Lipid modifications of G protein subunits: Myristoylation of G(oα) increases its affinity for βγ

Myristoylated recombinant proteins can be synthesized in Escherichia coli by concurrent expression of the enzyme myristoyl-CoA:protein N-myristoyl-transferase with its protein substrates (Duronio, R.J., Jackson-Machelski, E., Heuckeroth, R.O., Olins, P.O., Devine, C.S., Yonemoto, W., Slice, L.W., Taylor, S. S., and Gordon, J.I. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 1506-1510). Expression of the G protein subunit G(oα) in this system results in the synthesis of two forms of the protein; these were separated on a column of heptylamine-Sepharose. Purification of the more abundant form of G(oα) yielded a product that has a blocked amino terminus. Chemical analysis of the fatty acids released by acid hydrolysis of the protein revealed myristic acid. The second form of the protein was not myristoylated. Myristoylated and nonmyristoylated recombinant G(oα) were compared with brain G(oα) (which is myristoylated) for their ability to interact with G protein βγ subunits. The nonmyristoylated recombinant protein clearly had a reduced affinity for βγ, while the myristoylated recombinant protein was indistinguishable from native G(oα) in its subunit interactions. Thus, myristoylation increases the affinity of α subunits for βγ. We propose that the function of myristoylation of G protein α subunits is, at least in part, to facilitate formation of the heterotrimer and the localization of α to the plasma membrane.