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Abstract
Peripheral events in olfaction involve odorant binding proteins (OBPs) whose role in the recognition of different volatile chemicals is yet unclear. Here we report on the sensitive and quantitative measurement of the weak interactions associated with neutral enantiomers differentially binding to OBPs immobilized through a self-assembled monolayer to the gate of an organic bio-electronic transistor. The transduction is remarkably sensitive as the transistor output current is governed by the small capacitance of the protein layer undergoing minute changes as the ligand–protein complex is formed. Accurate determination of the free-energy balances and of the capacitance changes associated with the binding process allows derivation of the free-energy components as well as of the occurrence of conformational events associated with OBP ligand binding. Capacitance-modulated transistors open a new pathway for the study of ultra-weak molecular interactions in surface-bound protein–ligand complexes through an approach that combines bio-chemical and electronic thermodynamic parameters.
Highlights
Peripheral events in olfaction involve odorant binding proteins (OBPs) whose role in the recognition of different volatile chemicals is yet unclear
With this approach we achieve the sensitive evaluation of energies as low as 1.1±0.5 kJ mol À 1, associated with neutral enantiomers differentially binding to a porcine OBPs (pOBPs) immobilized through a self-assembled monolayer (SAM)
All the dissociation constants evaluated with the water-gated organic field-effect transistor (WGOFET)
Summary
Peripheral events in olfaction involve odorant binding proteins (OBPs) whose role in the recognition of different volatile chemicals is yet unclear. We report on the sensitive and quantitative measurement of the weak interactions associated with neutral enantiomers differentially binding to OBPs immobilized through a self-assembled monolayer to the gate of an organic bio-electronic transistor. As m is equal to m þ nFV (m 1⁄4 chemical potential, F 1⁄4 Faraday’s constant, n 1⁄4 moles of charges and V 1⁄4 electrostatic potential), it is associated with strong long-range coulomb interactions (10–100 kJ mol À 1) This is why FETs generally provide sensitive detection in reactions that involve charged species, but are less successful for quantitative detection of neutral species[30]. This article reports on the binding of (S)-( þ )- and (R)-( À )carvone enantiomers to a pOBP-mutant-F88W, detected by means of a WGOFET With this approach we achieve the sensitive evaluation of energies as low as 1.1±0.5 kJ mol À 1, associated with neutral enantiomers differentially binding to a pOBP immobilized through a self-assembled monolayer (SAM). Analysis of the free-energy balance and of the degree of capacitance decreases, provides strong support for the hypothesis that on S-( þ )-carvone ligand binding the pOBP undergoes a conformational change that is not seen with the R-( À ) enantiomer
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