Wackenhut, F. | Search bioRxiv

bioRxiv2019

Quantum coherence in the photosynthesis apparatus of living cyanobacteria

The first step in photosynthesis is an extremely efficient energy transfer mechanism, which is difficult to be explained by classical short-range energy migration ("hopping") and led to the debate to which extent quantum coherence is involved in the energy transfer between the photosynthetic pigments. Embedding living cyanobacteria between the mirrors of an optical microresonator and using low intensity white light irradiation we observe vacuum Rabi splitting in the transmission and fluorescence spectra as a result of strong light matter coupling of the chlorophyll and the resonator modes. The Rabi-splitting scales with the number of chlorophyll a pigments involved in coherent coupling indicating forming a polaritonic state which is delocalized over the entire cyanobacterial thylakoid system, down to the single photon level. Our data provide evidence that a delocalized polaritonic state is the basis of the extremely high energy transfer efficiency under natural conditions.

biophysics↗

bioRxiv2019

Three-fluorophore FRET-FLIM enables the study of trimeric protein interactions and complex formation with nanoscale resolution in living plant cells

Protein-protein interaction studies provide valuable insights into cellular signaling. The well-studied brassinosteroid (BR) signaling is initiated by the hormone-binding receptor Brassinosteroid Insensitive 1 (BRI1) and its co-receptor BRI1 Associated Kinase 1 (BAK1). BRI1 and BAK1 were shown to interact independently with the Receptor-Like Protein 44 (RLP44), which is implicated in BRI1/BAK1-dependent cell wall integrity perception. To demonstrate the proposed complex formation of BRI1, BAK1 and RLP44, we established three-fluorophore intensity-based spectral Forster resonance energy transfer (FRET) and FRET-fluorescence lifetime imaging microscopy (FLIM) for living plant cells. Our evidence indicates that RLP44, BRI1 and BAK1 form a ternary complex in a distinct plasma membrane nanodomain. In contrast, although the immune receptor Flagellin Sensing 2 (FLS2) also forms a heteromer with BAK1, the FLS2/BAK1 complexes are localized in other nanodomains. In general, our three-fluorophore FRET approaches provide a feasible basis for studying the interaction and sub-compartmentalization of proteins in great detail.

plant biology↗