Structural diversity and modularity of photosynthetic RC−LH1 complexes

Bacterial photosynthesis is essential for sustaining life on Earth as it aids in carbon assimilation, atmospheric composition, and ecosystem maintenance. Many bacteria utilize anoxygenic photosynthesis to convert sunlight into chemical energy while producing organic matter. The core machinery of anoxygenic photosynthesis performed by purple photosynthetic bacteria and Chloroflexales is the reaction center−light-harvesting 1 (RC−LH1) pigment–protein supercomplex. In this review, we discuss recent structural studies of RC−LH1 core complexes based on the advancement in structural biology techniques. These studies have provided fundamental insights into the assembly mechanisms, structural variations, and modularity of RC−LH1 complexes across different bacterial species, highlighting their functional adaptability. Understanding the natural architectures of RC−LH1 complexes will facilitate the design and engineering of artificial photosynthetic systems, which can enhance photosynthetic efficiency and potentially find applications in sustainable energy production and carbon capture

Cryo-EM structure of a monomeric RC-LH1-PufX supercomplex with high-carotenoid content from Rhodobacter capsulatus

xclusively monomers in which the RC is surrounded by a 15-subunit LH1 ring. Incorporation of a transmembrane polypeptide PufX leads to a large opening within the LH1 ring. Each LH1 subunit associates two carotenoids and two bacteriochlorophylls, which is similar to Rba. sphaeroides RC-LH1 but more than one carotenoid per LH1 in Rba. veldkampii RC-LH1 monomer. Collectively, the unique Rba. capsulatus RC-LH1-PufX represents an intermediate structure between Rba. sphaeroides and Rba. veldkampii RC-LH1-PufX. Comparison of PufX from the three Rhodobacter species indicates the important residues involved in dimerization of RC-LH1

Cryo-EM structure of the photosynthetic RC-LH1-PufX supercomplex at 2.8-angstrom resolution

The reaction center (RC)−light-harvesting complex 1 (LH1) supercomplex plays a pivotal role in bacterial photosynthesis. Many RC-LH1 complexes integrate an additional protein PufX that is key for bacterial growth and photosynthetic competence. Here, we present a cryo–electron microscopy structure of the RC-LH1-PufX supercomplex from Rhodobacter veldkampii at 2.8-Å resolution. The RC-LH1-PufX monomer contains an LH ring of 15 αβ-polypeptides with a 30-Å gap formed by PufX. PufX acts as a molecular “cross brace” to reinforce the RC-LH1 structure. The unusual PufX-mediated large opening in the LH1 ring and defined arrangement of proteins and cofactors provide the molecular basis for the assembly of a robust RC-LH1-PufX supercomplex and efficient quinone transport and electron transfer. These architectural features represent the natural strategies for anoxygenic photosynthesis and environmental adaptation

Fibrotic Marker Galectin-3 Identifies Males at Risk of Developing Cancer and Heart Failure

BACKGROUND: Cancer and heart failure (HF) are the leading causes of death in the Western world. Shared mechanisms such as fibrosis may underlie either disease entity, furthermore it is unknown whether this relationship is sex-specific.OBJECTIVES: We sought to investigate how fibrosis-related biomarker galectin-3 (gal-3) aids in identifying individuals at risk for new-onset cancer and HF, and how this differs between sexes.METHODS: Gal-3 was measured at baseline and at 4-year follow-up in 5,786 patients of the PREVEND (Prevention of Renal and Vascular Endstage Disease) study. The total follow-up period was 11.5 years. An increase of ≥50% in gal-3 levels between measurements was considered relevant. We performed sex-stratified log-rank tests and Cox regression analyses overall and by sex to evaluate the association of gal-3 over time with both new-onset cancer and new-onset HF.RESULTS: Of the 5,786 healthy participants (50% males), 399 (59% males) developed new-onset cancer, and 192 (65% males) developed new-onset HF. In males, an increase in gal-3 was significantly associated with new-onset cancer (both combined and certain cancer-specific subtypes), after adjusting for age, body mass index, hypertension, smoking status, estimated glomerular filtration rate, diabetes mellitus, triglycerides, coronary artery disease, and C-reactive protein (HR: 1.89; 95% CI: 1.32-2.71; P &lt; 0.001). Similar analyses demonstrated an association with new-onset HF in males (HR: 1.77; 95% CI: 1.07-2.95; P = 0.028). In females, changes in gal-3 over time were neither associated with new-onset cancer nor new-onset HF. CONCLUSIONS: Gal-3, a marker of fibrosis, is associated with new-onset cancer and new-onset HF in males, but not in females.</p

Structural basis for the assembly and quinone transport mechanisms of the dimeric photosynthetic RC-LH1 supercomplex

The reaction center (RC) and light-harvesting complex 1 (LH1) form a RC–LH1 core supercomplex that is vital for the primary reactions of photosynthesis in purple phototrophic bacteria. Some species possess the dimeric RC–LH1 complex with a transmembrane polypeptide PufX, representing the largest photosynthetic complex in anoxygenic phototrophs. However, the details of the architecture and assembly mechanism of the RC–LH1 dimer are unclear. Here we report seven cryo-electron microscopy (cryo-EM) structures of RC–LH1 supercomplexes from Rhodobacter sphaeroides. Our structures reveal that two PufX polypeptides are positioned in the center of the S-shaped RC–LH1 dimer, interlocking association between the components and mediating RC–LH1 dimerization. Moreover, we identify another transmembrane peptide, designated PufY, which is located between the RC and LH1 subunits near the LH1 opening. PufY binds a quinone molecule and prevents LH1 subunits from completely encircling the RC, creating a channel for quinone/quinol exchange. Genetic mutagenesis, cryo-EM structures, and computational simulations provide a mechanistic understanding of the assembly and electron transport pathways of the RC–LH1 dimer and elucidate the roles of individual components in ensuring the structural and functional integrity of the photosynthetic supercomplex

Structural basis for the assembly and electron transport mechanisms of the dimeric photosynthetic RC–LH1 supercomplex

AbstractThe reaction center (RC) and light-harvesting complex 1 (LH1) form a RC–LH1 core supercomplex that is vital for the primary reactions of photosynthesis in purple photosynthetic bacteria. Some species possess the dimeric RC–LH1 complex with an additional polypeptide PufX, representing the largest photosynthetic complex in anoxygenic phototrophs. However, the details of the architecture and assembly mechanism of the RC–LH1 dimer are unclear. Here we report seven cryo-electron microscopy (cryo-EM) structures of RC–LH1 supercomplexes from Rhodobacter sphaeroides. Our structures reveal that two PufX polypeptides are positioned in the center of the S-shaped RC–LH1 dimer, interlocking association between the components and mediating RC–LH1 dimerization. Moreover, we identify a new transmembrane peptide, designated PufY, which is located between the RC and LH1 subunits near the LH1 opening. PufY binds a quinone molecule and prevents LH1 subunits from completely encircling the RC, creating a channel for quinone/quinol exchange. Genetic mutagenesis, cryo-EM structures, and computational simulations enable a mechanistic understanding of the assembly and electron transport pathways of the RC–LH1 dimer and elucidate the roles of individual components in ensuring the structural and functional integrity of the photosynthetic supercomplex.</jats:p

Determining the Macromolecular Structures of Photosynthetic Supercomplexes from Rhodobacter using Cryo-Electron Microscopy

The reaction center (RC)−light-harvesting complex 1 (LH1) supercomplex plays a central role in bacterial photosynthesis by converting light into chemical energy. Some RC–LH1 complexes integrate an additional protein PufX which is key for bacterial growth and photosynthetic competence. This thesis presents the atomic models of RC−LH1−PufX complexes from three species of purple bacteria: Rhodobacter (Rba.) sphaeroides, Rba. veldkampii and Rba. capsulatus. Electron potential maps used to build the models were obtained by single particle cryo-electron microscopy at resolutions of 2.84 Å (Rba. veldkampii), 3.40 Å and 2.79 Å (Rba. sphaeroides), and 2.59 Å (Rba. capsulatus). The RC–LH1–PufX native monomers of Rba. veldkampii and Rba. capsulatus contain LH1 rings comprised of 15 αβ-heterodimers featuring a gap formed by PufX. The RC−LH1−PufX native dimer of Rba. sphaeroides contains an S-shaped LH1 ring of 28 αβ-heterodimers with two large gaps formed by PufX polypeptides, and an additional polypeptide PufY inserted between the LH1 ring and the RC near each gap. In order to understand the process of dimerization and the structural impacts of the additional polypeptides PufX and PufY, we also characterized the native monomer and three mutant complexes: one without the PufX, one without the PufY and one with PufX replaced with PufX of a strictly monomeric complex from Rba. veldkampii. The presented high-resolution WT and mutant structures provided insights into monomeric and dimeric RC‒LH1 complex formation, quinone pathway and roles of polypeptides PufX and PufY. PufX was observed to mediate dimerization through its N-terminus, correct complex assembly and halting the LH1 ring elongation resulting in a characteristic open architecture. PufY was observed to possibly stabilize the LH1 ring, increasing the efficiency of excitation energy transfer and potentially helping with quinone navigation. The features, similarities and differences displayed by RC‒LH1‒PufX complexes serve as a structural basis for understanding the mechanism of anoxygenic photosynthesis, as well as environmental adaptation and evolution of photosynthetic systems