DETERGENT BINDING TO UNMYRISTYLATED PROTEIN-KINASE-A - STRUCTURAL IMPLICATIONS FOR THE ROLE OF MYRISTATE

Myristylation often governs the targeting of protein kinases to the pl asma membrane. It is now known that a key member of the src family of protein tyrosine kinases, pp60(v-src), binds to the lipid bilayer of t he plasma membrane via a myristylated amino terminal sequence. The mec hanism of this interaction is not known; however, myristic acid (Myris tic acid may also be referred to as Myristate) and residues 2 through 14 are also absolutely required (Resh and Ling, 1990). This review pre sents an analysis of crystal structures of detergent-modified recombin ant and myristylated mammalian catalytic subunit of protein kinase A. Crystals of unmyristylated recombinant catalytic subunit of protein ki nase A are grown in the presence of Mega 8, a glucamide-type of deterg ent, and only this detergent binds, which results in a resolution exte nsion (Knighton et al., 1991a). Comparisons of these two structures re veal that the detergent association with the recombinant enzyme binds in exactly the same hydrophobic pocket of the protein occupied by myri stic acid in the mammalian protein (Karlsson et al., 1993; Zheng et al ., 1993a). Removal of the detergent through soaking results in the loc al unwinding of the first helix, helix A, and disorder of the canonica l recognition sequence of the phosphorylation site, Ser 10 (Zheng et a l., 1993b), These results suggest that anchoring the myristic acid ins ide the protein results in formation of a stable structural template, which includes the myristylated amino terminal sequence important for the recognition by protein kinases. This ''inside out'' motif might pr ovide a structural paradigm for the recognition of myristylated protei ns, including pp60(v-src).