Resonance Raman spectra of blue copper proteins: Variable temperature spectra of Thermus thermophilus HB27 laccase

The resonance Raman (rR) spectra of the oxidized type 1 copper active site (Cu_T1) in Thermus thermophilus HB27 laccase (Tth-lac) has been determined in the 20 to 80 °C temperature range using 633-nm excitation. The positions and relative intensities of rR peaks are virtually independent of temperature, indicating that Cu_T1 ligation is robust over the investigated range. The intensity-weighted average of Tth-lac Cu-S_Cys vibrations (<ν(Cu-S_Cys)>) = 423 cm⁻¹) is higher than those of most cupredoxins but is comparable to those of other multicopper oxidases (MCOs). <ν(Cu-S_Cys)> values for Tth-lac and several Cu_T1 centers in cupredoxins and MCOs do not correlate well with Cu-S_Cys bond lengths but do exhibit systematic trends with redox thermodynamic properties.

Prologue

F. Ann Walker was a great scholar and dear friend. While at Columbia in the early 1960s, I (HBG) followed her graduate work at Brown on the effects of axial ligands on vanadyl ion EPR spectra. Dick Carlin, her thesis adviser, invited me to serve as external member of her thesis committee. I joined, made my way to Providence, met her just before the exam, and greatly admired (enjoyed!) her thoughtful responses to questions from physical chemists about metal-oxo electronic structures. Our friendship grew stronger over the years, enhanced by lively discussions of heme protein chemistry in San Francisco, Pasadena, Tucson, and at Gordon Research Conferences. Ann was a superstar in biological inorganic chemistry. She will be sorely missed but not forgotten.