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Photoactive Yellow Protein Chromophore Photoisomerizes around a Single Bond if the Double Bond Is Locked.

ABSTRACT: Photoactivation in the Photoactive Yellow Protein, a bacterial blue-light photoreceptor, proceeds via photoisomerization of the double C?C bond in the covalently attached chromophore. Quantum chemistry calculations, however, have suggested that in addition to double-bond photoisomerization, the isolated chromophore and many of its analogues can isomerize around a single C-C bond as well. Whereas double-bond photoisomerization has been observed with X-ray crystallography, experimental evidence of single-bond photoisomerization is currently lacking. Therefore, we have synthesized a chromophore analogue, in which the formal double bond is covalently locked in a cyclopentenone ring, and carried out transient absorption spectroscopy experiments in combination with nonadiabatic molecular dynamics simulations to reveal that the locked chromophore isomerizes around the single bond upon photoactivation. Our work thus provides experimental evidence of single-bond photoisomerization in a photoactive yellow protein chromophore analogue and suggests that photoisomerization is not restricted to the double bonds in conjugated systems. This insight may be useful for designing light-driven molecular switches or motors.

SUBMITTER: Mustalahti S

PROVIDER: S-EPMC7145348 | biostudies-literature | 2020 Mar

REPOSITORIES: biostudies-literature

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Photoactive Yellow Protein Chromophore Photoisomerizes around a Single Bond if the Double Bond Is Locked.

Mustalahti Satu S Morozov Dmitry D Luk Hoi Ling HL Pallerla Rajanish R RR Myllyperkiö Pasi P Pettersson Mika M Pihko Petri M PM Groenhof Gerrit G

The journal of physical chemistry letters 20200304 6

Photoactivation in the Photoactive Yellow Protein, a bacterial blue-light photoreceptor, proceeds via photoisomerization of the double C═C bond in the covalently attached chromophore. Quantum chemistry calculations, however, have suggested that in addition to double-bond photoisomerization, the isolated chromophore and many of its analogues can isomerize around a single C-C bond as well. Whereas double-bond photoisomerization has been observed with X-ray crystallography, experimental evidence of ...[more]

PMID: 32109070

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Project description:We have performed ab initio CASSCF, CASPT2, and EOM-CCSD calculations on doubly deprotonated p-coumaric acid (pCA(2-)), the chromophore precursor of the photoactive yellow protein. The results of the calculations demonstrate that pCA(2-) can undergo only photoisomerization of the double bond. In contrast, the chromophore derivative with the acid replaced by a ketone (p-hydroxybenzylidene acetone, pCK(-)) undergoes both single- and double-bond photoisomerization, with the single-bond relaxation channel more favorable than the double-bond channel. The substitution alters the nature of the first excited states and the associated potential energy landscape. The calculations show that the electronic nature of the first two (?,?*) excited states are interchanged in vacuo due to the substitution. In pCK(-), the first excited state is a charge-transfer (CT ?,?*) state, in which the negative charge has migrated from the phenolate ring onto the alkene tail of the chromophore, whereas the locally excited (LE ?,?*) state, in which the excitation involves the orbitals on the phenol ring, lies higher in energy and is the fourth excited state. In pCA(2-), the CT state is higher in energy due the presence of a negative charge on the tail of the chromophore, and the first excited state is the LE state. In isolated pCA(2-), there is a 68 kJ/mol barrier for double-bond photoisomerization on the potential energy surface of this LE state. In water, however, hydrogen bonding with water molecules reduces this barrier to 9 kJ/mol. The barrier separates the local trans minimum near the Franck-Condon region from the global minimum on the excited-state potential energy surface. The lowest energy conical intersection was located near this minimum. In contrast to pCK(-), single-bond isomerization is highly unfavorable both in the LE and CT states of pCA(2-). These results demonstrate that pCA(2-) can only decay efficiently in water and exclusively by double-bond photoisomerization. These findings provide a rationale for the experimental observations that pCA(2-) has both a longer excited-state lifetime and a higher isomerization quantum yield than pCK(-).

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Photoactive Yellow Protein Chromophore Photoisomerizes around a Single Bond if the Double Bond Is Locked.

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Photoactive Yellow Protein Chromophore Photoisomerizes around a Single Bond if the Double Bond Is Locked.

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