Single-Molecule Identification of Quenched and Unquenched States of LHCII.
In photosynthetic light harvesting, absorbed sunlight is converted to electron flow with near-unity quantum efficiency under low light conditions. Under high light conditions, plants avoid damage to their molecular machinery by activating a set of photoprotective mechanisms to harmlessly dissipate excess energy as heat. To investigate these mechanisms, we study the primary antenna complex in green plants, light-harvesting complex II (LHCII), at the single-complex level. We use a single-molecule technique, the Anti-Brownian Electrokinetic trap, which enables simultaneous measurements of fluorescence intensity, lifetime, and spectra in solution. With this approach, including the first measurements of fluorescence lifetime on single LHCII complexes, we access the intrinsic conformational dynamics. In addition to an unquenched state, we identify two partially quenched states of LHCII. Our results suggest that there are at least two distinct quenching sites with different molecular compositions, meaning multiple dissipative pathways in LHCII. Furthermore, one of the quenched conformations significantly increases in relative population under environmental conditions mimicking high light.
†Department of Chemistry, Stanford University, Stanford, California 94305, United States.
Gabriela S
GS
Schlau-Cohen
†Department of Chemistry, Stanford University, Stanford, California 94305, United States.
Hsiang-Yu
HY
Yang
‡Department of Physics, University of Pretoria, Private bag X20, Hatfield 0028, South Africa.
Tjaart P J
TP
Krüger
§Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Pengqi
P
Xu
§Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Michal
M
Gwizdala
§Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Rienk
R
van Grondelle
§Department of Physics and Astronomy, Faculty of Sciences, VU University Amsterdam and LaserLab Amsterdam, De Boelelaan 1081, 1081 HV Amsterdam, The Netherlands.
Roberta
R
Croce
†Department of Chemistry, Stanford University, Stanford, California 94305, United States.
W E
WE
Moerner
D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology*
D045342:Light-Harvesting Protein Complexes
light harvesting; photoprotection; photosynthesis; single-molecule fluorescence spectroscopy