DOI: 10.1101/457614Oct 31, 2018Paper

The two active glutamates of the plant stress sensor PsbS contribute non-equivalently to its pH-activated molecular response mechanism

BioRxiv : the Preprint Server for Biology
M KrishnanA Pandit

Abstract

The membrane protein Photosystem II subunit S (PsbS) is a pH sensor that plays an essential role in signaling light stress in plants to prevent photo oxidation and generation of detrimental reactive species. PsbS detects thylakoid lumen acidification in excess light conditions via two glutamates facing the lumen, however, its molecular mechanism for activation has remained elusive. We performed an infrared and 2-dimensional infrared spectroscopic analysis of wild type Physcomitrella patens PsbS and of mutants in which the active glutamates have been replaced: E71Q, E176Q (the equivalent of E69Q and E173Q in spinach PsbS) and the double mutant E71Q/E176Q. We discovered that E71 exerts allosteric control of PsbS dimerization, while E176 is essential for the secondary structural response to low pH. Based on our results, we propose a molecular pH response mechanism that involves re-positioning of the amphipathic short helix facing the lumen, whereby it moves from the aqueous phase into the hydrophobic membrane phase upon lowering the pH. This structural mechanism may be a shared motif of protein molecular switches of the light-harvesting family and its elucidation could open new routes for crops engineering to improve photosyntheti...Continue Reading

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