Cooperative long range protein-protein dynamics in Purple Membrane

TL;DR

This study provides experimental evidence of long-range protein-protein interactions in purple membrane, quantifies interprotein dynamics via phonon spectra, and identifies intraprotein excitations, advancing understanding of membrane protein interactions.

Contribution

First to measure and model long-range protein-protein interactions in purple membrane using inelastic neutron scattering.

Findings

Phonon energies around 1 meV were observed.

Effective spring constant for protein interactions is 53 N/m.

Optical-like excitations at 0.45 meV were identified.

Abstract

We present experimental evidence for a long-range protein-protein interaction in purple membrane (PM). The interprotein dynamics were quantified by measuring the spectrum of the acoustic phonons in the 2D bacteriorhodopsin (BR) protein lattice using inelastic neutron scattering. Phonon energies of about 1 meV were determined. The data are compared to an analytical model, and the effective spring constant for the interaction between neighboring protein trimers are determined to be k=53 N/m. Additional, optical-like excitations at 0.45 meV were found and assigned to intraprotein dynamics between neighboring BR monomers.