Unravelling the Turn-On Fluorescence Mechanism of a Fluorescein-Based Probe in GABAA Receptors

Nadja K Singer; Pedro A Sánchez-Murcia; Margot Ernst; Leticia González

doi:10.1002/anie.202205198

Unravelling the Turn-On Fluorescence Mechanism of a Fluorescein-Based Probe in GABA_A Receptors

Angew Chem Int Ed Engl. 2022 Jul 25;61(30):e202205198. doi: 10.1002/anie.202205198. Epub 2022 May 12.

Authors

Nadja K Singer^{1

2}, Pedro A Sánchez-Murcia^{1

3}, Margot Ernst⁴, Leticia González^{1

5}

Affiliations

¹ Institute of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Str. 17, 1090, Vienna, Austria.
² Vienna Doctoral School in Chemistry (DoSChem), University of Vienna, Währinger Str. 42, 1090, Vienna, Austria.
³ Present address: Division of Physiological Chemistry, Otto-Loewi Research Center, Medical University of Graz, Neue Stiftingtalstr. 6/III, 8010, Graz, Austria.
⁴ Department of Molecular Neurosciences (Center for Brain Research), Medical University of Vienna, Spitalgasse 4, 1090, Vienna, Austria.
⁵ Vienna Research Platform on Accelerating Photoreaction Discovery, University of Vienna, Währinger Str. 17, 1090, Vienna, Austria.

Abstract

GABA_A (γ-aminobutyric acid type A) receptors are ligand-gated ion channels mediating fast inhibitory transmission in the mammalian brain. Here we report the molecular and electronic mechanism governing the turn-on emission of a fluorescein-based imaging probe able to target the human GABA_A receptor. Multiscale calculations evidence a drastic conformational change of the probe from folded in solution to extended upon binding to the receptor. Intramolecular ππ-stacking interactions present in the folded probe are responsible for quenching fluorescence in solution. In contrast, unfolding within the GABA_A receptor changes the nature of the bright excited state triggering emission. Remarkably, this turn-on effect only manifests for the dianionic prototropic form of the imaging probe, which is found to be the strongest binder to the GABA_A receptor. This study is expected to assist the design of new photoactivatable screening tools for allosteric modulators of the GABA_A receptor.

Keywords: Charge Transfer States; Fluorescent Probe; GABA-a Receptor; Gabazine; QM/MM.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Fluorescein
Fluorescence
Humans
Mammals / metabolism
Receptors, GABA-A* / chemistry
Receptors, GABA-A* / metabolism
gamma-Aminobutyric Acid* / pharmacology

Substances

Receptors, GABA-A
gamma-Aminobutyric Acid
Fluorescein