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The SNF1/AMP-activated protein kinases are αβγ-heterotrimers that sense and regulate energy status in eukaryotes. They are activated by phosphorylation of the catalytic Snf1/α subunit, and the Snf4/γ regulatory subunit regulates phosphorylation through adenine nucleotide binding. In Saccharomyces cerevisiae, the Snf1 subunit is phosphorylated on the activation-loop Thr-210 in response to glucose limitation. To assess the requirement of the heterotrimer for regulated Thr-210 phosphorylation, we examined Snf1 and a truncated Snf1 kinase domain (residues 1-309) that has partial Snf1 function. Snf1(1-309) does not interact with the β and Snf4/γ regulatory subunits, and its activity was independent of them in vivo. Phosphorylation of both Snf1 and Snf1(1-309) increased in response to glucose limitation in wild-type cells and in cells lacking β- and Snf4/γ-subunits. These results indicate that glucose regulation of activation-loop phosphorylation can occur by mechanism(s) that function independently of the regulatory subunits. We further show that the Reg1-Glc7 protein phosphatase 1 and Sit4 type 2A-like phosphatase are largely responsible for dephosphorylation of Thr-210 of Snf1(1-309). Together, these findings suggest that these two phosphatases mediate heterotrimer-independent regulation of Thr-210 phosphorylation.

Citation

Amparo Ruiz, Yang Liu, Xinjing Xu, Marian Carlson. Heterotrimer-independent regulation of activation-loop phosphorylation of Snf1 protein kinase involves two protein phosphatases. Proceedings of the National Academy of Sciences of the United States of America. 2012 May 29;109(22):8652-7

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PMID: 22589305

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