Core Antenna CP47 Research Articles

Protein Dynamics in Photosystem II Complexes of Green Plants Studied by Time-Resolved Hole-Burning

We have studied the protein dynamics of three subcore reaction-center complexes of photosystem II: the isolated reaction center (RC), the core antenna CP47, and the CP47 RC complex by means of time-resolved hole-burning in the red wing of their Qy-absorption bands. The dependence of the “effective” homogeneous line width on temperature T between 1.2 and 4.2 K suggests that optical dephasing in these proteins is determined by two-level systems (TLSs), as in doped organic glasses. By contrast, the increase of as a function of delay time td (between burning and probing the hole) from 10-5 to 105 s, caused by spectral diffusion (SD), differs from that in glasses and is characteristic for each complex. CP47 RC does not undergo any SD over 10 decades in time for T ≤ 4.2 K, i.e., = constant at a given temperature. Although CP47 and the RC do not show SD for td ≤ 1 s, they do for longer delay times, with increasing logarithmically with td. The onset and amount of SD appear to be correlated with the mass of the protein. We conclude that only slow motions, related to TLSs located at the more flexible surface of the protein (with a broad and continuous distribution of rates R < 1−3 Hz), contribute to SD at long delay times and that the whole protein, or a substantial part of it, is involved in SD. Fast, local fluctuations associated with a rigid, crystalline-like inner protein core are responsible for “pure” dephasing at short td.

Spectral Distributions of “Trap” Pigments in the RC, CP47, and CP47−RC Complexes of Photosystem II at Low Temperature: A Fluorescence Line-Narrowing and Hole-Burning Study

Broad-band absorption and fluorescence, fluorescence line-narrowing (FLN), and spectral hole-burning experiments have been performed on the Qy-band of three subcore reaction-center complexes of photosystem II between 1.2 and 4.2 K: the isolated reaction center (RC), the inner core antenna CP47, and the CP47−RC complex. In the RC, fluorescence line-narrowing (FLN) is observed for excitation wavelengths λexc ≥ 676 nm, whereas in CP47, this occurs for λexc ≥ 680 nm. The FLN spectra of CP47−RC appear to be the sum of the individual spectra of the RC and CP47, an indication that this complex has two “traps”. This has been confirmed from the spectral distributions obtained by measuring the hole depth (at constant hole width) as a function of λexc, as previously done for the RC [Groot, M. L., et al. J. Phys. Chem. 100, 1996, 11488]. The maxima of these distributions are at ∼682 nm for the RC “trap” and at ∼690 nm for the CP47 “trap” within the CP47−RC complex. Further support that the two distributions of pigme...