TIME-RESOLVED FLUORESCENCE PROPERTIES OF PHENYLALANINE IN DIFFERENT ENVIRONMENTS - COMPARISON WITH MOLECULAR-DYNAMICS SIMULATION

Time resolved fluorescence of the phenylalanine residue (Phe) alone an d included in the transmembrane domain (TMD) sequences of the epiderma l growth factor receptor (EGFR) and ErbB-2 was studied using the synch rotron radiation source of light, and compared to molecular dynamics ( MD) simulations. The fluorescence intensity decay is strongly sensitiv e to the environment. A mono-exponential decay was obtained for Phe am ino acid alone in two different solvents and for Phe included in EGFR transmembrane sequence, with fluorescence lifetime values varying from 1.7 ns (EGFR) to 7.4 ns (Phe dissolved in water). In ErbB-2 transmemb rane sequence three lifetimes were detected. The relative amplitude of the shortest one (0.14 ns) is smaller than 10%, whereas the others (0 .6 and 2.2 ns) are almost equally represented. They have been attribut ed to different rotamers exchanging slowly. This interpretation is sup ported by MD simulations which evidence transitions in time series of the chi(1) dihedral angle of Phe observed in the case of ErbB-2. The a nisotropy decays are similar for both peptides and indicate the presen ce of a correlation time in the nanosecond range (1-4 ns) and the prob able existence of a very fast one (< 0.05 ns). Autocorrelation functio ns computed from MD simulations corroborate these results. (C) 1998 El sevier Science B.V. All rights reserved.