Myristoylated alpha subunits of guanine nucleotide-binding regulatory proteins.

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Abstract
Antisera directed against specific subunits of guanine nucleotide-binding regulatory proteins (G proteins) were used to immunoprecipitate these polypeptides from metabolically labeled cells. This technique detects, in extracts of a human astrocytoma cell line, the .alpha. subunits of Gs (stimulatory) (.alpha.45 and .alpha.52), and 41-kDa subunit of Gi (inhibitory) (.alpha.41), a 40-kDa protein (.alpha.40), and the 36-kDa .beta. subunit. No protein that comigrated with the .alpha. subunit of G0 (unknown function) (.alpha.39) was detected. In cells grown in the presence of [3H]myristic acid, .alpha.41 and .alpha.40 contained 3H label, while the .beta. subunit did not. Chemical analysis of lipids attached covalently to purified .alpha.41 and .alpha.39 from bovine brain also revealed myristic acid. Similar analysis of brain G protein .beta. and .gamma. subunits and of Gt (transducin) subunits (.alpha., .beta., and .gamma.), failed to reveal fatty acids. The fatty acid associated with .alpha.41, .alpha.40, and .alpha.39 was stable to treatment with base, suggesting that the lipid is linked to the polypeptide via an amide bond. These GTP binding proteins are thus identified as members of a select group of proteins that contains myristic acid covalently attached to the peptide backbone. Myristate may play an important role in stabilizing interactions of G proteins with phospholipid or with membrane-bound proteins.