Measuring the Orientation of Taurine in the Active Site of the Non-Heme Fe(II)/α-Ketoglutarate-Dependent Taurine Hydroxylase (TauD) Using Electron Spin Echo Envelope Modulation (ESEEM) Spectroscopy

The position and orientation of taurine near the non-heme Fe(II) center of the α-ketoglutarate (α-KG)-dependent taurine hydroxylase (TauD) was measured using Electron Spin Echo Envelope Modulation (ESEEM) spectroscopy. TauD solutions containing Fe(II), α-KG, and natural abundance taurine or specifically deuterated taurine were prepared anaerobically and treated with nitric oxide (NO) to make an S = 3/2 {FeNO}7 complex that is suitable for robust analysis with EPR spectroscopy. Using ratios of ESEEM spectra collected for TauD samples having natural abundance taurine or deuterated taurine, 1H and 14N modulations were filtered out of the spectra and interactions with specific deuterons on taurine could be studied separately. The Hamiltonian parameters used to calculate the amplitudes and line shapes of frequency spectra containing isolated deuterium ESEEM were obtained with global optimization algorithms. Additional statistical analysis was performed to validate the interpretation of the optimized parameters...