Toward an understanding of the retinal chromophore in rhodopsin mimics

J Phys Chem B. 2013 Sep 5;117(35):10053-70. doi: 10.1021/jp305935t. Epub 2013 Aug 26.

Abstract

Recently, a rhodopsin protein mimic was constructed by combining mutants of the cellular retinoic acid binding protein II (CRABPII) with an all-trans retinal chromophore. Here, we present a combined computational quantum mechanics/molecular mechanics (QM/MM) and experimental ultrafast kinetic study of CRABPII. We employ the QM/MM models to study the absorption (λ(a)max), fluorescence (λ(f)max), and reactivity of a CRABPII triple mutant incorporating the all-trans protonated chromophore (PSB-KLE-CRABPII). We also study the spectroscopy of the same mutant incorporating the unprotonated chromophore and of another double mutant incorporating the neutral unbound retinal molecule held inside the pocket. Finally, for PSB-KLE-CRABPII, stationary fluorescence spectroscopy and ultrafast transient absorption spectroscopy resolved two different evolving excited state populations which were computationally assigned to distinct locally excited and charge-transfer species. This last species is shown to evolve along reaction paths describing a facile isomerization of the biologically relevant 11-cis and 13-cis double bonds. This work represents a first exploratory attempt to model and study these artificial protein systems. It also indicates directions for improving the QM/MM models so that they could be more effectively used to assist the bottom-up design of genetically encodable probes and actuators employing the retinal chromophore.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Biomimetic Materials / chemistry*
  • Biomimetic Materials / metabolism
  • Isomerism
  • Kinetics
  • Molecular Dynamics Simulation
  • Mutation
  • Protein Structure, Tertiary
  • Quantum Theory
  • Receptors, Retinoic Acid / chemistry
  • Receptors, Retinoic Acid / genetics
  • Receptors, Retinoic Acid / metabolism
  • Retinaldehyde / chemistry*
  • Rhodopsin / chemistry*
  • Rhodopsin / metabolism
  • Spectrometry, Fluorescence
  • Static Electricity

Substances

  • Receptors, Retinoic Acid
  • retinoic acid binding protein II, cellular
  • Rhodopsin
  • Retinaldehyde