Point Mutation of Anabaena Sensory Rhodopsin Enhances Ground-State Hydrogen Out-of-Plane Wag Raman Activity

Abstract

The interaction between the retinal protonated Schiff base (RPSB) and surrounding protein residues inside the retinal pocket is believed to play a major role in the ultrafast isomerization of the former. Coherent time-resolved vibrational spectroscopic techniques are applied to reveal the effect of changes in the protein architecture by point mutations (V112N and L83Q) close to the RPSB in Anabaena sensory rhodopsin (ASR). Our study reveals that such point mutations have a minor effect on the low-frequency (<400 cm–1) torsional modes but dramatically influence the ground-state vibrational Raman activity of the C14–H out-of-plane (HOOP) wag mode (800–820 cm–1). In mutated ASR, the increase of HOOP Raman activity in the ground state is experimentally observed for the all-trans RPSB, which has shorter excited-state lifetime than in wild-type ASR. This indicates that predistortion of the RPSB inside the mutated retinal pocket is a major factor in the acceleration of the isomerization rate.

Excited State Structure Correlates with Efficient Photoconversion in Unidirectional Motors

“…While not previously reported in motor molecules, such low frequency modes have been seen in other isomerization reactions, in phytochromes and rhodopsins, for example. [26][27][28] In those cases HOOP activity was an important coordinate, and we note that the calculated ground state pyramidalization mode for the motor molecules also includes significant HOOP displacements (Figure S7). In contrast, in the −OMe derivative the 720 cm -1 mode is essentially absent and an intense 1580 cm -1 mode is retained, suggesting an excited state geometry where the ethylene axle with sp 2 character carbon (labeled as sp 2 dark state, Ssp2) is favored, and there is little displacement along the pyramidalization coordinate.…”

Sub-picosecond C=C bond photo-isomerization: evidence for the role of excited state mixing

“…This allows us to generalize the central role of the intramolecular steric effect and pre-twist at controlling the PES topography via the fine tuning of the S 1 -S 2 state mixing in these retinal-inspired compounds. As reviewed in chapter II&III, the same effect of a pre-twist of the chromophore is operative in 13C/ASR in reducing the excited state barrier [111]. A major outcome of our latest study [20], is that while the intramolecular steric hindrance and related S 1 -S 2 state mixing controls the photoreaction dynamics, we observe no correlation between the IQY -in the range 15 % to 35 % for all IP compounds investigated -and observables such as excited state life time, vibrational coherence, absorption wavelengths or degree of pre-twisting.…”

“…Preliminary results point to a bi-exponential decay from S 1 , modulated by its pH-dependent interaction with S 2 . Further upcoming developments relate to computing the excited state vibrational spectra of the rPSB, in relation with the very informative femtosecond data [91,111], and a possible inclusion of the dynamic polarisation of the nearest neighbour residues [15,74,75]. Unlike the here reported transient spectroscopies, ultrafast X-ray diffraction has the potential of revealing the detailed dynamic structural and electronic changes of the rPSB and its nearest environment, provided these experiments be carried out under single photon excitation conditions [63,72,73,126].…”

“…were studied by femtosecond DFWM and IVS in the DA and LA states [111], under exactly the same conditions as the ones used in the above TA experiments. It was found that mutations lead to an enhanced HOOP mode activity in the AT ground state of L83Q and V112N indicating a pre-distorsion of the chromophore either around the active C13=C14 bond or neighbouring C14−C15 bond of the ground state compared to the AT-isomer in the wt-ASR [111]. Additionally, the high frequency vibrations related to C-C single bond or C=C double bond stretch, as well as CH 3 rock modes change consistently with a reduced conjugation length, induced by the pre-distortion.…”

Raman Scattering: From Structural Biology to Medical Applications

“…In the recent study, the Raman measurements showed that the longer dynamics that were observed for AT ASR may result both from a barrier in the excited state and the lack of a pre-distortion (compared to 13C isomer) in the ground state [320]. The increase of ground-state C14−HOOP Raman activity of AT and 13C-isomers caused by point mutation showed that localized change in electrostatic interaction mutation might induce a subtle distortion of retinal geometry, which might lead to an accelerated isomerization kinetics [321].…”