Deciphering the Spectral Tuning Mechanism in Proteorhodopsin: The Dominant Role of Electrostatics Instead of Chromophore Geometry

Jonathan R. Church, Gil S. Amoyal, Veniamin A. Borin, Suliman Adam, Jógvan Magnus Haugaard Olsen, Igor Schapiro*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Proteorhodopsin (PR) is a photoactive proton pump found in marine bacteria. There are two phenotypes of PR exhibiting an environmental adaptation to the ocean's depth which tunes their maximum absorption: blue-absorbing proteorhodopsin (BPR) and green-absorbing proteorhodopsin (GPR). This blue/green color-shift is controlled by a glutamine to leucine substitution at position 105 which accounts for a 20 nm shift. Typically, spectral tuning in rhodopsins is rationalized by the external point charge model but the Q105L mutation is charge neutral. To study this tuning mechanism, we employed the hybrid QM/MM method with sampling from molecular dynamics. Our results reveal that the positive partial charge of glutamine near the C14−C15 bond of retinal shortens the effective conjugation length of the chromophore compared to the leucine residue. The derived mechanism can be applied to explain the color regulation in other retinal proteins and can serve as a guideline for rational design of spectral shifts.

Original languageAmerican English
Article numbere202200139
JournalChemistry - A European Journal
Issue number28
Early online date20 Mar 2022
StatePublished - 16 May 2022

Bibliographical note

Funding Information:
I.S. thanks the DFG Collaborative Research Center 1078, project C6 for support. I.S. gratefully acknowledges funding by the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant No. 678169 “PhotoMutant”). J.R.C thanks the Zuckerman STEM Leadership Program for their support. S.A. thanks the Minerva Stiftung for a post‐doctoral fellowship within the framework of the Minerva Fellowship Program. J.M.H.O. thanks VILLUM FONDEN for financial support (grant no. 29478).

Publisher Copyright:
© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.


  • QM/MM
  • proteorhodopsin
  • retinal
  • rhodopsin
  • spectral tuning


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