Distinct features of PsbS essential for mediating plant photoprotection.

Abstract

For optimum photosynthetic productivity it is crucial for plants to swiftly transition between light harvesting and photoprotective states as light conditions change in the field. The PsbS protein plays a pivotal role in this process by switching the light harvesting antenna, LHCII, into the photoprotective state, qE, to avoid photoinhibition in high light environment. However, the molecular mechanism of PsbS action upon LHCII have remained unclear. In our study, we identified its specific aminoacid domains that are essential for the function. Using the aminoacid point-mutagenesis of PsbS in vivo we found that the activation of photoprotection involves dynamic changes in the oligomeric state and conformation of PsbS, with two residues, E67 and E173, playing a key role in this process. Further, the replacement of hydrophobic phenylalanine residues in transmembrane helixes II (F83, F84, F87) and IV (F191, F193, F194) with tyrosine revealed that phenylalanine localised in helix IV could play a significant role in hydrophobic interactions of PsbS with LHCII. The removal of the 3₁₀ helix (H3) aminoacids I74, Y75, E76 did not affect the amplitude but resulted in a strongly delayed recovery of qE in darkness. These findings provide new insights into the molecular architecture of PsbS that are essential for regulating light harvesting in higher plants. Moreover, the combination of experimental mutagenesis with AI-assisted protein folding evolutionary scale model approach (ESMFold) opens new avenues for intelligently manipulating protein functions in silico to streamline and evaluate the experimental point mutagenesis strategies.