Metal and substrate binding to an Fe(II) dioxygenase resolved by UV spectroscopy with global regression analysis

The addition of divalent metal ions or substrate taurine to TauD, an alpha-ketoglutarate-dependent dioxygenase, alters its UV absorption, as clearly observed by monitoring the protein's difference spectra. Binding of metal ions leads to a decrease in absorption at similar to 297 nm and modulation of other features. A separate signature with enhanced absorption at similar to 295 nm is identified for binding of taurine. These narrow (similar to 700 cm(-1)) and intense (similar to 0.5 mM(-1) cm(-1)) spectral changes are attributed to ligand-induced protein conformational changes affecting the environment of aromatic residues. The changes in the UV difference spectra were exploited to assess directly the thermodynamics and kinetics of ligand interactions in wildtype TauD and selected variants. This approach holds promise as a new tool to probe ligand-induced conformational changes in a wide range of other proteins. Experimental and quantification approaches for a reliable analysis of protein absorption below 320 nm are presented. (C) 2009 Elsevier Inc. All rights reserved.