Computer-Aided Rational Construction of Mediated Bioelectrocatalysis with π-Conjugated (Hetero)cyclic Molecules: Toward Promoted Distant Electron Tunneling and Improved Biosensing.

Abstract

Highly π-conjugated (hetero)cyclic molecules having delocalized orbitals and tunable charge mobilities are attractive redox relays for mediated bioelectrocatalysis in manifold applications. As rigid molecules, their dynamics within the soft but confined intraprotein space becomes the crucial determinant of the enzyme-mediator electron-tunneling efficiency. However, it is rarely investigated in designing the mediated interface with a particular biocatalyst (e.g., oxidoreductase), which remains an empirical but try-and-error process. Herein, we present the computer-aided exploration of interactions between a flavin-containing reductive synthase and structurally diverse π-extended (hetero)cyclic mediators to realize reversed bioelectrocatalytic oxidation at low overpotentials. Compared to ring-fused systems with unbroken molecular planarity, heteroatom-bridged cyclic, and rotatable conjugated structures (e.g., indophenols) can experience unusually large dynamic torsion under biased forces of hydrogen bonding with enzyme residues. This behavior led to fast intraprotein reorientation (<50 ps) that shortened the electron-tunneling distance from 12 to 9 Å. Meanwhile, the lowest unoccupied molecular orbital level upon molecular torsion was decreased by 0.5 eV to further promote electron abstraction from the reduced flavin cofactor. An efficient distant electron tunneling also obviated mediator transport through the substrate channel, thus avoiding competitive inhibition on enzyme kinetics to broaden the operating concentration range. The resulting bioelectrocatalytic interface enables low-potential biosensing of glutamate with improved selectivity. Our finding provides new structural insights into constructing efficient long-range heterogeneous charge transport with biomacromolecular catalysts.