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

2021 ◽  
Author(s):  
Peng Cao ◽  
Laura Bracun ◽  
Atsushi Yamagata ◽  
Bern Christianson ◽  
Tatsuki Negami ◽  
...  
Keyword(s):  
Electron Transport ◽  
Structural Basis ◽  
Transport Mechanisms ◽  
Transport Pathways ◽  
Light Harvesting Complex ◽  
Anoxygenic Phototrophs ◽  
Purple Photosynthetic Bacteria ◽  
Cryo Electron Microscopy ◽  
Assembly Mechanism ◽  
Primary Reactions

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 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.

scholarly journals Structures of Rhodopseudomonas palustris RC-LH1 complexes with open or closed quinone channels

2021 ◽  
Vol 7 (3) ◽  
pp. eabe2631
Author(s):  
David J. K. Swainsbury ◽  
Pu Qian ◽  
Philip J. Jackson ◽  
Kaitlyn M. Faries ◽  
Dariusz M. Niedzwiedzki ◽  
...  
Keyword(s):  
Binding Sites ◽  
Rhodopseudomonas Palustris ◽  
Ring Closure ◽  
Light Harvesting Complex ◽  
The Core ◽  
Quinone Binding ◽  
Cryo Electron Microscopy ◽  
Unique Protein ◽  
Center Light ◽  
Resolution Structure

The reaction-center light-harvesting complex 1 (RC-LH1) is the core photosynthetic component in purple phototrophic bacteria. We present two cryo–electron microscopy structures of RC-LH1 complexes from Rhodopseudomonas palustris. A 2.65-Å resolution structure of the RC-LH114-W complex consists of an open 14-subunit LH1 ring surrounding the RC interrupted by protein-W, whereas the complex without protein-W at 2.80-Å resolution comprises an RC completely encircled by a closed, 16-subunit LH1 ring. Comparison of these structures provides insights into quinone dynamics within RC-LH1 complexes, including a previously unidentified conformational change upon quinone binding at the RC QB site, and the locations of accessory quinone binding sites that aid their delivery to the RC. The structurally unique protein-W prevents LH1 ring closure, creating a channel for accelerated quinone/quinol exchange.

scholarly journals Structural basis for the regulation of nucleosome recognition and HDAC activity by histone deacetylase assemblies

2021 ◽  
Vol 7 (2) ◽  
pp. eabd4413
Author(s):  
Jung-Hoon Lee ◽  
Daniel Bollschweiler ◽  
Tillman Schäfer ◽  
Robert Huber
Keyword(s):  
Transcriptional Repression ◽  
Histone Deacetylases ◽  
Active Sites ◽  
Chromatin Modification ◽  
Structural Basis ◽  
Amino Terminal ◽  
Cryo Electron Microscopy ◽  
Multiple Contacts ◽  
Lysine Residues ◽  
Nucleosome Binding

The chromatin-modifying histone deacetylases (HDACs) remove acetyl groups from acetyl-lysine residues in histone amino-terminal tails, thereby mediating transcriptional repression. Structural makeup and mechanisms by which multisubunit HDAC complexes recognize nucleosomes remain elusive. Our cryo–electron microscopy structures of the yeast class II HDAC ensembles show that the HDAC protomer comprises a triangle-shaped assembly of stoichiometry Hda12-Hda2-Hda3, in which the active sites of the Hda1 dimer are freely accessible. We also observe a tetramer of protomers, where the nucleosome binding modules are inaccessible. Structural analysis of the nucleosome-bound complexes indicates how positioning of Hda1 adjacent to histone H2B affords HDAC catalysis. Moreover, it reveals how an intricate network of multiple contacts between a dimer of protomers and the nucleosome creates a platform for expansion of the HDAC activities. Our study provides comprehensive insight into the structural plasticity of the HDAC complex and its functional mechanism of chromatin modification.

Electron transport pathways for the oxidation of endogenous substrate(s) in Acidithiobacillus ferrooxidans

2006 ◽  
Vol 52 (4) ◽  
pp. 317-327 ◽  
Author(s):  
Yongqiang Chen ◽  
Isamu Suzuki
Keyword(s):  
Electron Transport ◽  
Electron Acceptor ◽  
Acidithiobacillus Ferrooxidans ◽  
Complex I ◽  
Iron Chelators ◽  
Endogenous Respiration ◽  
Sugar Alcohols ◽  
Transport Pathways ◽  
Endogenous Substrate ◽  
Transport Inhibitors

Oxidation of endogenous substrate(s) of Acidithiobacillus ferrooxidans with O2 or Fe3+ as electron acceptor was studied in the presence of uncouplers and electron transport inhibitors. Endogenous substrate was oxidized with a respiratory quotient (CO2 produced/O2 consumed) of 1.0, indicating its carbohydrate nature. The oxidation was inhibited by complex I inhibitors (rotenone, amytal, and piericidin A) only partially, but piericidin A inhibited the oxidation with Fe3+ nearly completely. The oxidation was stimulated by uncouplers, and the stimulated activity was more sensitive to inhibition by complex I inhibitors. HQNO (2-heptyl-4-hydroxyquinoline N-oxide) also stimulated the oxidation, and the stimulated respiration was more sensitive to KCN inhibition than uncoupler stimulated respiration. Fructose, among 20 sugars and sugar alcohols including glucose and mannose, was oxidized with a CO2/O2 ratio of 1.0 by the organism. Iron chelators in general stimulated endogenous respiration, but some of them reduced Fe3+ chemically, introducing complications. The results are discussed in view of a branched electron transport system of the organism and its possible control.Key words: Acidithiobacillus ferrooxidans, endogenous respiration, uncouplers, electron transport.

Anode Biofilms ofGeoalkalibacter ferrihydriticusExhibit Electrochemical Signatures of Multiple Electron Transport Pathways

Langmuir ◽  
2015 ◽  
Vol 31 (45) ◽  
pp. 12552-12559 ◽  
Author(s):  
Rachel A. Yoho ◽  
Sudeep C. Popat ◽  
Laura Rago ◽  
Albert Guisasola ◽  
César I. Torres
Keyword(s):  
Electron Transport ◽  
Transport Pathways

scholarly journals Structural insights into the activation of human calcium-sensing receptor

2021 ◽  
Author(s):  
Xiaochen Chen ◽  
Lu Wang ◽  
Zhanyu Ding ◽  
Qianqian Cui ◽  
Li Han ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Large Scale ◽  
Transmembrane Domains ◽  
Structural Basis ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Cryo Electron Microscopy ◽  
Activation Mechanisms ◽  
G Protein Coupled ◽  
Structural Insights

AbstractHuman calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that maintains Ca2+ homeostasis in serum. Here, we present the cryo-electron microscopy structures of the CaSR in the inactive and active states. Complemented with previously reported crystal structures of CaSR extracellular domains, it suggests that there are three distinct conformations: inactive, intermediate and active state during the activation. We used a negative allosteric nanobody to stabilize the CaSR in the fully inactive state and found a new binding site for Ca2+ ion that acts as a composite agonist with L-amino acid to stabilize the closure of active Venus flytraps. Our data shows that the agonist binding leads to the compaction of the dimer, the proximity of the cysteine-rich domains, the large-scale transitions of 7-transmembrane domains, and the inter-and intrasubunit conformational changes of 7-transmembrane domains to accommodate the downstream transducers. Our results reveal the structural basis for activation mechanisms of the CaSR.

Structure of the maize photosystem I supercomplex with light-harvesting complexes I and II

Science ◽  
2018 ◽  
Vol 360 (6393) ◽  
pp. 1109-1113 ◽  
Author(s):  
Xiaowei Pan ◽  
Jun Ma ◽  
Xiaodong Su ◽  
Peng Cao ◽  
Wenrui Chang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Energy Transfer ◽  
Complex I ◽  
Light Harvesting ◽  
Light Conditions ◽  
Light Harvesting Complexes ◽  
Light Harvesting Complex ◽  
Cryo Electron Microscopy ◽  
Photosystems I And Ii ◽  
Light Harvesting Complex Ii

Plants regulate photosynthetic light harvesting to maintain balanced energy flux into photosystems I and II (PSI and PSII). Under light conditions favoring PSII excitation, the PSII antenna, light-harvesting complex II (LHCII), is phosphorylated and forms a supercomplex with PSI core and the PSI antenna, light-harvesting complex I (LHCI). Both LHCI and LHCII then transfer excitation energy to the PSI core. We report the structure of maize PSI-LHCI-LHCII solved by cryo–electron microscopy, revealing the recognition site between LHCII and PSI. The PSI subunits PsaN and PsaO are observed at the PSI-LHCI interface and the PSI-LHCII interface, respectively. Each subunit relays excitation to PSI core through a pair of chlorophyll molecules, thus revealing previously unseen paths for energy transfer between the antennas and the PSI core.

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