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To resolve how structural subunit diversity governs energy flow in photosynthetic systems, this study investigates the functional divergence between the minor antenna complex CP29 and the major antenna subunit Lhcb1 in Photosystem II. By pairing two-dimensional electronic-vibrational spectroscopy with lifetime density analysis and structure-based kinetic modeling, the authors directly mapped excitonic states to molecular structures and tracked excitation pathways. The results reveal that minor variations in pigment composition drastically reshape network topology, endowing CP29 with more spatially connected and reversible energy transfer routes that dynamically distribute excitation between the core and periphery.
Near-identical protein frameworks can switch from localized energy funnels into highly reversible, bidirectional routing networks through subtle, localized pigment substitutions.
Photosystem II (PSII) contains a diverse array of pigment-protein subunits with specialized roles in the antenna network. We investigate the functional significance of this subunit diversity in two structurally similar yet functionally distinct PSII subunits: minor light-harvesting complex CP29 and major light-harvesting complex LHCII. We combine two-dimensional electronic-vibrational spectroscopy with lifetime density analysis and structure-based kinetic modeling to assign spectral features to exciton states, providing molecular detail to probed spectral features. We show how the distinct pigment compositions of CP29 and Lhcb1, a monomeric subunit of the major LHCII trimer, reshape excitonic connectivity and energy transfer pathways in the complexes. Compared to Lhcb1, energy transfer pathways in CP29 are more spatially connected and reversible, suggesting CP29 evolved to distribute excitation between the core and periphery of the PSII antenna. We find that small structural modifications from a common framework tune CP29 and Lhcb1 to complementary roles in the PSII supercomplex.