4l3j
Crystal structures of human p70S6K1 kinase domainCrystal structures of human p70S6K1 kinase domain
Structural highlights
FunctionKS6B1_HUMAN Serine/threonine-protein kinase that acts downstream of mTOR signaling in response to growth factors and nutrients to promote cell proliferation, cell growth and cell cycle progression. Regulates protein synthesis through phosphorylation of EIF4B, RPS6 and EEF2K, and contributes to cell survival by repressing the pro-apoptotic function of BAD. Under conditions of nutrient depletion, the inactive form associates with the EIF3 translation initiation complex. Upon mitogenic stimulation, phosphorylation by the mammalian target of rapamycin complex 1 (mTORC1) leads to dissociation from the EIF3 complex and activation. The active form then phosphorylates and activates several substrates in the preinitiation complex, including the EIF2B complex and the cap-binding complex component EIF4B. Also controls translation initiation by phosphorylating a negative regulator of EIF4A, PDCD4, targeting it for ubiquitination and subsequent proteolysis. Promotes initiation of the pioneer round of protein synthesis by phosphorylating POLDIP3/SKAR. In response to IGF1, activates translation elongation by phosphorylating EEF2 kinase (EEF2K), which leads to its inhibition and thus activation of EEF2. Also plays a role in feedback regulation of mTORC2 by mTORC1 by phosphorylating RICTOR, resulting in the inhibition of mTORC2 and AKT1 signaling. Mediates cell survival by phosphorylating the pro-apoptotic protein BAD and suppressing its pro-apoptotic function. Phosphorylates mitochondrial URI1 leading to dissociation of a URI1-PPP1CC complex. The free mitochondrial PPP1CC can then dephosphorylate RPS6KB1 at 'Thr-412', which is proposed to be a negative feedback mechanism for the RPS6KB1 anti-apoptotic function. Mediates TNF-alpha-induced insulin resistance by phosphorylating IRS1 at multiple serine residues, resulting in accelerated degradation of IRS1. In cells lacking functional TSC1-2 complex, constitutively phosphorylates and inhibits GSK3B. May be involved in cytoskeletal rearrangement through binding to neurabin.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] Publication Abstract from PubMedThe activity of the ribosome protein subunit 6 kinase 1 (S6K1) is stimulated by phosphorylation of Thr389 in the hydrophobic motif by mTORC1 and phosphorylation of Thr229 in the activation loop by PDK1; however, the order of the two events is still ambiguous. Here we report six crystal structures of the S6K1 kinase domain alone or plus the hydrophobic motif in various forms, in complexes with a highly specific inhibitor. The structural data together with the biochemical data reveal in vivo phosphorylation of Thr389 in the absence of Thr229 phosphorylation and demonstrate the importance of two conserved residues, Gln140 and Arg121, in the establishment of a hydrogen-bonding network between the N-lobe and the hydrophobic motif. Phosphorylation of Thr389 or introduction of a corresponding negatively charged group leads to reinforcement of the network and stabilization of helix alphaC. Furthermore, comparisons of S6K1 with other AGC family kinases suggest that the structural and sequence differences in the hydrophobic motif and helix alphaC account for their divergence in PDK1 dependency. Together, these results indicate that phosphorylation of the hydrophobic motif in S6K1 is independent of and probably, precedes and promotes phosphorylation of the activation loop. Crystal structures of S6K1 provide insights into the regulation mechanism of S6K1 by the hydrophobic motif.,Wang J, Zhong C, Wang F, Qu F, Ding J Biochem J. 2013 Jun 3. PMID:23731517[15] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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