Elbing K, et al. (2006) Subunits of the Snf1 kinase heterotrimer show interdependence for association and activity. J Biol Chem 281(36):26170-80
Abstract: The Snf1 kinase and its mammalian orthologue, the AMP-activated protein kinase (AMPK), function as heterotrimers composed of a catalytic alpha subunit and two non-catalytic subunits, beta and gamma. The beta subunit is thought to hold the complex together and control subcellular localization whereas the gamma subunit plays a regulatory role by binding to and blocking the function of an auto-inhibitory domain (AID) present in the alpha subunit. In addition, catalytic activity requires phosphorylation by a distinct upstream kinase. In yeast, any one of three Snf1-activating kinases, Sak1, Tos3 or Elm1, can fulfill this role. We have previously shown that Sak1 is the only Snf1-activating kinase that forms a stable complex with Snf1. Here we show that the formation of the Sak1-Snf1 complex requires the beta and gamma subunits in vivo. However, formation of the Sak1-Snf1 complex is not necessary for glucose regulated phosphorylation of the Snf1 activation loop. Snf1 kinase purified from cells lacking the beta subunits do not contain any gamma subunit, indicating that the Snf1 kinase does not form a stable alphagamma dimer in vivo. In vitro kinase assays using purified full-length and truncated Snf1 proteins demonstrate that the kinase domain, which lacks the AID, is significantly more active than the full-length Snf1 protein. Addition of purified beta and gamma subunits could stimulate the kinase activity of the full-length alpha subunit but only when all three subunits were present, suggesting an interdependence of all three subunits for assembly of a functional complex.
|Status: Published||Type: Journal Article||PubMed ID: 16847059|
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