FLUORESCENCE AND MONTE-CARLO CONFORMATIONAL STUDIES OF THE (1-15) GALANIN AMIDE FRAGMENT

Galanin (GAL) is a 29 amino acid C-terminally aminated linear neuropep tide showing diverse biological activities. The N-terminal (1-15)GAL-N H2 fragment was shown to have a very high affinity to the galanin rece ptor. In this work we describe the results of a combined fluorescence and Monte Carlo studies, the latter carried out using the ECEPP/3 forc e field with and without including hydration, on the (1-15)GAL-NH2 fra gment. Using the time-domain technique we measured fluorescence decay times of the tyrosine residue in position 9. Based on the Forster ener gy transfer theory we calculated the distance and distance distributio n between the Trp(2) (acceptor) and Tyr(9) (donor) aromatic side chain s. The distance obtained was about 10.5 Angstrom and half-width, hw, o f the distance distribution was 5.6 Angstrom. This results were found to be in good agreement with the chromophore distances calculated for the low-energy solution confirmations obtained in Monte Carlo simulati ons. All the low-energy conformations obtained in the absence of water were almost all-helical with the exception of a few C-terminal residu es. In contrast, none of the low-energy solution conformations contain ed any significant amount of secondary structure. These findings are i n agreement with the results of earlier CD and NMR conformational stud ies of galanin in water and non-aqueous solvents. On the other hand, t he conformations obtained in the presence of water turned out to be la rgely compact in the N-terminal hydrophobic part. This explains the re latively short distance between chromophores and narrow distance distr ibution obtained in fluorescence measurements.