Structure-Based Exciton Hamiltonian and Dynamics for the Reconstituted Wild-type CP29 Protein Antenna Complex of the Photosystem II

Abstract

We provide an analysis of the pigment composition of reconstituted wild type CP29 complexes. The obtained stoichiometry of 9 ± 0.6 Chls a and 3 ± 0.6 Chls b per complex, with some possible heterogeneity in the carotenoid binding, is in agreement with 9 Chls a and 3.5 Chls b revealed by the modeling of low-temperature optical spectra. We find that ∼50% of Chl b614 is lost during the reconstitution/purification procedure, whereas Chls a are almost fully retained. The excitonic structure and the nature of the low-energy (low-E) state(s) are addressed via simulations (using Redfield theory) of 5 K absorption and fluorescence/nonresonant hole-burned (NRHB) spectra obtained at different excitation/burning conditions. We show that, depending on laser excitation frequency, reconstituted complexes display two (independent) low-E states (i.e., the A and B traps) with different NRHB and emission spectra. The red-shifted state A near 682.4 nm is assigned to a minor (∼10%) subpopulation (sub. II) that most likely originates from an imperfect local folding occurring during protein reconstitution. Its lowest energy state A (localized on Chl a604) is easily burned with λ = 488.0 nm and has a red-shifted fluorescence origin band near 683.7 nm that is not observed in native (isolated) complexes. Prolonged burning by 488.0 nm light reveals a second low-E trap at 680.2 nm (state B) with a fluorescence origin band at ∼681 nm, which is also observed when using a direct low-fluence excitation near 650 nm. The latter state is mostly delocalized over the a611, a612, a615 Chl trimer and corresponds to the lowest energy state of the major (∼90%) subpopulation (sub. I) that exhibits a lower hole-burning quantum yield. Thus, we suggest that major sub. I correspond to the native folding of CP29, whereas the red shift of the Chl a604 site energy observed in the minor sub. II occurs only in reconstituted complexes.

Time-dependent atomistic simulations of the CP29 light-harvesting complex

“…Since CAM-B3LYP is a long-range corrected DFT functional, the site energies obtained employing this approach are quite similar to our TD-LC-DFTB calculations. In the case of the calculations by Müh et al, 30 the results are accurately matching the findings by Jassas et al 82 This agreement is due to the fact that the TrESP approach was applied in 31 Müh et al, 30 Jassas et al, 82 and Mascoli et al 83 both studies to calculate the excitonic couplings and energies. Subsequently, the absorption spectrum was fitted to determine the site energies.…”

“…As mentioned above, the results based on DFT approaches clearly show an overall overestimation of the excitation energy gaps, which is also reflected in a shift in site energies compared to the experimental outcomes. For this reason, we introduced a common shift for our site energies toward the experimental values and compared with measurements by Jassas et al 82 and Mascoli et al 83 The shifted energies are depicted in Fig. S4.…”

“…The residues 602, 603, 604, 609, 610, 611, 612, 613, and 615 refer to Chl-a molecules (green), while the residues 606, 607, 608, and 614 refer to Chl-b molecules (red). (b) Comparison with other computed site energies for the CP29 complex by Jurinovich et al,31 Müh et al,30 Jassas et al,82 and Mascoli et al83…”

Time-Dependent Atomistic Simulations of the CP29 Light-Harvesting Complex

“…Since CAM-B3LYP is a long-range corrected DFT functional, the site energies obtained employing this approach, are quite similar to our TD-LC-DFTB calculations. In case of the calculations by Müh et al 30 , the results are accurately matching the findings by Jassas et al 82 . This agreement is due to the fact that the TrESP approach was applied in both studies to calculate the excitonic couplings and energies.…”

Structural and functional differentiation of the light‐harvesting protein Lhcb4 during land plant diversification

“…B). The Chl b 614, despite apparently quite excitonically isolated from the other Chls in the protein (Jassas et al ), represents the crossway in the energy transfer pathways within the C 2 S 2 M 2 supercomplex, being the closest pigment to either the Chl b 606 of Lhcb6 or the Chl a 614 of Lhcb3 (Su et al ). This histidine residue is well conserved in Lhcb4 sequences of angiosperms and bryophytes that clustered with the Lhcb4.1/4.2 isoforms of Arabidopsis (Fig.…”