Biology subjects

Richardson, K. H.

Publications and source records attributed to Richardson, K. H..

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↗

bioRxiv2021

Functional basis of electron transport within photosynthetic complex I

Photosynthesis and respiration rely upon a proton gradient to produce ATP. In photosynthesis, the Respiratory Complex I homologue, Photosynthetic Complex I (PS-CI) is proposed to couple ferredoxin oxidation and plastoquinone reduction to proton pumping across thylakoid membranes, and is fundamental to bioenergetics in photosynthetic bacteria and some higher plant cell types. However, little is known about the PS-CI molecular mechanism and attempts to understand its function have previously been frustrated by its large size and high lability. Here, we overcome these challenges by pushing the limits in sample size and spectroscopic sensitivity, to determine arguably the most important property of any electron transport enzyme - the reduction potentials of its cofactors, in this case the iron-sulphur clusters of PS-CI, and unambiguously assign them to the structure using double electron-electron resonance (DEER). We have thus determined the bioenergetics of the electron transfer relay and provide insight into the mechanism of PS-CI, laying the foundations for understanding of how this important bioenergetic complex functions.

biophysics↗

bioRxiv2019

Microbial degradation of plastic in aqueous solutions demonstrated by CO2 evolution and quantification.

The environmental accumulation of plastics worldwide is a consequence of the durability of the material. Alternative polymers, marketed as biodegradable, present a potential solution to mitigate their ecological damage. However, understanding of biodegradability has been hindered by a lack of reproducible testing methods. Here, we present a new approach to assess biodegradability by monitoring bacterial respiration, in an aqueous media supplemented with a polymer as a single carbon source. Rhodococcus rhodochrous and Alcanivorax borkumensis are good model organisms for soil and marine systems respectively, allowing simulations of plastic biodegradation in these key environments. We demonstrate that polymer molecular weight reduction is the critical factor in the biodegradability of low-density polyethylene. Additionally, we tested a wide variety of plastics, including environmentally weathered and laboratory aged samples, using the same method allowing direct comparisons of the relative biodegradability of various polymers.

ecology↗