A dual plasmid system was used to examine the protein and acyl-CoA specificities of Saccharomyces cerevisiae myristoyl-CoA:protein N-myristoyltransferase (NMT) by co-expressing it in Escherichia coli with each of four homologous α subunits of the signal-transducing, heterotrimeric G proteins. Exogenous [3H]myristate was incorporated into rat G(iα1) and rat G(oα) but not into bovine G(sα) or human G(zα). Oxygen for methylene group substitutions in myristate result in analogs with comparable chain length and stereochemistry but marked reductions in hydrophobicity. Metabolic labeling studies with 6-, 11-, or 13-[3H]oxatetradecanoic acid indicated that they were incorporated into rat G(iα1) and G(oα) with an efficiency that could be correlated with their accumulation into E. coli and their interactions with purified NMT in vitro. Octapeptides derived from the NH2-terminal sequences of these four G(α) polypeptides were tested as substrates for purified S. cerevisiae NMT. None were bound by the enzyme. Acidic residues at positions 7 and 8 appear to contribute to this effect; deletion of these two amino acids or addition of the next 9 residues of rat G(oα) produced active substrates. These results imply that productive interactions between NMT and G(α) protein substrates in vivo require structural features that are not fully represented within their NH2-terminal 8 residues.
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - 1991|