Proton transfer and conformational changes along the hydrogen bond network in heliorhodopsin

Heliorhodopsin releases a proton from the Schiff base during the L-state to M-state transition but not toward the protein bulk surface. Here we investigate proton transfer and induced structural changes along the H-bond network in heliorhodopsin using a quantum mechanical/molecular mechanical approach and molecular dynamics simulations. Light-induced proton transfer could occur from the Schiff base toward Glu107, reorienting Ser76, followed by subsequent proton transfer toward His80. His80 protonation induces the reorientation of Trp246 on the extracellular surface, originating from the electrostatic interaction that propagates along the transmembrane H-bond network [His80 horizontal ellipsis His23 horizontal ellipsis H2O[H23/Q26] horizontal ellipsis Gln26 horizontal ellipsis Trp246] over a distance of 15 & ANGS;. Furthermore, it induces structural fluctuation on the intracellular side in the H-bond network [His80 horizontal ellipsis Asn16 horizontal ellipsis Tyr92 horizontal ellipsis Glu230 horizontal ellipsis Arg104 horizontal ellipsis Glu149], opening the inner cavity at the Tyr92 moiety. These may be a basis of how light-induced proton transfer causes conformational changes during the M-state to O-state transition.

Automated summary

This study investigates proton transfer and induced structural changes in heliorhodopsin using quantum mechanical/molecular mechanical approach and molecular dynamics simulations. The results suggest that light-induced proton transfer occurs from the Schiff base to Glu107, followed by reorientation of Ser76 and subsequent proton transfer to His80. Protonation of His80 induces reorientation of Trp246 on the extracellular surface and structural fluctuation on the intracellular side.