scholarly journals Structural basis of LhcbM5-mediated state transitions in green algae

2021 ◽  
Author(s):  
Xiaowei Pan ◽  
Ryutaro Tokutsu ◽  
Anjie Li ◽  
Kenji Takizawa ◽  
Chihong Song ◽  
...  
Keyword(s):  
Green Algae ◽  
Light Harvesting ◽  
Excitation Energy Transfer ◽  
Structural Basis ◽  
State Transitions ◽  
Light Harvesting Complexes ◽  
Functional Studies ◽  
Amino Terminal ◽  
Green Algal ◽  
Mutant Strains

AbstractIn green algae and plants, state transitions serve as a short-term light acclimation process to regulate light harvesting capacity of photosystems I and II (PSI and PSII). During the process, a portion of the light-harvesting complexes II (LHCII) are phosphorylated, dissociate from PSII and bind PSI to form PSI-LHCI-LHCII supercomplex. Here we report high-resolution structures of PSI-LHCI-LHCII supercomplex from Chlamydomonas reinhardtii, revealing the mechanism of assembly between PSI-LHCI complex and two phosphorylated LHCII trimers containing all four types of LhcbM proteins. Two specific LhcbM isoforms, namely LhcbM1 and LhcbM5, directly interact with the PSI core through their phosphorylated amino-terminal regions. Furthermore, biochemical and functional studies on mutant strains lacking either LhcbM1 or LhcbM5 indicate that only LhcbM5 is indispensable in the supercomplex formation. The results unraveled the specific interactions and potential excitation energy transfer routes between green algal PSI and two phosphorylated LHCIIs.

scholarly journals Trimeric Photosystem I facilitates energy transfer from phycobilisomes in Synechocystis PCC 6803

2021 ◽  
Author(s):  
Parveen Akhtar ◽  
Avratanu Biswas ◽  
Fanny Balog-Vig ◽  
Ildiko Domonkos ◽  
László Kovács ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Light Harvesting ◽  
Excitation Energy Transfer ◽  
State Transitions ◽  
Synechocystis Pcc 6803 ◽  
Light Harvesting Complexes ◽  
Time Resolved ◽  
Cyanobacterial Species ◽  
In Cells ◽  
Pcc 6803

In cyanobacteria, phycobilisomes serve as peripheral light-harvesting complexes of the two photosystems, extending their antenna size and the wavelength range of photons available for photosynthesis. The abundance of phycobilisomes, the number of phycobiliproteins they contain, and their light-harvesting function are dynamically adjusted in response to the physiological conditions. Phycobilisomes are also thought to be involved in state transitions that maintain the excitation balance between the two photosystems. Unlike its eukaryotic counterpart, PSI is trimeric in many cyanobacterial species and the physiological significance of this is not well understood. Here we compared the composition and light-harvesting function of phycobilisomes in cells of Synechocystis PCC 6803, which has primarily trimeric PSI, and the ?psaL mutant unable to form trimers. We also investigated a mutant additionally lacking the PsaJ and PsaF subunits of PSI, as PsaF has been proposed to facilitate interaction with phycobilisomes. Both strains with monomeric PSI accumulated significantly less phycocyanin (which constitutes the phycobilisome rods) per chlorophyll, while the allophycocyanin content was unchanged compared to WT. These data show that cells with monomeric PSI have higher abundance of smaller phycobilisomes. Steady-state and time-resolved fluorescence spectroscopy at room temperature and 77 K revealed that PSII receives more energy from the phycobilisomes at the expense of PSI in cells with monomeric PSI, regardless of the presence of PsaF. Taken together, these results show that the trimeric organization of PSI is advantageous for efficient and balanced excitation energy transfer from phycobilisomes in Synechocystis.

scholarly journals Structural basis of LhcbM5-mediated state transitions in green algae

Nature Plants ◽  
2021 ◽  
Author(s):  
Xiaowei Pan ◽  
Ryutaro Tokutsu ◽  
Anjie Li ◽  
Kenji Takizawa ◽  
Chihong Song ◽  
...  
Keyword(s):  
Green Algae ◽  
Structural Basis ◽  
State Transitions

scholarly journals Structural basis for allosteric transitions of a multidomain pentameric ligand-gated ion channel

2020 ◽  
Vol 117 (24) ◽  
pp. 13437-13446 ◽  
Author(s):  
Haidai Hu ◽  
Rebecca J. Howard ◽  
Ugo Bastolla ◽  
Erik Lindahl ◽  
Marc Delarue
Keyword(s):  
Ion Channels ◽  
Normal Mode Analysis ◽  
Mode Analysis ◽  
Structural Basis ◽  
State Transitions ◽  
Amino Terminal ◽  
Subunit Interface ◽  
High Resolution Structure ◽  
Electrochemical Signal ◽  
Multiple Conformations

Pentameric ligand-gated ion channels (pLGICs) are allosteric receptors that mediate rapid electrochemical signal transduction in the animal nervous system through the opening of an ion pore upon binding of neurotransmitters. Orthologs have been found and characterized in prokaryotes and they display highly similar structure–function relationships to eukaryotic pLGICs; however, they often encode greater architectural diversity involving additional amino-terminal domains (NTDs). Here we report structural, functional, and normal-mode analysis of two conformational states of a multidomain pLGIC, called DeCLIC, from aDesulfofustisdeltaproteobacterium, including a periplasmic NTD fused to the conventional ligand-binding domain (LBD). X-ray structure determination revealed an NTD consisting of two jelly-roll domains interacting across each subunit interface. Binding of Ca2+at the LBD subunit interface was associated with a closed transmembrane pore, with resolved monovalent cations intracellular to the hydrophobic gate. Accordingly, DeCLIC-injected oocytes conducted currents only upon depletion of extracellular Ca2+; these were insensitive to quaternary ammonium block. Furthermore, DeCLIC crystallized in the absence of Ca2+with a wide-open pore and remodeled periplasmic domains, including increased contacts between the NTD and classic LBD agonist-binding sites. Functional, structural, and dynamical properties of DeCLIC paralleled those of sTeLIC, a pLGIC from another symbiotic prokaryote. Based on these DeCLIC structures, we would reclassify the previous structure of bacterial ELIC (the first high-resolution structure of a pLGIC) as a “locally closed” conformation. Taken together, structures of DeCLIC in multiple conformations illustrate dramatic conformational state transitions and diverse regulatory mechanisms available to ion channels in pLGICs, particularly involving Ca2+modulation and periplasmic NTDs.

Variety, the spice of life and essential for robustness in excitation energy transfer in light-harvesting complexes

2020 ◽  
Vol 221 ◽  
pp. 59-76 ◽  
Author(s):  
Sue Ann Oh ◽  
David F. Coker ◽  
David A. W. Hutchinson
Keyword(s):  
Energy Transfer ◽  
Excitation Energy ◽  
Recent Work ◽  
Energy Transport ◽  
Light Harvesting ◽  
Excitation Energy Transfer ◽  
Light Harvesting Complexes ◽  
Protein Scaffold ◽  
Site Variation

We review our recent work showing how important the site-to-site variation in coupling between chloroplasts in FMO and their protein scaffold environment is for energy transport in FMO and investigate the role of vibronic modes in this transport.

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