Biology subjects

Nixon, P.

Publications and source records attributed to Nixon, P..

5 recordsLinked to original sources

bioRxiv2026

Spatiotemporal biogenesis of thylakoid membranes in the green alga Chlamydomonas reinhardtii

Thylakoid membranes are essential for oxygenic photosynthesis, yet the mechanisms underlying their spatial and temporal biogenesis remain poorly understood. Here, using a light-induced membrane regeneration system in Chlamydomonas reinhardtii, we generate a time-resolved map of thylakoid formation and photosynthetic complex assembly at unprecedented spatial and temporal resolution by integrating super-resolution fluorescence microscopy, cryo-electron tomography, proteomics, and spectroscopy. We show that thylakoid biogenesis is globally distributed and multipolar, with new membrane formation occurring at multiple sites across the chloroplast, including regions adjacent to the inner envelope membranes in both basal and lobe regions. We identify F-ATP synthase storage membranes and map the redistribution of translating ribosomes from T-zone enrichment to a chloroplast-wide distribution at early stages of thylakoid formation, consistent with decentralized synthesis of photosynthetic complexes. We further delineate the hierarchical assembly of photosystem supercomplexes, starting with formation of reaction centers. Together, these findings refine the spatial organization of photosynthetic membrane biogenesis and establish a unified spatiotemporal framework linking thylakoid formation, translational activation, and functional maturation, providing a mechanistic basis for plastid engineering to enhance photosynthetic efficiency.

Cell Biology↗

bioRxiv2024

Engineering Rubisco Condensation in Chloroplasts to Manipulate Plant Photosynthesis

Although Rubisco is the most abundant enzyme globally, it is inefficient for carbon fixation because of its low turnover rate and limited ability to distinguish CO2 and O2, especially under high O2 conditions. To address these limitations, phytoplankton, including cyanobacteria and algae, have evolved CO2-concentrating mechanisms (CCM) that involve compartmentalizing Rubisco within specific structures, such as carboxysomes in cyanobacteria or pyrenoids in algae. Engineering plant chloroplasts to establish similar structures for compartmentalizing Rubisco has attracted increasing interest for improving photosynthesis and carbon assimilation in crop plants. Here, we present a method to effectively induce the condensation of endogenous Rubisco within tobacco (Nicotiana tabacum) chloroplasts by genetically fusing superfolder green fluorescent protein (sfGFP) to the tobacco Rubisco large subunit (RbcL). By leveraging the intrinsic oligomerization feature of sfGFP, we successfully created pyrenoid-like Rubisco condensates that display dynamic, liquid-like properties within chloroplasts without affecting Rubisco assembly and catalytic function. The transgenic tobacco plants demonstrated comparable autotrophic growth rates and full life cycles in ambient air relative to the wild-type plants. Our study offers a promising strategy for modulating endogenous Rubisco assembly and spatial organization in plant chloroplasts via phase separation, which provides the foundation for generating synthetic organelle-like structures for carbon fixation, such as carboxysomes and pyrenoids, to optimize photosynthetic efficiency.

plant biology↗

bioRxiv2022

The Ycf48 accessory factor occupies the site of the oxygen-evolving manganese cluster during photosystem II biogenesis

Robust oxygenic photosynthesis requires a suite of accessory factors to ensure efficient assembly and repair of the oxygen-evolving photosystem two (PSII) complex. The highly conserved Ycf48 assembly factor binds to the newly synthesized D1 reaction center polypeptide and promotes the initial steps of PSII assembly, but its binding site is unclear. Here we have used cryo-electron microscopy to determine the structure of a cyanobacterial PSII D1/D2 reaction center assembly complex with Ycf48 attached. Ycf48, a 7-bladed beta propeller, binds to the amino-acid residues of D1 that ultimately ligate the Mn4CaO5 cluster that catalyzes water oxidation, thereby preventing the premature binding of Mn2+ and Ca2+ ions and protecting the site from damage. Interactions with D2 help explain how Ycf48 promotes assembly of the D1/D2 complex. Overall, our work provides new insights into the early stages of PSII assembly and the structural changes that create the binding site for the Mn4CaO5 cluster.

biochemistry↗

bioRxiv2021

Probing the biogenesis pathway and dynamics of thylakoid membranes

How thylakoid membranes are generated to form the metabolically active membrane network and how thylakoid membranes orchestrate the insertion and localization of protein complexes for efficient electron flux remain elusive. Here, we develop a method to modulate thylakoid biogenesis in the rod-shaped cyanobacterium Synechococcus elongatus PCC 7942 by modulating light intensity during cell growth, and probe the spatial-temporal stepwise biogenesis process of thylakoid membranes in cells. Our results reveal that the plasma membrane and regularly arranged concentric thylakoid layers have no physical connections. The newly synthesized thylakoid membrane fragments emerge between the plasma membrane and pre-existing thylakoids. Photosystem I monomers appear in the thylakoid membranes earlier than other mature photosystem assemblies, followed by generation of Photosystem I trimers and Photosystem II complexes. Redistribution of photosynthetic complexes during thylakoid biogenesis ensures establishment of the spatial organization of the functional thylakoid network. This study provides insights into the dynamic biogenesis process and maturation of the functional photosynthetic machinery.

plant biology↗

bioRxiv2020

Effective in-vitro inactivation of SARS-CoV-2 by commercially available mouthwashes

Infectious SARS-CoV-2 can be recovered from the oral cavities and saliva of COVID-19 patients with potential implications for disease transmission. Reducing viral load in patient saliva using antiviral mouthwashes may therefore have a role as a control measure in limiting virus spread, particularly in dental settings. Here, the efficacy of SARS-CoV-2 inactivation by seven commercially available mouthwashes with a range of active ingredients were evaluated in vitro. We demonstrate [≥]4.1 to [≥]5.5 log10 reduction in SARS-CoV-2 titre following a one minute treatment with commercially available mouthwashes containing 0.01-0.02% stabilised hypochlorous acid or 0.58% povidone iodine, and non-specialist mouthwashes with both alcohol-based and alcohol-free formulations designed for home use. In contrast, products containing 1.5% hydrogen peroxide or 0.2% chlorhexidine gluconate were ineffective against SARS-CoV-2 in these tests. This study contributes to the growing body of evidence surrounding virucidal efficacy of mouthwashes/oral rinses against SARS-CoV-2, and has important applications in reducing risk associated with aerosol generating procedures in dentistry and potentially for infection control more widely.

microbiology↗