The molecular pH-response mechanism of the plant light-stress sensor PsbS

Maithili Krishnan-Schmieden,Anjali Pandit,John T M Kennis,Patrick E Konold

doi:10.1038/s41467-021-22530-4

Maithili Krishnan-Schmieden, Anjali Pandit + Show 2 more

Open Access

https://doi.org/10.1038/s41467-021-22530-4

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Abstract

Plants need to protect themselves from excess light, which causes photo-oxidative damage and lowers the efficiency of photosynthesis. Photosystem II subunit S (PsbS) is a pH sensor protein that plays a crucial role in plant photoprotection by detecting thylakoid lumen acidification in excess light conditions via two lumen-faced glutamates. However, how PsbS is activated under low-pH conditions is unknown. To reveal the molecular response of PsbS to low pH, here we perform an NMR, FTIR and 2DIR spectroscopic analysis of Physcomitrella patens PsbS and of the E176Q mutant in which an active glutamate has been replaced. The PsbS response mechanism at low pH involves the concerted action of repositioning of a short amphipathic helix containing E176 facing the lumen and folding of the luminal loop fragment adjacent to E71 to a 310-helix, providing clear evidence of a conformational pH switch. We propose that this concerted mechanism is a shared motif of proteins of the light-harvesting family that may control thylakoid inter-protein interactions driving photoregulatory responses.

Highlights

Plants need to protect themselves from excess light, which causes photo-oxidative damage and lowers the efficiency of photosynthesis
Three P. patens Photosystem II subunit S (PsbS) mutants were constructed, in which the active Glu were mutated to Gln: E71 was replaced by Q (E71Q), E176Q and the double mutant E71Q/ E176Q, further denoted as mutation of Glu-1 only (M1) (E71Q), M2 (E176Q), and M1/M2 (E71Q/E176Q)
We selected pH 5.0 as the low pH condition to allow a direct comparison with the X-ray structure, which was resolved at pH 5.0, even though this is below the physiologically relevant pH range within which PsbS seems to work in vivo[22]

Summary

Introduction

Plants need to protect themselves from excess light, which causes photo-oxidative damage and lowers the efficiency of photosynthesis. The wild-type FTIR spectrum at pD 7.5 (Fig. 3a, orange line) shows that the Amide I band is centered at 1640 cm−1 with a broad shoulder at frequencies up to 1690 cm−1, indicative of predominant helical and loop contributions[26], consistent with the X-ray structure[20] and CD data[21].

Results

Conclusion