Thermodynamic Dissection of the Intrinsically Disordered N-terminal Domain of Human Glucocorticoid Receptor

Jing Li,Hesam N Motlagh,Carolyn Chakuroff,E Brad Thompson,Vincent J Hilser

doi:10.1074/jbc.m112.355651

Abstract

Intrinsically disordered (ID) sequence segments are abundant in cell signaling proteins and transcription factors. Because ID regions commonly fold as part of their intracellular function, it is crucial to understand the folded states as well as the transitions between the unfolded and folded states. Specifically, it is important to determine 1) whether large ID segments contain different thermodynamically and/or functionally distinct regions, 2) whether any ID regions fold upon activation, 3) the degree of coupling between the different ID regions, and 4) whether the stability of ID domains is a determinant of function. In this study, we thermodynamically characterized the full-length ID N-terminal domain (NTD) of human glucocorticoid receptor (GR) and two of its naturally occurring translational isoforms. The protective osmolyte trimethylamine N-oxide (TMAO) was used to induce folding transitions. Each of the three NTD isoforms was found to undergo a cooperative folding transition that is thermodynamically indistinguishable (based on m-values) from that of a globular protein of similar size. The extrapolated stabilities for the NTD isoforms showed clear correlation with the known activities of their corresponding GR translational isoforms. The data reveal that the full-length NTD can be viewed as having at least two thermodynamically coupled regions, a functional region, which is indispensable for GR transcriptional activity, and a regulatory region, the length of which serves to regulate the stability of NTD and thus the activity of GR. These results suggest a new functional paradigm whereby steroid hormone receptors in particular and ID proteins in general can have multiple functionally distinct ID regions that interact and modulate the stability of important functional sites.

Highlights

Glucocorticoid receptor (GR) translational isoforms with different lengths in the intrinsically disordered (ID) N-terminal domain (NTD) have different activities
The data reveal that the full-length NTD can be viewed as having at least two thermodynamically coupled regions, a functional region, which is indispensable for GR transcriptional activity, and a regulatory region, the length of which serves to regulate the stability of NTD and the activity of GR
Occurring Osmolyte trimethylamine N-oxide (TMAO) Can Induce Cooperative Folding Transitions in the ID NTDs of Different GR Translational Isoforms—Tryptophan emission spectra were measured for the GR A-NTD, GR C2-NTD, and GR C3-NTD constructs in buffers with different TMAO concentrations using an excitation wavelength of 295 nm. (Note that all three constructs contain two Trp residues, corresponding to positions 213 and 364 as numbered in the full-length GR A-NTD)

Summary

Introduction

Glucocorticoid receptor (GR) translational isoforms with different lengths in the intrinsically disordered (ID) N-terminal domain (NTD) have different activities. The fact that the GR NTD constructs and the known globular proteins could be fit to the same linear relationship indicates that TMAO affects the folded and unfolded states of ID and globular proteins to a similar degree on a per amino acid basis [12] even if the molecular basis of these effects are not known (see Fig. 6 and “Discussion”).

Results

Conclusion