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

Abstract

GABAA (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 GABAA 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 GABAA 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 GABAA receptor. This study is expected to assist the design of new photoactivatable screening tools for allosteric modulators of the GABAA receptor.

Highly Selective and Rapid “Turn-On” Fluorogenic Chemosensor for Detection of Salicylic Acid in Plants and Food Samples

“…Moreover, the N , N -diethyl group of the probe Rh6G-Py could form a hydrogen bond (the distance of 2.54 Å) with the COOH of SA. More importantly, the binding energy ( E b ) and enthalpy (Δ H ) of Rh6G-Py + SA were −19.1 and −16.4 kcal/mol, which were higher than those of Rh6G-Th + SA ( E b = −18.7 kcal/mol; Δ H = −12.4 kcal/mol) and Rh6G-BT + SA ( E b = −6.9 kcal/mol; Δ H = −5.0 kcal/mol), indicating that Rh6G-Py is more accessible to interact with SA than Rh6G-Th and Rh6G-BT , Thus, a suitable bonding model may endow probes the good response capability toward SA. Accordingly, the possible reaction mechanism between probe Rh6G-Py and SA was proposed, as shown in Scheme .…”

“…These values were relatively lower than the Rh6G-Py + SA system (−19.1 kcal/mol), indicating that Rh6G-Py + SA was more stable than Rh6G-Py + SA analogues because the functional groups (–OH and –COOH) of SA could interact synergistically with a nitrogen atom and hydrogen atoms of Rh6G-Py to form various hydrogen bonds (see Figure ). , Furthermore, the enthalpy (Δ H ) is a crucial indicator in response to the complex’s stability. For instance, the probe Rh6G-Py + SA system afforded the highest enthalpy (Δ H = −16.4 kcal/mol).…”

“…Moreover, the N,N-diethyl group of the probe Rh6G-Py could form a hydrogen bond (the distance of 2.54 Å) with the COOH of SA. More importantly, the binding energy (E b ) Rh6G-Py is more accessible to interact with SA than Rh6G-Th and Rh6G-BT 34,35 Thus, a suitable bonding model may endow probes the good response capability toward SA. Accordingly, the possible reaction mechanism between probe Rh6G-Py and SA was proposed, as shown in Scheme 2.…”

Molecular Design Strategy of Protein Isoform-Specific Fluorescent Probes by Considering Molecule in Its Entirety

“…In fact, MD was previously used to define the recognition mechanism of the fluorescent probe for GABA1. 32 Hence, a molecular design strategy for isoform-specific fluorescent probes could be put forward through a comprehensive consideration of the relationship between the recognition performance and the simulated structure of the protein−probe complex (Figure 1). 33 Hex plays essential roles in vital metabolic processes such as chitin degradation and human autoimmune diseases, and lack of HexA and HexB could lead to several diseases.…”

“…The use of MD can simulate a more accurate protein–probe complex structure. In fact, MD was previously used to define the recognition mechanism of the fluorescent probe for GABA1 . Hence, a molecular design strategy for isoform-specific fluorescent probes could be put forward through a comprehensive consideration of the relationship between the recognition performance and the simulated structure of the protein–probe complex (Figure ).…”