Rare-Earth Metalloligands for Low-Valent Cobalt Complexes: Fine Electronic Tuning via Co→RE Dative Interactions.

Rare-earth metalloligand supported low-valent cobalt complexes were synthesized by utilizing a small-sized heptadentate phosphinomethylamine LsNH3 and a large-sized arene-anchored hexadentate phosphinomethylamine LlArH3 ligand precursors. The RE(III)-Co(-I)-N2 (RE = Sc, Lu, Y, Gd, La) complexes containing rare-earth metals including the smallest Sc and largest La were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The Co(-I)→RE(III) dative interactions were all polarized with major contributions from the 3dz2 orbital of the cobalt center, which was slightly affected by the identity of rare-earth metalloligands. The IR spectroscopic data and redox potentials obtained from cyclic voltammetry revealed that the electronic property of the Co(-I) center was finely tuned by the rare-earth metalloligand, which was revealed by variation of the ligand systems containing LsN, LmN, and LlAr. Unlike the direct alteration of the electronic property of metal center via an ancillary ligand, such a series of rare-earth metalloligand represents a smooth strategy to tune the electronic property of transition metals.

A scandium metalloligand supported Ni(0) complex with a heterobimetallocycle: versatile reactivity with unsaturated bonds.

A N2-bridged tetranuclear Sc(III)-Ni(0) complex featuring a Ni → Sc interaction and a 4-membered [Sc-N-C-Ni] ring was synthesized and characterized. Bimetallic reactivity was demonstrated via reactions with a series of unsaturated compounds containing NC, CN, CC, CO and NN bonds.

ZIF-67-Derived Co/N-Doped Carbon-Functionalized MXene for Enhanced Electrochemical Sensing of Carbendazim.

Herein, ZIF-67-derived Co and N-doped carbon (Co/NC) particle-modified multilayer MXene (MXene@Co/NC) was developed as remarkable electrode material for carbendazim (CBZ) detection. MXene as a substrate provides an excellent conductive framework and plentiful accessibility sites. Co/NC particles embedding in MXene can not only prevent the interlayer stacking of MXene but also contribute a great deal of metal catalytic active sites and finally improve the adsorption and catalytic properties of the composite. Accordingly, the MXene@Co/NC electrode displays excellent electrocatalytic activity toward CBZ oxidation. Experimental parameters such as pH value, accumulation time, MXene@Co/NC modification volume and constituent materials' mass ratios were optimized. Under optimal conditions, the as-prepared sensor based on MXene@Co/NC holds a broad linearity range from 0.01 µM to 45.0 µM with a low limit of detection (LOD) of 3.3 nM (S/N = 3, S means the detection signal, while N represents the noise of the instrument). Moreover, the proposed sensor displays excellent anti-interference ability, superior reproducibility, excellent stability, and successfully achieves actual applications for CBZ detection in a lettuce sample.

Structural insights into the assembly and energy transfer of the Lhcb9-dependent photosystem I from moss Physcomitrium patens.

In plants and green algae, light-harvesting complexes I and II (LHCI and LHCII) constitute the antennae of photosystem I (PSI), thus effectively increasing the cross-section of the PSI core. The moss Physcomitrium patens (P. patens) represents a well-studied primary land-dwelling photosynthetic autotroph branching from the common ancestor of green algae and land plants at the early stage of evolution. P. patens possesses at least three types of PSI with different antenna sizes. The largest PSI form (PpPSI-L) exhibits a unique organization found neither in flowering plants nor in algae. Its formation is mediated by the P. patens-specific LHC protein, Lhcb9. While previous studies have revealed the overall architecture of PpPSI-L, its assembly details and the relationship between different PpPSI types remain unclear. Here we report the high-resolution structure of PpPSI-L. We identified 14 PSI core subunits, one Lhcb9, one phosphorylated LHCII trimer and eight LHCI monomers arranged as two belts. Our structural analysis established the essential role of Lhcb9 and the phosphorylated LHCII in stabilizing the complex. In addition, our results suggest that PpPSI switches between different types, which share identical modules. This feature may contribute to the dynamic adjustment of the light-harvesting capability of PSI under different light conditions.

Dynamic Regulation of the Light-Harvesting System through State Transitions in Land Plants and Green Algae.

Photosynthesis constitutes the only known natural process that captures the solar energy to convert carbon dioxide and water into biomass. The primary reactions of photosynthesis are catalyzed by the photosystem II (PSII) and photosystem I (PSI) complexes. Both photosystems associate with antennae complexes whose main function is to increase the light-harvesting capability of the core. In order to maintain optimal photosynthetic activity under a constantly changing natural light environment, plants and green algae regulate the absorbed photo-excitation energy between PSI and PSII through processes known as state transitions. State transitions represent a short-term light adaptation mechanism for balancing the energy distribution between the two photosystems by relocating light-harvesting complex II (LHCII) proteins. The preferential excitation of PSII (state 2) results in the activation of a chloroplast kinase which in turn phosphorylates LHCII, a process followed by the release of phosphorylated LHCII from PSII and its migration to PSI, thus forming the PSI-LHCI-LHCII supercomplex. The process is reversible, as LHCII is dephosphorylated and returns to PSII under the preferential excitation of PSI. In recent years, high-resolution structures of the PSI-LHCI-LHCII supercomplex from plants and green algae were reported. These structural data provide detailed information on the interacting patterns of phosphorylated LHCII with PSI and on the pigment arrangement in the supercomplex, which is critical for constructing the excitation energy transfer pathways and for a deeper understanding of the molecular mechanism of state transitions progress. In this review, we focus on the structural data of the state 2 supercomplex from plants and green algae and discuss the current state of knowledge concerning the interactions between antenna and the PSI core and the potential energy transfer pathways in these supercomplexes.

Structural, Spectroscopic, and Bonding Analyses of La(III)/Ce(III)-Tetrel Ate-Complexes.

In comparison with the research of transition-metal-tetrel complexes, the chemistry of lanthanide tetrel complexes, especially for these bearing heavier tetrel element ligands, is still relatively underexplored. In this research, K[Cp3Ln(III)CH2Ph], [(DME)3Li][Cp3Ln(III)GePh3], and [(DME)3Li][Cp3Ln(III)SnPh3] [Ln(III) = La(III), Ce(III)] have been synthesized by reacting [(DME)3Na][Cp3La(µ-Cl)LaCp3] or Cp3Ce(THF) with alkali metal alkyl, germyl, and stannyl reagents. Additionally, [(DME)3Li][Cp3Ce(III)SnPh3] is the first example of Ce(III)-Sn bond containing complex. All the obtained early Ln(III) tetrel ate-complexes were structurally analyzed by single-crystal X-ray diffraction. The formal shortness ratios of the Ln(III)-C, Ln(III)-Ge, and Ln(III)-Sn bonds are in the range of 1.03-1.11. Together with the previously reported [(DME)3Li][Cp3Ln(III)SiPh3], a group of tetrel (up to Sn) lanthanocene ate-complexes with an analogous coordination pattern are presented. Computational studies suggest the strongly polarized nature of the Ln(III)-E (E = C, Si, Ge, Sn) bonds in these complexes, with 77-85% atomic orbital contribution from tetrel elements and 15-23% atomic orbital contribution from Ln(III). The UV-vis measurements of this series of complexes show that the characteristic absorptions are hypsochromically shifted for Ln(III) heavier tetrel complexes in comparison to their lighter congeners. Moreover, the HOMOs, in which the Ln(III)-E σ-bonding orbitals are the dominant components, of these series complexes act as donor orbitals of the major electron transitions, as being disclosed by the time-dependent density functional theory analysis.

Dinitrogen Complexes of Cobalt(-I) Supported by Rare-Earth Metal-Based Metalloligands.

Sequential reactions of heptadentate phosphinoamine LH3 with rare-earth metal tris-alkyl precursor (Me3SiCH2)3Ln(THF)2 (Ln = Sc, Lu, Yb, Y, Gd) and a low-valent cobalt complex (Ph3P)3CoI afforded rare-earth metal-supported cobalt iodide complexes. Reduction of these iodide complexes under N2 allowed the isolation of the first series of dinitrogen complexes of Co(-I) featuring dative Co(-I) → Ln (Ln = Sc, Lu, Yb, Y, Gd) bonding interactions. These compounds were characterized by multinuclear NMR spectroscopy, X-ray diffraction analysis, electrochemistry, and computational studies. The correlation of N-N vibrational frequencies with the pKa of [Ln(H2O)6]3+ showed that strongest activation of N2 was achieved with the least Lewis acidic Gd(III) ion. Interestingly, these Ln-Co-N2 complexes catalyzed silylation of N2 in the presence of KC8 and Me3SiCl with turnover numbers (TONs) up to 16, where the lutetium-supported Co(-I) complex showed the highest activity within the series. The role of the Lewis acidic Ln(III) was crucial to achieve catalytic turnovers and tunable reactivity toward N2 functionalization.

Structural insights into photosynthetic cyclic electron transport.

During photosynthesis, light energy is utilized to drive sophisticated biochemical chains of electron transfers, converting solar energy into chemical energy that feeds most life on earth. Cyclic electron transfer/flow (CET/CEF) plays an essential role in efficient photosynthesis, as it balances the ATP/NADPH ratio required in various regulatory and metabolic pathways. Photosystem I, cytochrome b6f, and NADH dehydrogenase (NDH) are large multisubunit protein complexes embedded in the thylakoid membrane of the chloroplast and key players in NDH-dependent CEF pathway. Furthermore, small mobile electron carriers serve as shuttles for electrons between these membrane protein complexes. Efficient electron transfer requires transient interactions between these electron donors and acceptors. Structural biology has been a powerful tool to advance our knowledge of this important biological process. A number of structures of the membrane-embedded complexes, soluble electron carrier proteins, and transient complexes composed of both have now been determined. These structural data reveal detailed interacting patterns of these electron donor-acceptor pairs, thus allowing us to visualize the different parts of the electron transfer process. This review summarizes the current state of structural knowledge of three membrane complexes and their interaction patterns with mobile electron carrier proteins.

Responses of soil microbial communities to concentration gradients of antibiotic residues in typical greenhouse vegetable soils.

To explore the responses of soil microbial communities to concentration gradients of antibiotic residues in soil, 32 soil samples were collected from a typical greenhouse vegetable production base in Northern China in 2019. The total concentrations of 26 antibiotic residues in these soil samples was 83.24-4237.93 µg·kg-1, of which metabolites of tetracyclines were 23.34-1798.80 µg·kg-1. The total concentrations in 32 samples were clustered into three levels (L: <100 µg·kg-1, M: 100-300 µg·kg-1, H: >300 µg·kg-1) to elucidate the impacts of antibiotic residues on the diversity, structure, composition, function and antibiotic resistome of soil microbial community. Results showed that higher concentration of antibiotic residues in soil was prone to decrease the diversity and shift the structure and composition of soil microbial community. Antibiotic resistome occurred in soils with antibiotic residues exceeding 300 µg·kg-1. Interactions among soil bacteria followed the order of H > L > M, consistent with the relative abundances of mobile genetic elements. Bacteroidetes and Firmicutes were the top attributors impacting the profile of antibiotics in soil. According to weighted comprehensive pollution index of risk quotient, in 28.1 % of soil samples the residual antibiotics presented high ecological risk, whereas in the rest of soil samples the ecological risk is medium. The results will enrich the database and provide references for antibiotic contamination control in soils of the region and alike.

Early Lanthanide(III) Ate Complexes Featuring Ln-Si Bonds (Ln = La, Ce): Synthesis, Structural Characterization, and Bonding Analysis.

While research on lanthanide (Ln) complexes with silyl ligands is receiving growing attention, significantly unbalanced efforts have been devoted to different Ln elements. In comparison with the intense investigations on Ln elements such as Sm and Yb, the chemistry of silyl lanthanum and cerium complexes is much slower to develop, and no solid-state structure of a silyl lanthanum complex has been reported so far. In this research, four types of ate complexes, including [(DME)3Li][Cp3LnSi(H)Mes2], [(18-crown-6)K][Cp3LnSi(CH3)Ph2], [(DME)3Li][Cp3LnSiPh3], and [(12-crown-4)2Na] [Cp3LnSi(Ph)2Si(H)Ph2] (Ln = La, Ce), were synthesized by reacting [(DME)3Na][Cp3La(µ-Cl)LaCp3] or Cp3Ce(THF) with alkali metal silanides. All of the synthesized silyl Ln ate complexes were structurally characterized. La-Si bond lengths are in a range of 3.1733(4)-3.1897(10) Å, and the calculated formal shortness ratios of the La-Si bonds (1.071.08) are comparable to those in the reported silyl complexes having other Ln metal centers. The Ce-Si bond lengths (3.1415(6)-3.1705(9) Å) are within the typical range of reported silyl cerium ate complexes. 29Si solid-state NMR measurements on the diamagnetic silyl lanthanum complexes were conducted, and large one-bond hyperfine splitting constants arising from = 7/2) were resolved. Computational studies on these silyl lanthanum and cerium complexes suggested the polarized covalent feature of the Ln-Si bonds, which is in line with the measured large 1J139La-Si splitting constants.

Structural and Biochemical Analysis Reveals Catalytic Mechanism of Fucoidan Lyase from Flavobacterium sp. SA-0082.

Fucoidans represent a type of polyanionic fucose-containing sulfated polysaccharides (FCSPs) that are cleaved by fucoidan-degrading enzymes, producing low-molecular-weight fucoidans with multiple biological activities suitable for pharmacological use. Most of the reported fucoidan-degrading enzymes are glycoside hydrolases, which have been well studied for their structures and catalytic mechanisms. Little is known, however, about the rarer fucoidan lyases, primarily due to the lack of structural information. FdlA from Flavobacterium sp. SA-0082 is an endo-type fucoidan-degrading enzyme that cleaves the sulfated fuco-glucuronomannan (SFGM) through a lytic mechanism. Here, we report nine crystal structures of the catalytic N-terminal domain of FdlA (FdlA-NTD), in both its wild type (WT) and mutant forms, at resolutions ranging from 1.30 to 2.25 Å. We show that the FdlA-NTD adopts a right-handed parallel ß-helix fold, and possesses a substrate binding site composed of a long groove and a unique alkaline pocket. Our structural, biochemical, and enzymological analyses strongly suggest that FdlA-NTD utilizes catalytic residues different from other ß-helix polysaccharide lyases, potentially representing a novel polysaccharide lyase family.

Structure of Arabidopsis SOQ1 lumenal region unveils C-terminal domain essential for negative regulation of photoprotective qH.

Non-photochemical quenching (NPQ) plays an important role for phototrophs in decreasing photo-oxidative damage. qH is a sustained form of NPQ and depends on the plastid lipocalin (LCNP). A thylakoid membrane-anchored protein SUPPRESSOR OF QUENCHING1 (SOQ1) prevents qH formation by inhibiting LCNP. SOQ1 suppresses qH with its lumen-located thioredoxin (Trx)-like and NHL domains. Here we report structural data, genetic modification and biochemical characterization of Arabidopsis SOQ1 lumenal domains. Our results show that the Trx-like and NHL domains are associated together, with the cysteine motif located at their interface. Residue E859, required for SOQ1 function, is pivotal for maintaining the Trx-NHL association. Importantly, the C-terminal region of SOQ1 forms an independent ß-stranded domain that has structural homology to the N-terminal domain of bacterial disulfide bond protein D and is essential for negative regulation of qH. Furthermore, SOQ1 is susceptible to cleavage at the loops connecting the neighbouring lumenal domains both in vitro and in vivo, which could be a regulatory process for its suppression function of qH.

Supramolecular assembly of chloroplast NADH dehydrogenase-like complex with photosystem I from Arabidopsis thaliana.

Cyclic electron transport/flow (CET/CEF) in chloroplasts is a regulatory process essential for the optimization of plant photosynthetic efficiency. A crucial CEF pathway is catalyzed by a membrane-embedded NADH dehydrogenase-like (NDH) complex that contains at least 29 protein subunits and associates with photosystem I (PSI) to form the NDH-PSI supercomplex. Here, we report the 3.9 Å resolution structure of the Arabidopsis thaliana NDH-PSI (AtNDH-PSI) supercomplex. We constructed structural models for 26 AtNDH subunits, among which 11 are unique to chloroplasts and stabilize the core part of the NDH complex. In the supercomplex, one NDH can bind up to two PSI-light-harvesting complex I (PSI-LHCI) complexes at both sides of its membrane arm. Two minor LHCIs, Lhca5 and Lhca6, each present in one PSI-LHCI, interact with NDH and contribute to supercomplex formation and stabilization. Collectively, our study reveals the structural details of the AtNDH-PSI supercomplex assembly and provides a molecular basis for further investigation of the regulatory mechanism of CEF in plants.

Structural basis of LhcbM5-mediated state transitions in green algae.

In green algae and plants, state transitions serve as a short-term light-acclimation process in the regulation of the light-harvesting capacity of photosystems I and II (PSI and PSII, respectively). During the process, a portion of light-harvesting complex II (LHCII) is phosphorylated, dissociated from PSII and binds with PSI to form the supercomplex PSI-LHCI-LHCII. Here, we report high-resolution structures of PSI-LHCI-LHCII from Chlamydomonas reinhardtii, revealing the mechanism of assembly between the PSI-LHCI complex and two phosphorylated LHCII trimers containing all four types of LhcbM protein. 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 supercomplex formation. The results unravel the specific interactions and potential excitation energy transfer routes between green algal PSI and two phosphorylated LHCIIs.

Assembly of eukaryotic photosystem II with diverse light-harvesting antennas.

Photosystem II (PSII) catalyzes the light-driven oxygen-evolving reaction via its catalytic core and peripheral light-harvesting antennas. Oxyphototrophs have evolved diverse antenna systems, enabling them to adapt to different habitats. Recently, high-resolution structures of PSII-antenna supercomplexes from the green lineage (higher plants and green algae) and the red lineage (diatoms) were solved. The antenna complexes from the two lineages share similar protein folding, but differ in terms of the oligomeric states, pigment composition, and assembly patterns with the core. These differences result in distinct pigment-protein networks in PSII from different organisms. We herein summarize the similarities and differences in these structures and outline the molecular basis of the assembly, energy transfer, and regulation of the eukaryotic PSII-antenna supercomplexes.

Structural insights into catalytic mechanism and product delivery of cyanobacterial acyl-acyl carrier protein reductase.

Long-chain alk(a/e)nes represent the major constituents of conventional transportation fuels. Biosynthesis of alkanes is ubiquitous in many kinds of organisms. Cyanobacteria possess two enzymes, acyl-acyl carrier protein (acyl-ACP) reductase (AAR) and aldehyde-deformylating oxygenase (ADO), which function in a two-step alkane biosynthesis pathway. These two enzymes act in series and possibly form a complex that efficiently converts long chain fatty acyl-ACP/fatty acyl-CoA into hydrocarbon. While the structure of ADO has been previously described, structures of both AAR and AAR-ADO complex have not been solved, preventing deeper understanding of this pathway. Here, we report a ligand-free AAR structure, and three AAR-ADO complex structures in which AARs bind various ligands. Our results reveal the binding pattern of AAR with its substrate/cofactor, and suggest a potential aldehyde-transferring channel from AAR to ADO. Based on our structural and biochemical data, we proposed a model for the complete catalytic cycle of AAR.

Photosynthetic Phosphoribulokinase Structures: Enzymatic Mechanisms and the Redox Regulation of the Calvin-Benson-Bassham Cycle.

The Calvin-Benson-Bassham (CBB) cycle is responsible for CO2 assimilation and carbohydrate production in oxyphototrophs. Phosphoribulokinase (PRK) is an essential enzyme of the CBB cycle in photosynthesis, catalyzing ATP-dependent conversion of ribulose-5-phosphate (Ru5P) to ribulose-1,5-bisphosphate. The oxyphototrophic PRK is redox-regulated and can be further regulated by reversible association with both glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and oxidized chloroplast protein CP12. The resulting GAPDH/CP12/PRK complex is central in the regulation of the CBB cycle; however, the PRK-CP12 interface in the recently reported cyanobacterial GAPDH/CP12/PRK structure was not well resolved, and the detailed binding mode of PRK with ATP and Ru5P remains undetermined, as only apo-form structures of PRK are currently available. Here, we report the crystal structures of cyanobacterial (Synechococcus elongatus) PRK in complex with ADP and glucose-6-phosphate and of the Arabidopsis (Arabidopsis thaliana) GAPDH/CP12/PRK complex, providing detailed information regarding the active site of PRK and the key elements essential for PRK-CP12 interaction. Our structural and biochemical results together reveal that the ATP binding site is disrupted in the oxidized PRK, whereas the Ru5P binding site is occupied by oxidized CP12 in the GAPDH/CP12/PRK complex. This structure-function study greatly advances the understanding of the reaction mechanism of PRK and the subtle regulations of redox signaling for the CBB cycle.

Structural basis for electron transport mechanism of complex I-like photosynthetic NAD(P)H dehydrogenase.

NAD(P)H dehydrogenase-like (NDH) complex NDH-1L of cyanobacteria plays a crucial role in cyclic electron flow (CEF) around photosystem I and respiration processes. NDH-1L couples the electron transport from ferredoxin (Fd) to plastoquinone (PQ) and proton pumping from cytoplasm to the lumen that drives the ATP production. NDH-1L-dependent CEF increases the ATP/NADPH ratio, and is therefore pivotal for oxygenic phototrophs to function under stress. Here we report two structures of NDH-1L from Thermosynechococcus elongatus BP-1, in complex with one Fd and an endogenous PQ, respectively. Our structures represent the complete model of cyanobacterial NDH-1L, revealing the binding manner of NDH-1L with Fd and PQ, as well as the structural elements crucial for proper functioning of the NDH-1L complex. Together, our data provides deep insights into the electron transport from Fd to PQ, and its coupling with proton translocation in NDH-1L.

Structural analysis and comparison of light-harvesting complexes I and II.

Photosynthesis is a fundamental biological process involving the conversion of solar energy into chemical energy. The initial photochemical and photophysical events of photosynthesis are mediated by photosystem II (PSII) and photosystem I (PSI). Both PSII and PSI are multi-subunit supramolecular machineries composed of a core complex and a peripheral antenna system. The antenna system serves to capture light energy and transfer it to the core efficiently. Both PSII and PSI in the green lineage (plants and green algae) and PSI in red algae have an antenna system comprising a series of chlorophyll- and carotenoid-binding membrane proteins belonging to the light-harvesting complex (LHC) superfamily, including LHCII and LHCI. However, the antenna size and subunit composition vary considerably in the two photosystems from diverse organisms. On the basis of the plant and algal LHCII and LHCI structures that have been solved by X-ray crystallography and single-particle cryo-electron microscopy we review the detailed structural features and characteristic pigment properties of these LHCs in PSII and PSI. This article is part of a Special Issue entitled Light harvesting, edited by Dr. Roberta Croce.

miR-141-3p affects apoptosis and migration of endometrial stromal cells by targeting KLF-12.

Endometriosis is an estrogen-dependent disease that is characterized by pelvic pain and infertility. MicroRNAs have been shown to implicate in the progression of endometriosis. In our study, we used real-time PCR to evaluate the expression of miR-141-3p in endometrial samples. In addition, western blot analysis was used to assess the expression of Krüppel-like factor 12 (KLF-12). The proliferation and migration of ectopic endometrial stromal cells (ESCs) were determined by MTT assay and Transwell assay, respectively. Cell apoptosis was evaluated using a Cell Death Detection ELISA Plus kit. The results showed that miR-141-3p and KLF-12 were significantly different in paired ectopic and eutopic endometrial samples. miR-141-3p overexpression significantly restrained the proliferation and migration and promoted the apoptosis of ectopic ESCs, whereas a decreased level of miR-141-3p was associated with opposite results. Furthermore, dual-luciferase reporter assay confirmed that KLF-12 was a novel target of miR-141-3p, while it also decreased the effects of miR-141-3p on the proliferation, apoptosis, and migration of ectopic ESCs. Our data suggested that enhanced expression of miR-141-3p suppressed the proliferation and migration of ectopic ESCs and promoted their apoptosis via targeting KLF-12. Our results may provide a novel potential therapeutic target for the treatment of endometriosis.