Ultrafast electron transfer in the recognition of different DNA sequences by a DNA-binding protein with different dynamical conformations.

Ultrafast electron transfer (ET) phenomenon in protein and protein-DNA complex is very much crucial and often leads to the regulation of various kinds of redox reactions in biological system. Although, the conformation of the protein in protein-DNA complex is concluded to play the key role in the ET process, till date very little evidences exist in the literature. λ-repressor-operator DNA interaction, particularly O(R)1 and O(R)2, is a key component of the λ-genetic switch and is a model system for understanding the chemical principles of the conformation-dependent ET reaction, governed by differential protein dynamics upon binding with different DNA target sequences. Here, we have explored the photoinduced electron transfer from the tryptophan moieties of the protein λ-repressor to two operators DNA of different sequences (O(R)1 and O(R)2) using picosecond-resolved fluorescence spectroscopy. The enhanced flexibility and different conformation of the C-terminal domain of the repressor upon complexation with O(R)1 DNA compared to O(R)2 DNA are found to have pronounced effect on the rate of ET. We have also observed the ET phenomenon from a dansyl chromophore, bound to the lysine residue, distal from the DNA-binding domain of the protein to the operator DNA with a specific excitation at 299 nm wavelength. The altered ET dynamics as a consequence of differential protein conformation upon specific DNA sequence recognition may have tremendous biological implications.