TY - JOUR
T1 - Toward an understanding of the retinal chromophore in rhodopsin mimics
AU - Huntress, Mark M.
AU - Gozem, Samer
AU - Malley, Konstantin R.
AU - Jailaubekov, Askat E.
AU - Vasileiou, Chrysoula
AU - Vengris, Mikas
AU - Geiger, James H.
AU - Borhan, Babak
AU - Schapiro, Igor
AU - Larsen, Delmar S.
AU - Olivucci, Massimo
PY - 2013/9/5
Y1 - 2013/9/5
N2 - 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 (λamax), fluorescence (λf 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.
AB - 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 (λamax), fluorescence (λf 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.
UR - https://www.scopus.com/pages/publications/84883694932
U2 - 10.1021/jp305935t
DO - 10.1021/jp305935t
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C2 - 23971945
AN - SCOPUS:84883694932
SN - 1520-6106
VL - 117
SP - 10053
EP - 10070
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 35
ER -