A Protein Environment-Modulated Energy Dissipation Channel in LHCII Antenna Complex

Abstract

Summary The major light-harvesting complex of photosystem II (LHCII) is the main contributor to sunlight energy harvesting in plants. The flexible design of LHCII underlies a photoprotective mechanism whereby this complex switches to a dissipative state in response to high light stress, allowing the rapid dissipation of excess excitation energy (non-photochemical quenching, NPQ). In this work, we locked single LHCII trimers in a quenched conformation after immobilization of the complexes in polyacrylamide gels to impede protein interactions. A comparison of their pigment excited-state dynamics with quenched LHCII aggregates in buffer revealed the presence of a new spectral band at 515 nm arising after chlorophyll excitation. This is suggested to be the signature of a carotenoid excited state, linked to the quenching of chlorophyll singlet excited states. Our data highlight the marked sensitivity of pigment excited-state dynamics in LHCII to structural changes induced by the environment.

Simultaneous Presence of Bacteriochlorophyll and Xanthorhodopsin Genes in a Freshwater Bacterium

“…The light-induced absorbance changes were driven by microsecond pulses monitored in the 400- to 700-nm range with microsecond temporal resolution over microsecond-to-second-long time delays. The transient absorption data were globally fit by a sum of exponential functions using Matlab (The MathWorks Inc. USA) scripts, and the confidence intervals of the resulting rate constants were estimated using bootstrap resampling as described previously ( 72 ).…”

Trivial Excitation Energy Transfer to Carotenoids is an Unlikely Mechanism for Non-Photochemical Quenching in LHCII

“…The picture gets even more complicated when one considers quenched LHCII in gel. It was recently shown that excitation of Q y results in the immediate appearance of a large-amplitude positive peak at 19, 417cm −1 (515nm) which we'll label A 515 [61]. This is not merely a shifted S 1 as direct excitation of Lut gave the usual S 1 ESA at 18, 500cm −1 (540nm), although A 515 is detectable at later times and may simply be initially hidden by S 1 .…”

“…However, as they point out, ε S 1 is not a free parameter and a protein-induced blue-shift of 14, 050 → 18, 000cm −1 (712 → 555nm) would be quite large. Saccon et al recently performed TA measurements on quenched LHCII immobilised in polyacrylamide gel (a model for NPQ) [61] and found that linear excitation of Lut (i.e. via S 2 ) produces the usual S 1 → S n ESA at ε S n − ε S 1 ≈ 18, 500cm −1 (540nm).…”

“…All transient absorption data were measured with a spectrometer described in detail in ref [61]. Lutein (Sigma Aldrich) was dissolved in spectroscopic grade pyridine to yield an optical density of 0.2 mm −1 at the absorption maximum.…”

An energy-dissipative state of the major antenna complex of plants

“…S2). It has previously been observed that LH1 and LH2 antenna rings in purple bacteria for example displayed a 50% shorter lifetime in vivo compared to in vitro (Ricci et al, 1996) and similarly that quenching in LHCII was dependent on its membrane environment (Moya et al, 2001, Natali et al, 2016, Saccon et al, 2020, Manna et al, 2021. Lifetimes of pigmentprotein complexes largely depend on their local environment, e.g.…”