Probing conformational changes in orphan nuclear receptor: the NGFI-B intermediate is a partially unfolded dimer

Biophys Chem. 2008 Oct;137(2-3):81-7. doi: 10.1016/j.bpc.2008.07.005. Epub 2008 Jul 18.

Abstract

Human nerve growth factor-induced B (NGFI-B) is a member of the NR4A subfamily of orphan nuclear receptors (NRs). Lacking identified ligands, orphan NRs show particular co-regulator proteins binding properties, different from other NRs, and they might have a non-classical quaternary organization. A body of evidence suggests that NRs recognition of and binding to ligands, DNA, homo- and heterodimerization partners and co-regulator proteins involve significant conformational changes of the NR ligand-binding domains (LBDs). To shed light on largely unknown biophysical properties of NGFI-B, here we studied structural organization and unfolding properties of NGFI-B ligand (like)-binding domain induced by chemical perturbation. Our results show that NGFI-B LBD undergoes a two-state guanidine hydrochloride (GndHCl) induced denaturation, as judged by changes in the alpha-helical content of the protein monitored by circular dichroism spectroscopy (CD). In contrast, changes in the tertiary structure of NGFI-B LBD, reported by intrinsic fluorescence, reveal a clear intermediate state. Additionally, SAXS results demonstrate that the intermediate observed by intrinsic fluorescence is a partially folded homodimeric structure, which further unfolds without dissociation at higher GndHCl concentrations. This partially unfolded dimeric assembly of NGFI-B LBD might resemble an intermediate that this domain access momentarily in the native state upon interactions with functional partners.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Circular Dichroism
  • DNA-Binding Proteins / chemistry*
  • DNA-Binding Proteins / genetics
  • Guanidine / chemistry
  • Humans
  • Models, Molecular
  • Nuclear Receptor Subfamily 4, Group A, Member 1
  • Protein Conformation*
  • Protein Denaturation
  • Protein Folding
  • Protein Structure, Quaternary
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Receptors, Steroid / chemistry*
  • Receptors, Steroid / genetics
  • Recombinant Proteins / chemistry
  • Scattering, Radiation
  • Spectrometry, Fluorescence
  • X-Rays

Substances

  • DNA-Binding Proteins
  • NR4A1 protein, human
  • Nuclear Receptor Subfamily 4, Group A, Member 1
  • Receptors, Steroid
  • Recombinant Proteins
  • Guanidine