ATOMIC STRUCTURES OF THE RAPAMYCIN ANALOGS IN COMPLEX WITH BOTH HUMAN FKBP12 AND FRB DOMAIN OF FRAP
[FKB1A_HUMAN] Keeps in an inactive conformation TGFBR1, the TGF-beta type I serine/threonine kinase receptor, preventing TGF-beta receptor activation in absence of ligand. Recruites SMAD7 to ACVR1B which prevents the association of SMAD2 and SMAD3 with the activin receptor complex, thereby blocking the activin signal. May modulate the RYR1 calcium channel activity. PPIases accelerate the folding of proteins. It catalyzes the cis-trans isomerization of proline imidic peptide bonds in oligopeptides.  [FRAP_HUMAN] Serine/threonine protein kinase which is a central regulator of cellular metabolism, growth and survival in response to hormones, growth factors, nutrients, energy and stress signals. Functions as part of 2 structurally and functionally distinct signaling complexes mTORC1 and mTORC2 (mTOR complex 1 and 2). Activated mTORC1 up-regulates protein synthesis by phosphorylating key regulators of mRNA translation and ribosome synthesis. This includes phosphorylation of EIF4EBP1 and release of its inhibition toward the elongation initiation factor 4E (eiF4E). Moreover, phosphorylates and activates RPS6KB1 and RPS6KB2 that promote protein synthesis by modulating the activity of their downstream targets including ribosomal protein S6, eukaryotic translation initiation factor EIF4B and the inhibitor of translation initiation PDCD4. Regulates ribosome synthesis by activating RNA polymerase III-dependent transcription through phosphorylation and inhibition of MAF1 a RNA polymerase III-repressor. In parallel to protein synthesis, also regulates lipid synthesis through SREBF1/SREBP1 and LPIN1. To maintain energy homeostasis mTORC1 may also regulate mitochondrial biogenesis through regulation of PPARGC1A. mTORC1 also negatively regulates autophagy through phosphorylation of ULK1. Under nutrient sufficiency, phosphorylates ULK1 at 'Ser-758', disrupting the interaction with AMPK and preventing activation of ULK1. Also prevents autophagy through phosphorylation of the autophagy inhibitor DAP. mTORC1 exerts a feedback control on upstream growth factor signaling that includes phosphorylation and activation of GRB10 a INSR-dependent signaling suppressor. Among other potential targets mTORC1 may phosphorylate CLIP1 and regulate microtubules. As part of the mTORC2 complex MTOR may regulate other cellular processes including survival and organization of the cytoskeleton. Plays a critical role in the phosphorylation at 'Ser-473' of AKT1, a pro-survival effector of phosphoinositide 3-kinase, facilitating its activation by PDK1. mTORC2 may regulate the actin cytoskeleton, through phosphorylation of PRKCA, PXN and activation of the Rho-type guanine nucleotide exchange factors RHOA and RAC1A or RAC1B. mTORC2 also regulates the phosphorylation of SGK1 at 'Ser-422'.               
Publication Abstract from PubMed
The structure of the FKBP12-rapamycin-FRB ternary complex has now been refined at 2.2 A resolution. The cell-cycle arrest agent rapamycin binds FK506-binding protein (FKBP12) and the FKBP12-rapamycin binding (FRB) domain of FKBP12-rapamycin associated protein (FRAP) simultaneously, and the inhibition of FRAP is responsible for rapamycin's biological activity. The conformation of rapamycin in the ternary complex is very similar to that observed in the FKBP12-rapamycin binary complex, with an r.m.s. difference of only 0.30 A. However, a slight (9 degrees ) rotation repositions the FRB-binding face of rapamycin in the ternary complex. There are extensive rapamycin-protein interactions and relatively few interactions between the two protein partners FKBP12 and FRB, these interactions mainly involving residues in the 40s and 80s loops of FKBP12 and alpha1 and alpha4 of FRB. The high-resolution refinement has revealed the crucial role of several buried waters in the formation of the ternary complex.
Refined structure of the FKBP12-rapamycin-FRB ternary complex at 2.2 A resolution.,Liang J, Choi J, Clardy J Acta Crystallogr D Biol Crystallogr. 1999 Apr;55(Pt 4):736-44. PMID:10089303
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.