The Conformation of the Glucocorticoid Receptor AF1/tau1 Domain Induced by Osmolyte Binds Co-regulatory Proteins

Abstract

The activation domains of many transcription factors appear to exist naturally in an unfolded or only partially folded state. This seems to be the case for AF1/tau1, the major transactivation domain of the human glucocorticoid receptor. We show here that in buffers containing the natural osmolyte trimethylamine N-oxide (TMAO), recombinant AF1 folds into more a compact structure, as evidenced by altered fluorescence emission, circular dichroism spectra, and ultracentrifugal analysis. This conformational transition is cooperative, a characteristic of proteins folding to natural structures. The structure resulting from incubation in TMAO causes the peptide to resist proteolysis by trypsin, chymotrypsin, endoproteinase Arg-C and endoproteinase Gluc-C. Ultracentrifugation studies indicate that AF1/tau1 exists as a monomer in aqueous solution and that the presence of TMAO does not lead to oligomerization or aggregation. It has been suggested that recombinant AF1 binds both the ubiquitous coactivator CBP and the TATA boxbinding protein, TBP. Interactions with both of these are greatly enhanced in the presence of TMAO. Co-immunoadsorption experiments indicate that in TMAO each of these and the coactivator SRC-1 are found complexed with AF1. These data indicate that TMAO induces a conformation in AF1/tau1 that is important for its interaction with certain co-regulatory proteins.

TATA box binding protein induces structure in the recombinant glucocorticoid receptor AF1 domain

“…We recently demonstrated that the recombinant GR AF1 adopts a native-like folded conformation when incubated in the presence of the naturally occurring osmolyte, trimethylamine N-oxide, and in this folded conformation it strongly interacts with certain specific coregulatory proteins. These include the TATA box binding protein (TBP), the CREB binding protein, and steroid receptor coactivator 1 (22). Taken together, the data strongly suggest that proper folding of AF1 is an important requirement for its actions in regulating transcription.…”

“…When expressed independently, the GR AF1 shows little structure and seems to exist as an ensemble of largely unstructured conformers (17, 18). The GR AF1 is known to interact with other transcription factors, and conditional folding has been suggested to be the key for these interactions (19)(20)(21)(22).…”

“…When expressed independently, the GR AF1 shows little structure and seems to exist as an ensemble of largely unstructured conformers (17, 18). The GR AF1 is known to interact with other transcription factors, and conditional folding has been suggested to be the key for these interactions (19)(20)(21)(22).It has been reported that in the presence of trifluoroethanol, the ''core'' of AF1 (AF1 c , amino acids 187-242), located toward the C-terminal end of AF1, adopts three helical segments (17). Independent experiments have shown that substitution of the ␣-helixbreaking amino acid proline for natural residues at critical positions in these putative helices significantly reduces the transcriptional potency of the GR (17).…”

“…It is interesting that the GR AF1 can interact directly with TBP (22,25), the critical protein that forms the basis for the multiprotein transcription initiation complex. This direct interaction between AF1 and TBP is not part of currently popular models for transcriptional regulation by the GR (29).…”

Role of androgen receptor polyQ chain elongation in Kennedy's disease and use of natural osmolytes as potential therapeutic targets

“…4. Because of their flexible structures, intrinsically disordered regions/domains of many signaling proteins including AR NTD/AF1 are capable of creating favorable surfaces for their efficient interactions with their target proteins (39) and can also be induced to fold spontaneously to native, functional forms by addition of certain osmolytes to the solvent (40,41). In this osmolyte-induced conformation, NTD/AF1 of the AR binds strongly to SRC-1 (41).…”