Under natural environments,plants and algae have evolved various photosynthetic acclimation mechanisms in response to the constantly changing light conditions.The state transition and long-term response processes in photosynthetic acclimation involve remodeling and composition alteration of thylakoid membrane.A chloroplast protein kinase named Stt7/STN7 has been found to have pivotal roles in both state transition and longterm response.Here we report the crystal structures of the kinase domain of a putative Stt7/STN7 homolog from Micromonas sp.RCC299(MsStt7d)in the apo form and in complex with various nucleotide substrates.MsStt7d adopts a canonical protein kinase fold and contains all the essential residues at the active site.A novel hairpin motif,found to be a conserved feature of the Stt7/STN7 family and indispensable for the kinase stability,interacts with the activation loop and fi xes it in an active conformation.We have also demonstrated that MsStt7d is a dualspecifi city kinase that phosphorylates both Thr and Tyr residues.Moreover,preliminary in vitro data suggest that it might be capable of phosphorylating a consensus N-terminal pentapeptide of light-harvesting proteins Micromonas Lhcp4 and Arabidopsis Lhcb1 directly.The potential peptide/protein substrate binding site is predicted based on the location of a pseudo-substrate contributed by the adjacent molecule within the crystallographic dimer.The structural and biochemical data presented here provide a framework for an improved understanding on the role of Stt7/STN7 in photosynthetic acclimation.
Jiangtao GuoXuepeng WeiMei LiXiaowei PanWenrui ChangZhenfeng Liu
Dear Editor, The methylation modifications of histone 3 lysine 4 （H3K4） have essential effects on biological processes including gene expression and transcription, cell cycle progression, and DNA repair. From yeast to mammals, the SET1 and MLL-like （mixed-lineage leukemia） multi-subunit protein complexes, known as SET1 or MLL COMPASS （Schneider et al., 2005）, are responsible for H3K4 methylation. In addition to the catalytic SET domain, the SET1 and MLL COMPASS complexes also contain a number of conserved subunits including WDR5 （Cps30）, RbBP5 （Cps50）.
In addition to DNA repair pathways,cells utilize translesion DNA synthesis(TLS)to bypass DNA lesions during replication.During TLS,Y-family DNA polymerase(Polη,Polκ,Polιand Rev1)inserts specific nucleotide opposite preferred DNA lesions,and then Polζ consisting of two subunits,Rev3 and Rev7,carries out primer extension.Here,we report the complex structures of Rev3-Rev7-Rev1^(CTD) and Rev3-Rev7-Rev1^(CTD)-Polκ^(RIR).These two structures demonstrate that Rev1^(CTD) contains separate binding sites for Polκand Rev7.Our BIAcore experiments provide additional support for the notion that the interaction between Rev3 and Rev7 increases the affinity of Rev7 and Rev1.We also verified through FRET experiment that Rev1,Rev3,Rev7 and Polκ form a stable quaternary complex in vivo,thereby suggesting an efficient switching mechanism where the“inserter”polymerase can be immediately replaced by an“extender”polymerase within the same quaternary complex.
The mitochondrial respiratory complex Ⅱ or succinate:ubiquinone oxidoreductase(SQR)is a key membrane complex in both the tricarboxylic acid cycle and aerobic respiration.Five disinfectant compounds were investigated with their potent inhibition effects on the ubiquinone reduction activity of the porcine mitochondrial SQR by enzymatic assay and crystallography.Crystal structure of the SQR bound with thiabendazole(TBZ)reveals a different inhibitor-binding feature at the ubiquinone binding site where a water molecule plays an important role.The obvious inhibitory effect of TBZ based on the biochemical data(IC50~100μmol/L)and the significant structure-based binding affinity calculation(~94μmol/L)draw the suspicion of using TBZ as a good disinfectant compound for nematode infections treatment and fruit storage.
Qiangjun ZhouYujia ZhaiJizhong LouMan LiuXiaoyun PangFei Sun
In this review we summarize the progress made towards understanding the role of protein-protein interactions in the function of various bioluminescence systems of marine organisms,including bacteria,jellyfish and soft corals,with particular focus on methodology used to detect and characterize these interactions.In some bioluminescence systems,protein-protein interactions involve an“accessory protein”whereby a stored substrate is efficiently delivered to the bioluminescent enzyme luciferase.Other types of complexation mediate energy transfer to an“antenna protein”altering the color and quantum yield of a bioluminescence reaction.Spatial structures of the complexes reveal an important role of electrostatic forces in governing the corresponding weak interactions and define the nature of the interaction surfaces.The most reliable structural model is available for the protein-protein complex of the Ca2+-regulated photoprotein clytin and green-fluorescent protein(GFP)from the jellyfish Clytia gregaria,solved by means of Xray crystallography,NMR mapping and molecular docking.This provides an example of the potential strategies in studying the transient complexes involved in bioluminescence.It is emphasized that structural studies such as these can provide valuable insight into the detailed mechanism of bioluminescence.
Maxim S.TitushinYingang FengJohn LeeEugene S.VysotskiZhi-Jie Liu
The Mn cluster （Mn4CaO5） on the thylakoid luminal side of photosystem II （PSII） catalyzes the photosynthetic oxygen-evolving reaction, an essential process for life on Earth. In higher plants and green algae, the Mn cluster is surrounded by the membraneextrinsic proteins PsbO （33 kDa）, PsbP （23 kDa）, and PsbQ （17 kDa） （Murata and Miyao, 1985）.
