Energy Transport and its Function in Heptahelical Transmembrane Proteins

TL;DR

This study investigates vibrational energy transport in GPCRs and bacteriorhodopsin, revealing different energy dissipation strategies and structural influences on energy flow in active and inactive states.

Contribution

It applies a master equation approach to compare energy transport mechanisms across structurally similar GPCRs and bacteriorhodopsin.

Findings

bR quickly dissipates energy via TM7 helix

Rho shows poor energy dissipation, risking overheating

B2AR's energy network changes with activation state

Abstract

Photoproteins such as bacteriorhodopsin (bR) and rhodopsin (Rho) need to effectively dissipate photoinduced excess energy to prevent their damage. Another well-studied G protein-coupled receptor (GPCR) containing 7 transmembrane (TM) helices is the B2 adrenergic receptor (B2AR), for which energy dissipation paths have been linked with allosteric communication. To study the vibrational energy transport in the active and inactive states of these GPCRs, a master equation approach [J. Chem. Phys. 152, 045103 (2020)] is employed, which uses scaling rules that allow to calculate energy transport rates solely based on the protein structure. Despite their structural similarities, the three GPCRs reveal quite different strategies to redistribute excess energy. While bR quickly removes the energy using the TM7 helix as a "lightning rod", Rho exhibits a rather poor energy dissipation, which might eventually require the hydrolysis of the Schiff base between the protein and the retinal chromophore to prevent overheating. Heating the ligand adrenaline of B2AR, the resulting energy transport network of the protein is found to change significantly upon switching from the active to the inactive state. While the energy flow may highlight aspects of the interresidue couplings of B2AR, it seems not particularly suited to explain allosteric phenomena.