A time-resolved fluorescence study of human copper-zinc superoxide dismutase

Abstract

Superoxide dismutase; Time-resolved fluorescence: Fluorescence lifetime distribution; (Human)The intrinsic fluorescence decay of human Cu,Zn superoxide dismutase was measured by frequency-domain techniques. The protein consists of two subunits, each containing one tryptophsn and no tyrosine residues. Using a synchrotron radiation source, which allows facile selection of the excitation wavelength, the dependence of the emission decay upon excitation was studied. No significant excitation wavelength effects were found The two vvptophans contained in the dimer, although fully equivalent and exposed to solvent, showed a fluorescence decay that cannot be described by a single lifetime. Either two lifetimes. or one Lorentzian-shaped continuous distribution of lifetimes, are needed to obtain a good fit. Under identical experimental conditions, control experiments showed that N-acetyltryptophanamide, an analogue of tryptophanyl residues in proteins, decays with a single lifetime. The hetero~eous decay of tryptophan fluoresce& in superoxide dismutase is interpreted as due to the,presence of static and/or dynamic conformers in the protein that deMy with different lifetimes. The two models of discrete lifetimes and continuous distribution of lifetimes are discussed with reference to measurements on holo-and ape-human superoxide dismutase.

Conformational dynamics of bovine Cu, Zn superoxide dismutase revealed by time-resolved fluorescence spectroscopy of the single tyrosine residue

“…Increasing temperature decreased both the average lifetime and the heterogeneity of the decay (width of the lifetime distribution). Similar temperature effects have been described for the homologous protein, human SOD (Rosato et al, 1990b), and for whiting parvalbumin (Ferreira, 1989). In those studies, the behavior of the width of the lifetime distribution as a function of temperature has been explained in terms of a temperature effect on the rates of interconversion between conformational substates in the proteins.…”

DJ-1 Is a Copper Chaperone Acting on SOD1 Activation

“…A significant fluorescence quenching for the holo- compared with the apo-SOD1 protein has already been reported in the literature (44). Although most of the fluorescence quenching effects reported in literature are ascribed to the Cu(II) ion, it has been reported that the effect induced by Cu(I) ion is the same as the one induced by Cu(II) ion, as for instance reported for the type 1 copper protein azurin (45).…”

Fluorescence lifetime distribution of folded and unfolded proteins

“…Fluorescence emission spectra of native and metal-depleted HSOD are structureless, centered at 344 nm, and similar to the spectrum of N-acetyltryptophanamide (NATA) [25]. The relative fluorescence intensity of holo and apo protein at 344 nm is reported in Figure l(a) as a function of GdHCl or urea concentration.…”