The fluorescence intensity decay of variant-3 scorpion neurotoxin has an average lifetime of 510 picoseconds. The consensus of least squares, maximum likelihood, Pade-Laplace, and distributional analyses of this decay is that more than 90% of the initial intensity comes from short lifetime components with lifetimes in the range 0.05 to 0.5 nanoseconds and the remaining small fraction of initial intensity is essentially one component decaying with an average lifetime of about 2 nanoseconds. Both adiabatic mapping and combined thermodynamic perturbation and umbrella sampling simulations reveal the presence of two tryptophan-47 rotational isomers. One of the isomers corresponds closely to the crystallographic structure and the second is a new rotational isomer that is separated from the first by a rotation angle of about 220 degrees and an activation barrier of about 10 kcal/mole. We propose that the short lifetime components correspond to conformers with tryptophan-47 approximately in the crystallographic orientation and the long lifetime component is the new rotational isomer identified in the simulations.

Date Published: 1 May 1990
PDF: 8 pages
Proc. SPIE 1204, Time-Resolved Laser Spectroscopy in Biochemistry II, (1 May 1990); doi: 10.1117/12.17691

Published in SPIE Proceedings Vol. 1204:
Time-Resolved Laser Spectroscopy in Biochemistry II
Joseph R. Lakowicz, Editor(s)