USING 7-AZATRYPTOPHAN TO PROBE SMALL MOLECULE-PROTEIN INTERACTIONS ON THE PICOSECOND TIME SCALE - THE COMPLEX OF AVIDIN AND BIOTINYLATED 7-AZATRYPTOPHAN

摘要

The utility of 7-azatryptophan as an alternative to tryptophan for optically probing protein structure and dynamics is demonstrated by investigating the complex of egg-white avidin and biotinylated 7-azatryptophan. We report the synthesis of biotinylated 7-azatryptophan and optical measurements of its complex with avidin. Although there are four biotin binding sites, the emission from the 7-azatryptophan tagged to biotin decays by a single exponential, whereas the tryptophyl emission from avidin requires two exponentials in order to be adequately fit. Fluorescence depolarization measurements of the complex probed by emission from 7-azatryptophan reveal both rapid (similar to 80 ps) and much longer-lived decay. The former component is attributable to the local motion of the probe with respect to the protein; the latter component represents overall protein tumbling. In addition, energy transfer from tryptophan to 7-azatryptophan and a blue-shift in the spectrum of biotinylated 7-azatryptophan are observed upon formation of the complex. Modified strategies of effecting optical selectivity are also discussed. [References: 41]