Fluorescence Decay Kinetics of Wild Type and D2-H117N Mutant Photosystem II Reaction Centers Isolated from Chlamydomonas reinhardtii

Abstract

We compare the chlorophyll fluorescence decay kinetics of the wild type and the D2-H117N mutant photosystem II reaction centers isolated from Chlamydomonas reinhardtii. The histidine residue located at site 117 on the D2 polypeptide of photosystem II is a proposed binding site for one of two peripheral accessory chlorophylls located in the reaction center complex. The peripheral accessory chlorophylls are thought to be coupled with the primary electron donor, P680, and thus involved in energy transfer with P680. The conservative replacement of the histidine residue with an asparagine residue allows the chlorophyll to remain bound to the reaction center. However, slight changes in the structural organization of the reaction center may exist that can affect the energy transfer kinetics. We show that the D2-H117N mutation causes a shift in the 20−30 ps lifetime component that has been associated with energy equilibration among coupled chlorophylls in the photosystem II reaction center.

Photosystem II Peripheral Accessory Chlorophyll Mutants inChlamydomonas reinhardtii. Biochemical Characterization and Sensitivity to Photo-Inhibition,

“…We previously demonstrated that the Chl coordinated by the D2-H117 residue was involved in energy transfer to the primary donor, P680 (Johnston et al, 2000). Relative to wild type, we observed a shift in the 30-ps Chl fluorescence decay lifetime component to 10 ps in D2-H117 mutants consistent with an alteration in energy transfer from the Chl coordinated by this residue to P680 (Schelvis et al, 1994;Johnston et al, 2000).…”

“…2 Lifetimes ( was dominated by contributions from the slower lifetime components relative to wild type. Unlike the D2-H117N mutant, however, there was no major shift in any single Chl fluorescence lifetime component in the Chl fluorescence decay kinetics of D1-H118Q reaction center particles (Johnston et al, 2000). It is significant that the amplitudes of the slower Chl fluorescence decay lifetime components were greater for the D1-H118Q mutant than in wild type.…”

“…It had been demonstrated previously that the 30-ps Chl fluorescence lifetime component attributed to energy transfer from the peripheral accessory Chl to P680 was altered in D2-H117N PSII reaction centers (Johnston et al, 2000). The mutation-induced alteration in energy transfer kinetics was attributed to a change in the distance or orientation of the peripheral accessory Chl relative to P680.…”

“…These histidines are not conserved in the analogous L and M polypeptides of the bacterial reaction center (for review, see Ruffle and Sayre, 1998). Site-directed mutagenesis studies in Chlamydomonas reinhardtii and Synechocystis PCC6803, and the recently resolved 3.8-Å crystal structure of the Synechococcus elongatus PSII core complex, subsequently demonstrated that the D1-H118 and D2-H117 residues coordinate the additional Chls associated with the PSII D1 and D2 proteins (Hutchison and Sayre, 1995;Cua et al, 1998;Lince and Vermaas, 1998;Schweitzer et al, 1998;Ruffle et al, 1999;Johnston et al, 2000;Zouni et al, 2001). Unlike the Chls involved in primary charge separation, the Chls coordinated by the D1-H118 and D2-H117 residues are located on the exterior of the D1-D2 heterodimer approximately midway across the thylakoid membrane and hence are designated the peripheral accessory Chls ( Fig.…”

“…Two functions have been proposed for the PSII peripheral accessory Chls: (a) mediation of energy transfer from the proximal antennae complexes (CP43 and CP47) to P680, and (b) participation in a low quantum-yield electron transfer cycle around PSII that protects the complex from photo-inhibition (Koulougliotis et al, 1994;Hutchison and Sayre, 1995;Schweitzer and Brudvig, 1997;Cua et al, 1998;Lince and Vermaas, 1998;Ruffle et al, 1999;Johnston et al, 2000). We previously demonstrated that the Chl coordinated by the D2-H117 residue was involved in energy transfer to the primary donor, P680 (Johnston et al, 2000).…”