POSTTRANSLATIONAL MODIFICATIONS OF THE 5'-AMP-ACTIVATED PROTEIN-KINASE BETA(1) SUBUNIT

The AMP-activated protein kinase (AMPK) consists of catalytic Lu and n oncatalytic beta and gamma subunits and is responsible for acting as a metabolic sensor for AMP levels, There are multiple genes for each su bunit and the rat liver AMPK alpha(1) and alpha(2), catalytic subunits are associated with beta(1) and gamma(1) noncatalytic subunits. We fi nd that the isolated gamma(1) subunit is N-terminally acetylated with no other posttranslational modification, The isolated beta(1) subunit is N-terminally myristoylated, Transfection of COS cells with AMPK sub unit cDNAs containing a non-myristoylatable beta(1) reduces, but does not eliminate, membrane binding of AMPK heterotrimer, The isolated bet a(1) subunit is partially phosphorylated at three sites, Ser(24/25), S er(182), and Ser(108). The Ser(24/25) and Ser(108) sites are substoich iometrically phosphorylated and can be autophosphorylated in vitro. Th e Ser-Pro site in the se quence LSSS(182)PPGP is stoichiometrically ph osphorylated, and no additional phosphate is incorporated into this si te with autophosphorylation, Based on labeling studies in transfected cells, we conclude that alpha(1) Thr(172) is a major, although not exc lusive, site of both basal and stimulated alpha(1) phosphorylation by an upstream AMPK kinase.