A step toward the prediction of the fluorescence lifetimes of tryptophan residues in proteins based on structural and spectral data

A method is presented that allows the calculation of the lifetimes of trypt ophan residues on the basis of spectral and structural data. It is applied to two different proteins. The calcium binding protein from the sarcoplasm of the muscles of the: sand worm Nereis diversicolor (NSCP) changes its con formation upon binding of Ca2+ or Mg2+ NSCP contains three tryptophan resid ues at position 4, 57, and 170, respectively. The fluorescence lifetimes of W57 are investigated in a mutant in which W4 and W170 have been replaced. The time resolved fluorescence properties of W57 are linked to its differen t microconformations, which were determined by a molecular dynamics simulat ion map. Together with the determination of the radiative rate constant fro m the wavelength of maximum intensity of the decay associated spectra, it w as possible to determine an exponential relation between the nonradiative r are constant and the distance between the indole CE3 atom and the carbonyl carbon of the peptide bond reflecting a mechanism of electron transfer as t he main determinant of the value for the nonradiative rate constant. This r esult allows the calculation of the fluorescence lifetimes from the protein structure and the spectra. This method was further tested for the tryptoph an of Pin-ras p21 (W32) and for W43 of the Tet repressor, which resulted in acceptable values for the predicted lifetimes.