Three-Dimensional Reconstruction of Icosahedral Virus by Symmetry-Adapted Functions

A three-dimensional （3D） reconstruction of icosahedral virus is carried out by the icosahedral symmetry-adapted function （ISAF） method in spherical coordinates. In order to reduce the influence of noise, it is better to use the basis functions that have identical symmetry with the object reconstructed. It is verified that the ISAF method has stronger ability to reduce the influence of noise to grain the resolution better than that of the conventional method by the simulation of 3D reconstruction.

Structural and spectroscopic insights into fucoxanthin chlorophyll a/c-binding proteins of diatoms in diverse oligomeric states

Diatoms,a group of prevalent marine algae,contribute significantly to global primary productivity.Their substantial biomass is linked to enhanced absorption of blue-green light underwater,facilitated by fucoxanthin chlorophyll(Chl)a/c-binding proteins(FCPs),which exhibit oligomeric diversity across diatom species.Using mild clear native PAGE analysis of solubilized thylakoid membranes,we displayed monomeric,dimeric,trimeric,tetrameric,and pentameric FCPs in diatoms.Mass spectrometry analysis revealed that each oligomeric FCP has a specific protein composition,and together they constitute a large Lhcf family of FCP antennas.In addition,we resolved the structures of the Thalassiosira pseudonana FCP(Tp-FCP)homotrimer and the Chaetoceros gracilis FCP(Cg-FCP)pentamer by cryoelectron microscopy at 2.73-Åand 2.65-Åresolution,respectively.The distinct pigment compositions and organizations of various oligomeric FCPs affect their blue-green light-harvesting,excitation energy transfer pathways.Compared with dimeric and trimeric FCPs,the Cg-FCP tetramer and Cg-FCP pentamer exhibit stronger absorption by Chl c,redshifted and broader Chl a fluorescence emission,and more robust circular dichroism signals originating from Chl a-carotenoid dimers.These spectroscopic characteristics indicate that Chl a molecules in the Cg-FCP tetramer and Cg-FCP pentamer are more heterogeneous than in both dimers and the Tp-FCP trimer.The structural and spectroscopic insights provided by this study contribute to a better understanding of the mechanisms that empower diatoms to adapt to fluctuating light environments.

A unique photosystem I reaction center from a chlorophyll d-containing cyanobacterium Acaryochloris marina

Photosystem I(PSI)is a large protein supercomplex that catalyzes the light-dependent oxidation of plastocyanin(or cytochrome c6)and the reduction of ferredoxin.This catalytic reaction is realized by a transmembrane electron transfer chain consisting of primary electron donor(a special chlorophyll(Chl)pair)and electron acceptors A_(0),A_(1),and three Fe_(4)S_(4) clusters,F_(X),F_(A),and F_(B).Here we report the PSI structure from a Chl d-dominated cyanobacterium Acaryochloris marina at 3.3Åresolution obtained by single-particle cryo-electron microscopy.The A.marina PSI exists as a trimer with three identical monomers.Surprisingly,the structure reveals a unique composition of electron transfer chain in which the primary electron acceptor A_(0) is composed of two pheophytin a rather than Chl a found in any other well-known PSI structures.A novel subunit Psa27 is observed in the A.marina PSI structure.In addition,77 Chls,13α-carotenes,two phylloquinones,three Fe-S clusters,two phosphatidyl glycerols,and one monogalactosyl-diglyceride were identified in each PSI monomer.Our results provide a structural basis for deciphering the mechanism of photosynthesis in a PSI complex with Chl d as the dominating pigments and absorbing far-red light.