nmts should probably focus on structural features recognized in the
enzymes'
peptide substrates rather than in the acyl chain of their
acyl-CoA substrates.