Biology subjects

Schlau-Cohen, G. S.

Publications and source records attributed to Schlau-Cohen, G. S..

3 recordsLinked to original sources

bioRxiv2023

Energetic driving force for LHCII clustering in plant membranes

Plants protect themselves against photodamage from excess energy using a process known as non-photochemical quenching (NPQ). A significant fraction of NPQ is induced by a {Delta}pH across the membrane, which changes the conformation, composition, and organization of the antenna complexes. In particular, clustering of the major light-harvesting complex (LHCII) has been observed, yet the thermodynamic driving force behind this reorganization has not been determined, largely because measurements of membrane protein interaction energies have not been possible. Here, we introduce a method to quantify membrane protein interaction energies and its application to the thermodynamics of LHCII clusters. By combining single-molecule measurements of LHCII-proteoliposomes at different protein densities and a rigorous analysis of LHCII clusters and photophysics, we quantified the LHCII-LHCII interaction energy to be approximately -5 kBT at neutral pH and at least -7 kBT at acidic pH. From these values, we found the thermodynamic driving force for LHCII clustering was dominated by these enthalpic contributions. Collectively, this work captures the membrane protein-protein interactions responsible for LHCII clustering from the perspective of equilibrium statistical thermodynamics, which has a long and rich tradition in biology.

biophysics↗

bioRxiv2023

Single-molecule acceptor rise time (smART) FRET for nanoscale distance sensitivity

The structure, dynamics, and binding of individual biomolecules have been extensively investigated using single-molecule Forster resonance energy transfer (smFRET) as a spectroscopic ruler. The FRET efficiency between a fluorophore pair is used to measure distances in the several nanometer range. Existing approaches to detect closer distances come at the expense of sensitivity to longer distances. Here, we introduce single-molecule acceptor rise-time (smART) FRET that spans closer and longer distances. The acceptor rise time encodes the FRET rate, which scales polynomially with distance and thus has a steep dependence that expands the working range by 50%. High precision and accuracy is achieved through the spectroscopic separation between the rise time and the photophysical fluctuations that obfuscate other FRET readouts. Using the nanoscale sensitivity, we resolved the architectures of DNA bound to the single-stranded binding protein from E. coli, demonstrating the ability of smART FRET to elucidate the complex behaviors of biomolecules.

biophysics↗

bioRxiv2021

Ligand-induced transmembrane conformational coupling in monomeric EGFR

Single pass cell surface receptors regulate cellular processes by transmitting ligand-encoded signals across the plasma membrane via changes to their extracellular and intracellular conformations. While receptor-receptor interactions are established as key aspects of transmembrane signaling, the contribution from the single helix of a monomeric receptor has been challenging to isolate due to the complexity and ligand-dependence of the receptor-receptor interactions. By combining membrane nanodiscs produced wtih cell-free expression, single-molecule Forster Resonance Energy Transfer measurements, and molecular dynamics simulations, we report that ligand binding induces intracellular conformational changes within monomeric, full-length epidermal growth factor receptor (EGFR). Our observations establish the existence of extracellular/intracellular conformational coupling within a single receptor molecule. We implicate a series of electrostatic interactions in the conformational coupling and find the coupling is inhibited by targeted therapeutics and mutations that also inhibit phosphorylation in cells. Collectively, these results introduce a facile mechanism to link the extracellular and intracellular regions through the single transmembrane helix of monomeric EGFR, and raise the possibility that intramolecular transmembrane conformational changes are common to single-pass membrane proteins.

biophysics↗