Real-Time Tracking of Phytochrome’s Orientational Changes During Pr Photoisomerization

Abstract

Photoisomerization of a protein bound chromophore is the basis of the light sensing and signaling responses of many photoreceptors. Z-to-E photoisomerization of the Pr Cph1Δ2 phytochrome has been investigated by polarization resolved femtosecond visible pump-infrared probe spectroscopy, which yields structural information on the Pr excited (Pr*), Pr ground, and lumi-R product states. By exhaustive search analysis, two photoreaction time constants of (4.7 ± 1.4) and (30 ± 5) ps were found. Ring D orientational change in the electronic excited state to the transition state (90° twist) has been followed in real-time. Rotation of ring D takes place in the electronically excited state with a time constant of 30 ± 5 ps. The photoisomerization is best explained by a single rotation around C(15)═C(16) methine bridge in the Pr* state and a diffusive interaction with its protein surrounding.

Ultrafast E to Z photoisomerization dynamics of the Cph1 phytochrome

“…Ignoring FC evolution, the 15E P fr → 15Z P r excited-state quenching dynamics of Cph1 are considerably faster than those of the primary 15Z P r → 15E P fr forward excited-state dynamics (multi-exponential excited-state decay of ~3, 30, and ~150 ps) [9,15,16,18,33]. Faster reverse E→Z excited-state dynamics are also observed in other phytochrome and cyanobacteriochrome systems [10–13,26,27].…”

Spectroscopic Investigation on the Primary Photoreaction of Bathy Phytochrome Agp2‐Pr of Agrobacterium fabrum: Isomerization in a pH‐dependent H‐bond Network

“…[13] Upon red-light absorption the Pr chromophoreu ndergoes ar apid Z/E isomerization at the C15 methine bridge, finally resultingi naZZEssa stereochemistry of the Pfr chromophore. [14][15][16][17][18][19] Both primary light induced reactions involve several excited-state intermediates and evolve on ap icosecond time scale, typically with a" slow" Pr reaction (30-100 ps or longer) [20][21][22][23][24][25][26][27][28][29][30][31] and a" fast" Pfr reaction (a few ps). [20,21,23,30,[32][33][34] The photoinduced Pr half-cycle is characterizedb yt he first electronic ground-state intermediate lumi-R (already in ZZE configuration) with red-shifted absorption spectrum and consecutive, thermally driven reaction steps on the ms-to-ms time scale involving meta-Ra, meta-Rc and finally Pfr.…”

Steric Effects Govern the Photoactivation of Phytochromes

“…[5][6][7][8] To day, although directe vidence is scarce, it is widely accepted that the photoisomerization occurs at the C15ÀC16b ond of the methine bridge between pyrrole rings C and D, thus corresponding to ar otation of ring Da roundt his bond. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] Such am echanism is supported by X-ray crystallographic data [9-13, 15, 16, 19, 21] ands tudies using av ariety of spectroscopic techniques such as circulard ichroism, [14] resonance Raman (RR), [17] femtosecondv isible-pumpi nfrared probe, [18] magic angle spinning NMR, [20] and femtosecond-to-microsec-ond transient absorption [22] spectroscopy.F or example, crystal structures of Pr forms of bacterial, [9-11, 16, 21] cyanobacterial, [12,15] and plant [19] phytochromess how that while rings AÀCa re tightlyp acked by the surrounding protein, ring Dr esides in ac avity that seems to more easily accommodate ar otation aroundt he C15ÀC16b ond. Furthermore,i nc ontrastt os olution-phase NMR data on Synechococcus OS-B' (a cyanobacterium) phytochrome that, af ew years ago, were taken as support for an alternative mechanismi nw hich the photoisomerization rather involves ar otation of ring A, [23] recently reported magic angle spinning NMR data on the same phytochrome are indeed consistent with the view that the photoisomerization takes place at the C15ÀC16 bond.…”