Regulation of 5′-AMP-activated Protein Kinase Activity by the Noncatalytic β and γ Subunits

作者：Jason R.B. Dyck, Guang xun Gao, Jane Widmer, David Stapleton, Carolina Fernández, Bruce E. Kemp, Lee A. Witters · 发表于：Journal of Biological Chemistry · 年份：1996 · DOI：10.1074/jbc.271.30.17798 · 被引用次数：186 · 研究领域：Metabolism, Diabetes, and Cancer、Biochemical and Molecular Research、Cancer, Hypoxia, and Metabolism

The mammalian 5'-AMP-activated protein kinase is a heterotrimer consisting of an alpha catalytic subunit and beta and gamma noncatalytic subunits, each of which is represented in a larger isoprotein family, related to the SNF1 kinase and its interacting proteins in yeast. In this study, we have used mammalian cell transfection to compare the activities of the two alpha subunit isoforms, alpha-1 and alpha-2, and to study the influence of the noncatalytic subunits on enzyme subunit association and activity. Expression of epitope-tagged protein subunits in COS7 cells indicates detectable but low level kinase activity for each of the two catalytic alpha subunits. Co-expression of alpha subunits with the beta or gamma subunits modestly increases kinase activity accompanied by the formation of alpha/beta or alpha/gamma heterodimers. Co-expression of all three subunits, however, is accompanied by a 50-110-fold increase in kinase activity with the formation of a heterotrimeric complex. In addition to binding of each noncatalytic subunit to the alpha subunit, the beta and gamma subunits bind to each other, likely resulting in a more stable heterotrimeric complex. The increase in kinase activity associated with expression of this heterotrimer is due both to an increase in enzyme-specific activity (units/enzyme mass) and to an apparent enhanced alpha subunit expression. Co-expression of a catalytically defective alpha subunit or the beta/gamma-binding COOH-terminal domain of the alpha s...