Quantifying Disorder Of An Intrinsically Unstructured Domain In Estrogen Receptor

The N-terminal domain (NTD) of estrogen receptor is a hallmark of the receptor's transactivation function. While it is viewed as intrinsically disordered, the molecular knowledge about its disorderness is still limited. Here, we examine the NTD unfolding by chemical denaturants using circular dichroism (CD), small-angle X-ray scattering (SAXS), nuclear magnetic resonance (NMR), and molecular dynamics (MD) simulation. The change at 222 nm of CD signals and disappearance of N15-NMR peaks show the increased unfoldedness of the already unstructured NTD, while SAXS demonstrates its molecular size in Rg increased from 32 Å to 58 Å induced by 6-M guanidine hydrochloride, accompanied by substantial broadening of pair-wise distance distribution. Combination of SAXS data with replica exchange MD simulations further reveals that the NTD undergoes a large-scale structural change from a relatively compact to an elongated conformation. Collectively, these results provide an alternative view of the NTD structural disorder as being as an unstructured, yet relatively compact structure-ensemble.