Using Intrinsic Fluorescence Emission Spectroscopy to Study Steroid Receptor and Coactivator Protein

X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy have proved powerful methods for studying the structure of the isolated ligand and DNA-binding domains of nuclear receptors. However, the N-terminal domain (NTD), which in some members of the superfamily is important for transcriptional regulation, and the full-length receptor proteins have proved more challenging. The NTD of different nuclear receptors show little sequence homology and can vary dramatically in length from a few to several hundred amino acids. Low resolution structural analysis using circular dichroism, NMR, steady-state fluorescence spectroscopy, and Fourier transformed infrared spectroscopy has provided valuable information on the conformation and folding of the structurally plastic NTD. In this chapter, we discuss protocols for measuring the intrinsic fluorescence emission spectrum for tryptophan residues under different experimental conditions of protein folding and unfolding.