title: Binding of the N-terminal region of coactivator TIF2 to the intrinsically disordered AF1 domain of the glucocorticoid receptor is accompanied by conformational reorganizations.
abstract: Control of gene transcription by glucocorticoid receptors (GRs) is important for many physiological processes. Like other steroid hormone receptors, the regulation of target genes by GR is mediated by two transactivation domains: activation function 1 (AF1) in the N-terminal domain and AF2 in the C-terminal ligand-binding domain (LBD). Full receptor activity requires both AF1 and -2 plus assorted coregulatory proteins. Crystal structures of the ligand-bound LBD have provided insight regarding how AF2 interacts with specific coactivators. However, despite its being the major activation domain of GRs, knowledge of AF1 structure/function has languished. This is mainly because of the highly disorganized structure of the GR N-terminal domain. This lack of AF1 structure is shared by all members of the steroid/nuclear receptor superfamily for which it has been examined and AF1 is thought to allow productive interactions with assorted cofactors via protein-induced changes in secondary/tertiary structures. To date, there are no reports of a classical coactivator altering the secondary/tertiary structure of the GR AF1 domain. Earlier, we reported an N-terminal fragment of the p160 coactivator TIF2, called TIF2.0, that binds the GR N-terminal domain and alters GR transcriptional activity. We therefore proposed that TIF2.0 binding to AF1 changes both its conformation and transcriptional activity. We now report that TIF2.0 interacts with the GR AF1 domain to increase the amount of α-helical structure in the complex. Furthermore, TIF2 coactivator activity is observed in the absence of the GR LBD in a manner that requires the AF1 domain. This contrasts with previous models where TIF2 receptor interaction domains binding to GR LBD somehow alter AF1 conformation. Our results establish for the first time that coactivators can modify the structure of the AF1 domain directly via the binding of a second region of the coactivator and suggest a molecular explanation for how coactivators increase the transcriptional activity of GR-agonist complexes.
authors.affiliation: Department of Basic Sciences, The Commonwealth Medical College, Scranton, Pennsylvania 18509, USA.
authors.forename: Shagufta H
authors.initials: SH
authors.lastname: Khan
authors.forename: Smita
authors.initials: S
authors.lastname: Awasthi
authors.forename: Chunhua
authors.initials: C
authors.lastname: Guo
authors.forename: Devrishi
authors.initials: D
authors.lastname: Goswami
authors.forename: Jun
authors.initials: J
authors.lastname: Ling
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Griffin
authors.forename: S Stoney
authors.initials: SS
authors.lastname: Simons
authors.forename: Raj
authors.initials: R
authors.lastname: Kumar
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D051958:Nuclear Receptor Coactivator 2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: C498001:NCOA2 protein, human; C498003:Ncoa2 protein, rat; D051958:Nuclear Receptor Coactivator 2; D011965:Receptors, Glucocorticoid