Biology subjects

Brininger, C. M.

Publications and source records attributed to Brininger, C. M..

4 recordsLinked to original sources

bioRxiv2026

Multiple routes to red-shifted chlorophyll d-based photosynthesis

Strains of the cyanobacterium Acaryochloris marina exhibit diverse far-red light-harvesting properties during chlorophyll d-based photosynthesis. Here, we show that differences in light absorption among A. marina strains arise exclusively from Photosystem I (PSI) and reflect variation in multiple low-energy chlorophyll states. Time-resolved fluorescence reveals different combinations of low-energy states among strains, generating a continuum of spectral phenotypes. Cryo-EM structures of PSI at [~]1.8 [A] resolution reveal similar low-energy states arising from distinct pigment environments, demonstrating that red-shifted absorption is not governed by a single conserved motif. Phylogenetic analyses show that spectral tuning evolved through modular variation and reassortment of PSI components. These results indicate that distinct pigment configurations can converge on similar low-energy states, extending light harvesting near the energetic limit of oxygenic photosynthesis.

biophysics↗

bioRxiv2026

Cryo-EM structures of photosystem I with alternative quinones reveals new insight into cofactor selectivity

Quinones are an integral component of electron transfer processes in photosynthetic and mitochondrial respiratory proteins. One such photosynthetic protein, Photosystem I, is an essential photooxidoreductase found in all oxygenic phototrophs. To better understand quinone chemistry and to form a basis for protein engineering, the menB gene in the model cyanobacterium Synechocystis sp. PCC 6803 was interrupted, blocking the biosynthesis of phylloquinone and causing it to be replaced by exchangeable plastoquinone-9 in the A1A and A1B quinone-binding sites of Photosystem I. This genetic variant has been instrumental in bioenergy research, enabling incorporation of a range of substituted and isotopically labeled quinones. Despite numerous valuable studies, the interpretation of biophysical data has been limited by a lack of structural data. To address this, we present the high-resolution cryo-EM structures of Photosystem I from the {Delta}menB variant containing (a) exchangeable plastoquinone-9 and (b) exogenously added 2-ethyl-1,4-napthoquinone at 1.90- and 2.05-[A] resolution, respectively. Unexpectedly, the quinones in the A1A and A1B sites of Photosystem I, previously believed to have similar binding affinities, are found to be asymmetric in their ability to bind and exchange plastoquinone-9. This work reveals new and important insight into the molecular basis for Photosystem I activity in the {Delta}menB variant, the power of metabolic plasticity to maintain protein stability, and the requirement for protein instability to facilitate ligand exchange.

biochemistry↗

bioRxiv2026

Molecular design principles for Photosystem I-based biohybrid solar fuel catalysts

Direct solar-to-chemical conversion offers a compelling route to clean, dispatchable energy. Photosystem I (PSI), an evolutionarily optimized light-driven oxidoreductase central to oxygenic photosynthesis, can be repurposed for direct solar-fuel production by efficiently coupling its photochemistry to catalysts, thereby storing sunlight as chemical energy in the H-H bond of H2. One promising architecture integrates PSI with Pt nanoparticle (PtNP) catalysts to create photocatalytic PSI-PtNP biohybrids. Advancing these systems requires molecular-level insight into protein-nanoparticle interactions and the bio-nano electron transfer pathways that govern activity; however, progress has been constrained by limited structural data to guide rational design. Here, we present two molecular structures of active PSI-PtNP assemblies that (a) compare thermophilic and mesophilic PSI scaffolds and (b) probe how removal of the terminal [4Fe-4S] clusters and stromal subunits in PSI reshapes protein-nanoparticle interfaces and photocatalysis. Structural analyses and molecular dynamics simulations define the interface topology, electrostatics, and cofactor-to-nanoparticle distances, revealing key molecular features that control biohybrid formation and electron transfer efficiency. These data establish mechanistic links between scaffold composition, bio-nano interface geometry, and catalytic performance, yielding design principles for optimizing PSI-PtNP architectures. The resulting structure-function insights provide a blueprint for engineering PSI-based solar-fuels systems and, more broadly, inform the design of protein-nanomaterial interfaces for light-driven catalysis.

biophysics↗

bioRxiv2025

Calcite Precipitation by a Nitrogen-Fixing Cyanobacterium

Microbiologically induced calcium carbonate precipitation (MICP) is the process through which the metabolic activity of microorganisms causes the precipitation of calcium carbonate, which can result in solidification of sediment. In cyanobacteria, MICP is thought to occur primarily because cells sequester bicarbonate for the photosynthetic process, thereby lowering the pH of the surrounding media. However, these mechanisms are still poorly understood. Here we show direct evidence of MICP caused by the filamentous cyanobacterium Anabaena. Anabaena differentiates into photosynthetic vegetative cells and nitrogen-fixing heterocysts. Using quantitative microscopy, we show that MICP occurs due to two distinct mechanisms: Firstly, mechanical stress on vegetative cells can cause leakage and/or lysis, releasing sequestered bicarbonate into the environment, resulting in formation of new crystals. Secondly, contact between a heterocyst and a calcite crystal seed appears to cause rapid crystal growth. Our results suggest an evolutionary benefit of contact-mediated precipitation to anchor cyanobacteria growing in tidal regions. By providing greater insight into MICP caused by Anabaena, these results could be used to optimize bio-cement production, thereby enabling a green construction material that could assist with carbon sequestration and reducing the impact of climate change.

microbiology↗