Ultrafast electron transfer in the complex between fluorescein and a cognate engineered lipocalin protein, a so-called anticalin

Biochemistry
M GötzM E Michel-Beyerle

Abstract

Anticalins are a novel class of engineered ligand-binding proteins with tailored specificities derived from the lipocalin scaffold. The anticalin FluA complexes fluorescein as ligand with high affinity, and it effects almost complete quenching of its steady-state fluorescence. To study the underlying mechanism, we have applied femtosecond absorption spectroscopy, which revealed excited-state electron transfer within the FluA*Fl complex to be responsible for the strong fluorescence quenching. On the basis of a comparison of redox potentials, either tryptophan or tyrosine may serve as electron donor to the bound fluorescein group in its excited singlet state, thus forming the fluorescein trianion radical within 400 fs. The almost monoexponential rate points to a single, well-defined binding site, and its temperature independence suggests an (almost) activationless process. Applying conventional electron transfer theory to the ultrafast forward and slower back-rates, the resulting electronic interaction is rather large, with approximately 140 cm(-1) for tyrosine, which would be consistent with a coplanar arrangement of both aromatic moieties within van der Waals distance. The weak residual steady-state fluorescence originates from...Continue Reading

References

Nov 4, 2000·Biochimica Et Biophysica Acta·A Skerra
Sep 1, 1996·Journal of Fluorescence·N Klonis, W H Sawyer

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Citations

May 8, 2010·Journal of the American Chemical Society·Huimin ChenWatt W Webb
Oct 27, 2010·Physical Chemistry Chemical Physics : PCCP·Mijeong KangHan Young Woo
Apr 9, 2008·Proceedings of the National Academy of Sciences of the United States of America·Johannes WiedersichJosef Friedrich
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