Early molecular events in the photoactive yellow protein: role of the chromophore photophysics.
We report a comparative study of the isomerization reaction in native and denatured photoactive yellow protein (PYP) and in various chromophore analogues in their trans deprotonated form. The excited-state relaxation dynamics was followed by subpicosecond transient absorption and gain spectroscopy. The free p-hydroxycinnamate (pCA(2-)) and its amide analogue (pCM(-)) are found to display a quite different transient spectroscopy from that of PYP. The excited-state deactivation leads to the formation of the ground-state cis isomer without any detectable intermediate with a mechanism comparable to trans-stilbene photoisomerization. On the contrary, the early stage of the excited-state deactivation of the free thiophenyl-p-hydroxycinnamate (pCT(-)) and of the denatured PYP is similar to that of the native protein. It involves the formation of an intermediate absorbing in the spectral region located between the bleaching and gain bands in less than 2 ps. However, in these two cases, the formation of the cis isomer has not been proved yet. This difference with pCA(-) and pCM(-) might result from the fact that, in the thioester substituted chromophore, simultaneous population of two quasi-degenerate excited states occurs upon excitation. This comparative study highlights the determining role of the chromophore structure and of its intrinsic properties in the primary molecular events in native PYP.
Departement de Chimie, Ecole Normale Superieure (UMR CNRS 8640 PASTEUR), 24 rue Lhomond, 75231 Paris Cedex 05, France.
Pascale
P
Changenet-Barret
Agathe
A
Espagne
Sandrine
S
Charier
Jean-Bernard
JB
Baudin
Ludovic
L
Jullien
Pascal
P
Plaza
Klaas J
KJ
Hellingwerf
Monique M
MM
Martin
D001426:Bacterial Proteins / Q000737:chemistry*; D004583:Electrons; D007536:Isomerism; D010777:Photochemistry; D020283:Photoreceptors, Microbial / Q000737:chemistry*; D011489:Protein Denaturation; D013057:Spectrum Analysis
D001426:Bacterial Proteins; D020283:Photoreceptors, Microbial; C050162:photoactive yellow protein, Bacteria