Biology subjects

Mehra, H. S.

Publications and source records attributed to Mehra, H. S..

3 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

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↗

bioRxiv2024

Engineering the cyanobacterial ATP-driven BCT1 bicarbonate transporter for functional targeting to C3 plant chloroplasts

The ATP-driven bicarbonate transporter 1 (BCT1), a four-component complex in the cyanobacterial CO2-concentrating mechanism, could enhance photosynthetic CO2 assimilation in plant chloroplasts. However, directing its subunits (CmpA, CmpB, CmpC and CmpD) to three chloroplast sub-compartments is highly complex. Investigating BCT1 integration into Nicotiana benthamiana chloroplasts revealed promising targeting strategies using transit peptides from the intermembrane space protein Tic22 for correct CmpA targeting, while the transit peptide of the chloroplastic ABCD2 transporter effectively targeted CmpB to the inner envelope membrane. CmpC and CmpD were targeted to the stroma by RecA and recruited to the inner envelope membrane by CmpB. Despite successful targeting, expression of this complex in CO2-dependent Escherichia coli failed to demonstrate bicarbonate uptake. We then used rational design and directed evolution to generate new BCT1 forms that were constitutively active. Several mutants were recovered, including a CmpCD fusion. Selected mutants were further characterized and stably expressed in Arabidopsis thaliana, but the transformed plants did not have higher carbon assimilation rates or decreased CO2 compensation points in mature leaves. While further analysis is required, this directed evolution and heterologous testing approach presents potential for iterative modification and assessment of CO2-concentrating mechanism components to improve plant photosynthesis. HighlightWe describe the directed evolution and rational design of a cyanobacterial four-component bicarbonate transporter and the localization of its subunits to various chloroplast sub-compartments for improving C3 plant photosynthesis.

plant biology↗