Molecular structure and characterization of the Thermochromatium tepidum light-harvesting 1 photocomplex produced in a foreign host.

Purple phototrophic bacteria possess light-harvesting 1 and reaction center (LH1-RC) core complexes that play a key role in converting solar energy to chemical energy. High-resolution structures of LH1-RC and RC complexes have been intensively studied and have yielded critical insight into the architecture and interactions of their proteins, pigments, and cofactors. Nevertheless, a detailed picture of the structure and assembly of LH1-only complexes is lacking due to the intimate association between LH1 and the RC. To study the intrinsic properties and structure of an LH1-only complex, a genetic system was constructed to express the Thermochromatium (Tch.) tepidum LH1 complex heterologously in a modified Rhodospirillum rubrum mutant strain. The heterologously expressed Tch. tepidum LH1 complex was isolated in a pure form free of the RC and exhibited the characteristic absorption properties of Tch. tepidum. Cryo-EM structures of the LH1-only complexes revealed a closed circular ring consisting of either 14 or 15 αß-subunits, making it the smallest completely closed LH1 complex discovered thus far. Surprisingly, the Tch. tepidum LH1-only complex displayed even higher thermostability than that of the native LH1-RC complex. These results reveal previously unsuspected plasticity of the LH1 complex, provide new insights into the structure and assembly of the LH1-RC complex, and show how molecular genetics can be exploited to study membrane proteins from phototrophic organisms whose genetic manipulation is not yet possible.

Therapeutic effect of ginkgetin on smoke-induced airway inflammation by down-regulating the c/EBPß signaling pathway and CCL2 expression.

ETHNOPHARMACOLOGICAL RELEVANCE: Ginkgo biloba leaf and seed have been traditionally used in ancient China for the treatment of cough and asthma. However, there is limited literature available on the anti-COPD effects and mechanisms of Ginkgo biloba. AIMS OF THE STUDY: The aim of this study was to comprehensively investigate the therapeutic potential of ginkgo extracts in COPD through a combination of in vivo and in vitro functional experiments. Transcriptomic analyses were also employed to uncover novel molecular mechanisms underlying the therapeutic effects of ginkgetin in COPD. MATERIALS AND METHODS: The therapeutic efficacy of ginkgo extracts was assessed in a COPD model. The anti-inflammatory effects of ginkgetin and its underlying molecular mechanisms were examined in A549 cells treated with cigarette smoke extract (CSE). Additionally, transcriptomic analyses were conducted to identify novel molecular pathways influenced by ginkgetin. These findings were further validated using quantitative real-time polymerase chain reaction (qPCR) and Western blot techniques. RESULTS: The ethyl acetate extract of Ginkgo biloba L. seeds and ginkgetin treatment significantly reduced cytokine production in COPD mice. Following drug administration, lung function improved in different groups. The transcriptome data strongly supports the inhibitory effect of ginkgetin on CSE-induced inflammation through the downregulation of the c/EBPß signaling pathway and subsequent inhibition of CCL2 expression. CONCLUSION: Our results demonstrate that ginkgetin, one of the biflavones found in Ginkgo biloba, exhibits inhibitory effects on smoke-induced airway inflammation. This effect is achieved through the downregulation of the c/EBPß signaling pathway and the reduction of CCL2 expression.

Light-Quality-Adapted Carotenoid Photoprotection in the Photosystem of Roseiflexus castenholzii.

The photosystem of filamentous anoxygenic phototroph Roseiflexus (Rfl.) castenholzii comprises a light-harvesting (LH) complex encircling a reaction center (RC), which intensely absorbs blue-green light by carotenoid (Car) and near-infrared light by bacteriochlorophyll (BChl). To explore the influence of light quality (color) on the photosynthetic activity, we compared the pigment compositions and triplet excitation dynamics of the LH-RCs from Rfl. castenholzii was adapted to blue-green light (bg-LH-RC) and to near-infrared light (nir-LH-RC). Both LH-RCs bind γ-carotene derivatives; however, compared to that of nir-LH-RC (12%), bg-LH-RC contains substantially higher keto-γ-carotene content (43%) and shows considerably faster BChl-to-Car triplet excitation transfer (10.9 ns vs 15.0 ns). For bg-LH-RC, but not nir-LH-RC, selective photoexcitation of Car and the 800 nm-absorbing BChl led to Car-to-Car triplet transfer and BChl-Car singlet fission reactions, respectively. The unique excitation dynamics of bg-LH-RC enhances its photoprotection, which is crucial for the survival of aquatic anoxygenic phototrophs from photooxidative stress.

Energy Transfer and Exciton Relaxation in B880-B800-RC Complex through Two-Dimensional Electronic Spectroscopy.

The light-harvesting (LH) and reaction center (RC) core complex of purple bacterium Roseiflexus castenholzii, B880-B800-RC, are different from those of the typical photosynthetic unit, (B850-B800)x-B880-RC. To investigate the excitation flowing dynamics in this unique complex, two-dimensional electronic spectroscopy is employed. The obtained time constants for the exciton relaxation in B880, exciton relaxation in B800, B800 → B880 energy transfer (EET), and B880 → closed RC EET are 43 fs, 177 fs, 1.9 ps, and 205 ps, respectively. These time constants result in an overall EET efficiency similar to that of the typical photosynthetic unit. Analysis of the oscillatory signals reveals that while several vibronic coherences are involved in the exciton relaxation process, only one prominent vibronic coherence, with a frequency of 27 cm-1 and coupled to the B880 electronic transition, may contribute to the B800 → B880 EET process.

Structural insights into the unusual core photocomplex from a triply extremophilic purple bacterium, Halorhodospira halochloris.

Halorhodospira (Hlr.) halochloris is a triply extremophilic phototrophic purple sulfur bacterium, as it is thermophilic, alkaliphilic, and extremely halophilic. The light-harvesting-reaction center (LH1-RC) core complex of this bacterium displays an LH1-Qy transition at 1,016 nm, which is the lowest-energy wavelength absorption among all known phototrophs. Here we report the cryo-EM structure of the LH1-RC at 2.42 Å resolution. The LH1 complex forms a tricyclic ring structure composed of 16 αßγ-polypeptides and one αß-heterodimer around the RC. From the cryo-EM density map, two previously unrecognized integral membrane proteins, referred to as protein G and protein Q, were identified. Both of these proteins are single transmembrane-spanning helices located between the LH1 ring and the RC L-subunit and are absent from the LH1-RC complexes of all other purple bacteria of which the structures have been determined so far. Besides bacteriochlorophyll b molecules (B1020) located on the periplasmic side of the Hlr. halochloris membrane, there are also two arrays of bacteriochlorophyll b molecules (B800 and B820) located on the cytoplasmic side. Only a single copy of a carotenoid (lycopene) was resolved in the Hlr. halochloris LH1-α3ß3 and this was positioned within the complex. The potential quinone channel should be the space between the LH1-α3ß3 that accommodates the single lycopene but does not contain a γ-polypeptide, B800 and B820. Our results provide a structural explanation for the unusual Qy red shift and carotenoid absorption in the Hlr. halochloris spectrum and reveal new insights into photosynthetic mechanisms employed by a species that thrives under the harshest conditions of any phototrophic microorganism known.

Microbial metabolism of diosgenin by a novel isolated Mycolicibacterium sp. HK-90: A promising biosynthetic platform to produce 19-carbon and 21-carbon steroids.

Green manufacture of steroid precursors from diosgenin by microbial replacing multistep chemical synthesis has been elusive. It is currently limited by the lack of strain and degradation mechanisms. Here, we demonstrated the feasibility of this process using a novel strain Mycolicibacterium sp. HK-90 with efficiency in diosgenin degradation. Diosgenin degradation by strain HK-90 involves the selective removal of 5,6-spiroketal structure, followed by the oxygenolytic cleavage of steroid nuclei. Bioinformatic analyses revealed the presence of two complete steroid catabolic gene clusters, SCG-1 and SCG-2, in the genome of strain HK-90. SCG-1 cluster was found to be involved in classic phytosterols or cholesterol catabolic pathway through the deletion of key kstD1 gene, which promoted the mutant m-∆kstD1 converting phytosterols to intermediate 9α-hydroxyandrostenedione (9-OHAD). Most impressively, global transcriptomics and characterization of key genes suggested SCG-2 as a potential gene cluster encoding diosgenin degradation. The gene inactivation of kstD2 in SCG-2 resulted in the conversion of diosgenin to 9-OHAD and 9,16-dihydroxy-pregn-4-ene-3,20-dione (9,16-(OH)2 -PG) in mutant m-ΔkstD2. Moreover, the engineered strain mHust-ΔkstD1,2,3 with a triple deletion of kstDs was constructed, which can stably accumulate 9-OHAD by metabolizing phytosterols, and accumulate 9-OHAD and 9,16-(OH)2 -PG from diosgenin. Diosgenin catabolism in strain mHust-ΔkstD1,2,3 was revealed as a progression through diosgenone, 9,16-(OH)2 -PG, and 9-OHAD to 9α-hydroxytestosterone (9-OHTS). So far, this work is the first report on genetically engineered strain metabolizing diosgenin to produce 21-carbon and 19-carbon steroids. This study presents a promising biosynthetic platform for the green production of steroid precursors, and provide insights into the complex biochemical mechanism of diosgenin catabolism.

Structures and organizations of PSI-AcpPCI supercomplexes from red tidal and coral symbiotic photosynthetic dinoflagellates.

Marine photosynthetic dinoflagellates are a group of successful phytoplankton that can form red tides in the ocean and also symbiosis with corals. These features are closely related to the photosynthetic properties of dinoflagellates. We report here three structures of photosystem I (PSI)-chlorophylls (Chls) a/c-peridinin protein complex (PSI-AcpPCI) from two species of dinoflagellates by single-particle cryoelectron microscopy. The crucial PsaA/B subunits of a red tidal dinoflagellate Amphidinium carterae are remarkably smaller and hence losing over 20 pigment-binding sites, whereas its PsaD/F/I/J/L/M/R subunits are larger and coordinate some additional pigment sites compared to other eukaryotic photosynthetic organisms, which may compensate for the smaller PsaA/B subunits. Similar modifications are observed in a coral symbiotic dinoflagellate Symbiodinium species, where two additional core proteins and fewer AcpPCIs are identified in the PSI-AcpPCI supercomplex. The antenna proteins AcpPCIs in dinoflagellates developed some loops and pigment sites as a result to accommodate the changed PSI core, therefore the structures of PSI-AcpPCI supercomplex of dinoflagellates reveal an unusual protein assembly pattern. A huge pigment network comprising Chls a and c and various carotenoids is revealed from the structural analysis, which provides the basis for our deeper understanding of the energy transfer and dissipation within the PSI-AcpPCI supercomplex, as well as the evolution of photosynthetic organisms.

High-resolution structure and biochemical properties of the LH1-RC photocomplex from the model purple sulfur bacterium, Allochromatium vinosum.

The mesophilic purple sulfur phototrophic bacterium Allochromatium (Alc.) vinosum (bacterial family Chromatiaceae) has been a favored model for studies of bacterial photosynthesis and sulfur metabolism, and its core light-harvesting (LH1) complex has been a focus of numerous studies of photosynthetic light reactions. However, despite intense efforts, no high-resolution structure and thorough biochemical analysis of the Alc. vinosum LH1 complex have been reported. Here we present cryo-EM structures of the Alc. vinosum LH1 complex associated with reaction center (RC) at 2.24 Å resolution. The overall structure of the Alc. vinosum LH1 resembles that of its moderately thermophilic relative Alc. tepidum in that it contains multiple pigment-binding α- and ß-polypeptides. Unexpectedly, however, six Ca ions were identified in the Alc. vinosum LH1 bound to certain α1/ß1- or α1/ß3-polypeptides through a different Ca2+-binding motif from that seen in Alc. tepidum and other Chromatiaceae that contain Ca2+-bound LH1 complexes. Two water molecules were identified as additional Ca2+-coordinating ligands. Based on these results, we reexamined biochemical and spectroscopic properties of the Alc. vinosum LH1-RC. While modest but distinct effects of Ca2+ were detected in the absorption spectrum of the Alc. vinosum LH1 complex, a marked decrease in thermostability of its LH1-RC complex was observed upon removal of Ca2+. The presence of Ca2+ in the photocomplex of Alc. vinosum suggests that Ca2+-binding to LH1 complexes may be a common adaptation in species of Chromatiaceae for conferring spectral and thermal flexibility on this key component of their photosynthetic machinery.

Multi-point immobilization of GH 11 endo-ß-1,4-xylanase on magnetic MOF composites for higher yield of xylo-oligosaccharides.

GH 11 endo-ß-1,4-xylanase (Xy) was a crucial enzyme for xylooligosaccharides (XOS) production. The lower reusability and higher cost of purification has limited the industrial application of Xy. Addressing these challenges, our study utilized various immobilization techniques, different supports and forces for Xy immobilization. This study presents a new method in the development of Fe3O4@PDA@MOF-Xy which is immobilized via multi-point interaction forces, demonstrating a significant advancement in protein loading capacity (80.67 mg/g), and exhibiting remarkable tolerance to acidic and alkaline conditions. This method significantly improved Xy reusability and efficiency for industrial applications, maintaining 60 % activity over 10 cycles. Approximately 23 % XOS production was achieved by Fe3O4@PDA@MOF-Xy. Moreover, the yield of XOS from cobcorn xylan using this system was 1.15 times higher than that of the free enzyme system. These results provide a theoretical and applicative basis for enzyme immobilization and XOS industrial production.

Oxygen-evolving photosystem II structures during S1-S2-S3 transitions.

Photosystem II (PSII) catalyses the oxidation of water through a four-step cycle of Si states (i = 0-4) at the Mn4CaO5 cluster1-3, during which an extra oxygen (O6) is incorporated at the S3 state to form a possible dioxygen4-7. Structural changes of the metal cluster and its environment during the S-state transitions have been studied on the microsecond timescale. Here we use pump-probe serial femtosecond crystallography to reveal the structural dynamics of PSII from nanoseconds to milliseconds after illumination with one flash (1F) or two flashes (2F). YZ, a tyrosine residue that connects the reaction centre P680 and the Mn4CaO5 cluster, showed structural changes on a nanosecond timescale, as did its surrounding amino acid residues and water molecules, reflecting the fast transfer of electrons and protons after flash illumination. Notably, one water molecule emerged in the vicinity of Glu189 of the D1 subunit of PSII (D1-E189), and was bound to the Ca2+ ion on a sub-microsecond timescale after 2F illumination. This water molecule disappeared later with the concomitant increase of O6, suggesting that it is the origin of O6. We also observed concerted movements of water molecules in the O1, O4 and Cl-1 channels and their surrounding amino acid residues to complete the sequence of electron transfer, proton release and substrate water delivery. These results provide crucial insights into the structural dynamics of PSII during S-state transitions as well as O-O bond formation.

Structural insights into photosystem II supercomplex and trimeric FCP antennae of a centric diatom Cyclotella meneghiniana.

Diatoms are dominant marine algae and contribute around a quarter of global primary productivity, the success of which is largely attributed to their photosynthetic capacity aided by specific fucoxanthin chlorophyll-binding proteins (FCPs) to enhance the blue-green light absorption under water. We purified a photosystem II (PSII)-FCPII supercomplex and a trimeric FCP from Cyclotella meneghiniana (Cm) and solved their structures by cryo-electron microscopy (cryo-EM). The structures reveal detailed organizations of monomeric, dimeric and trimeric FCP antennae, as well as distinct assemblies of Lhcx6_1 and dimeric FCPII-H in PSII core. Each Cm-PSII-FCPII monomer contains an Lhcx6_1, an FCP heterodimer and other three FCP monomers, which form an efficient pigment network for harvesting energy. More diadinoxanthins and diatoxanthins are found in FCPs, which may function to quench excess energy. The trimeric FCP contains more chlorophylls c and fucoxanthins. These diversified FCPs and PSII-FCPII provide a structural basis for efficient light energy harvesting, transfer, and dissipation in C. meneghiniana.

Carotenoid-Mediated Long-Range Energy Transfer in the Light Harvesting-Reaction Center Complex from Photosynthetic Bacterium Roseiflexus castenholzii.

The light harvesting-reaction center complex (LH-RC) of Roseiflexus castenholzii binds bacteriochlorophylls a (BChls a), B800 and B880, absorbing around 800 and 880 nm, respectively. We comparatively investigated the interband excitation energy transfer (EET) dynamics of the wild-type LH-RC (wt-LH-RC) of Rfl. castenholzii and its carotenoid (Car)-less mutant (m-LH-RC) and found that Car can boost the B800 → B880 EET rate from (2.43 ps)-1 to (1.75 ps)-1, accounting for 38% acceleration of the EET process. Interestingly, photoexcitation of wt-LH-RC at 800 nm induced pronounced excitation dynamics of Car despite the insufficient photon energy for direct Car excitation, a phenomenon which is attributed to the BChl-Car exciplex 1[B800(↑↑)···Car(↓↓)]*. Such an exciplex is suggested to play an essential role in promoting the B800 → B880 EET process, as corroborated by the recently reported cryo-EM structures of wt-LH-RC and m-LH-RC. The mechanism of Car-mediated EET will be helpful to deepen the understanding of the role of Car in bacterial photosynthesis.

Mechanistic Insights into the Halophilic Xylosidase Xylo-1 and Its Role in Xylose Production.

The Xylo-1 xylosidase, which belongs to the GH43 family, exhibits a high salt tolerance. The present study demonstrated that the catalytic activity of Xylo-1 increased by 195% in the presence of 5 M NaCl. Additionally, the half-life of Xylo-1 increased 25.9-fold in the presence of 1 M NaCl. Through comprehensive analysis including circular dichroism, fluorescence spectroscopy, and molecular dynamics simulations, we elucidated that the presence of Na+ ions increased the contact frequency between the surface acidic amino acids and the surrounding water molecules. This resulted in the stabilization of the surrounding hydration layer of Xylo-1. Additionally, Na+ ions also stabilized the substrate-binding conformation and the fluctuation of water molecules within the active site, which enhanced the catalytic activity of Xylo-1 by increasing the nucleophilic attack by the water molecules. Ultimately, the optimal reaction conditions for the production of xylose by synergistic catalysis with Xylo-1 and xylanase were determined. The results demonstrated that the conversion yield of the method was high for various sources of xylan, indicating the method could have potential industrial applications. This study explored the structure-activity relationship of catalysis in Xylo-1 under high-salt conditions, provides novel insights into the mechanism of halophilic enzymes, and serves as a reference for the industrial application of Xylo-1.

Propeptide-Mediated Allosteric Regulation of Xylanase Xyl-1: An Integrated Experimental and Computational Analysis.

Most GH11 family endo-ß-1,4-xylanases contain a propeptide region linked to the N-terminal region. The mechanistic basis of this region harboring key regulation information for enzyme function, however, remains poorly understood. We reported an investigation on the allosteric regulation mechanism of the propeptide based on biochemical characterization, molecular dynamics simulations, and evolutionary analysis. We discovered that the mutant of truncated propeptide shows a remarkably increased thermal stability (melting temperature increased by 11.5 °C) and catalytic efficiency (1.7-fold kcat/Km value of wild type). Molecular dynamics simulations reveal that long-range fluctuations in the propeptide lead to a conformational perturbation in the catalytic pocket and the thumb region. The probability of sampling the active conformation during the glycosylation step is reduced (i.e., catalytic efficiency). In-depth sequence analysis indicates that the propeptide has a strong plasticity and degeneration trend, and propeptide truncation experiments of the homologous enzyme XynB validated the feasibility of the truncation strategy. This work reveals the role of GH11 family propeptides in functional regulation and provides a straightforward and practical method to increase the robustness of GH11 family xylanases.

New insights on the photocomplex of Roseiflexus castenholzii revealed from comparisons of native and carotenoid-depleted complexes.

In wild-type phototrophic organisms, carotenoids (Crts) are primarily packed into specific pigment-protein complexes along with (Bacterio)chlorophylls and play important roles in the photosynthesis. Diphenylamine (DPA) inhibits carotenogenesis but not phototrophic growth of anoxygenic phototrophs and eliminates virtually all Crts from photocomplexes. To investigate the effect of Crts on assembly of the reaction center-light-harvesting (RC-LH) complex from the filamentous anoxygenic phototroph Roseiflexus (Rfl.) castenholzii, we generated carotenoidless (Crt-less) RC-LH complexes by growing cells in the presence of DPA. Here, we present cryo-EM structures of the Rfl. castenholzii native and Crt-less RC-LH complexes with resolutions of 2.86 Å and 2.85 Å, respectively. From the high-quality map obtained, several important but previously unresolved details in the Rfl. castenholzii RC-LH structure were determined unambiguously including the assignment and likely function of three small polypeptides, and the content and spatial arrangement of Crts with bacteriochlorophyll molecules. The overall structures of Crt-containing and Crt-less complexes are similar. However, structural comparisons showed that only five Crts remain in complexes from DPA-treated cells and that the subunit X (TMx) flanked on the N-terminal helix of the Cyt-subunit is missing. Based on these results, the function of Crts in the assembly of the Rfl. castenholzii RC-LH complex and the molecular mechanism of quinone exchange is discussed. These structural details provide a fresh look at the photosynthetic apparatus of an evolutionary ancient phototroph as well as new insights into the importance of Crts for proper assembly and functioning of the RC-LH complex.

An aminocaproic acid-grafted chitosan derivative with superior antibacterial and hemostatic properties for the prevention of secondary bleeding.

Uncontrolled bleeding is one of the leading causes of human mortality. Existing hemostatic materials or techniques cannot meet the clinical requirements for safe and effective hemostasis. The development of novel hemostatic materials has always been of great interest. Chitosan hydrochloride (CSH), a derivative of chitin, is extensively used on wounds as an antibacterial and hemostatic agent. However, the formation of intra- or intermolecular hydrogen bonds between hydroxyl and amino groups limits its water solubility and dissolution rate and affects its effectiveness in promoting coagulation. Herein, we covalently grafted aminocaproic acid (AA) to the hydroxyl and amino groups of CSH via ester and amide bonds, respectively. The solubility of CSH in water (25 °C) was 11.39 ± 0.98 % (w/v), whereas the AA-grafted CSH (CSH-AA) reached 32.34 ± 1.23 % (w/v). Moreover, the dissolution rate of CSH-AA in water was 6.46 times higher than that of CSH. Subsequent studies proved that CSH-AA is non-toxic, biodegradable, and has superior antibacterial and hemostatic properties to CSH. Additionally, anti-plasmin activity can be exerted by the dissociated AA from the CSH-AA backbone, which can help to lessen secondary bleeding.

Rhodobacter capsulatus forms a compact crescent-shaped LH1-RC photocomplex.

Rhodobacter (Rba.) capsulatus has been a favored model for studies of all aspects of bacterial photosynthesis. This purple phototroph contains PufX, a polypeptide crucial for dimerization of the light-harvesting 1-reaction center (LH1-RC) complex, but lacks protein-U, a U-shaped polypeptide in the LH1-RC of its close relative Rba. sphaeroides. Here we present a cryo-EM structure of the Rba. capsulatus LH1-RC purified by DEAE chromatography. The crescent-shaped LH1-RC exhibits a compact structure containing only 10 LH1 αß-subunits. Four αß-subunits corresponding to those adjacent to protein-U in Rba. sphaeroides were absent. PufX in Rba. capsulatus exhibits a unique conformation in its N-terminus that self-associates with amino acids in its own transmembrane domain and interacts with nearby polypeptides, preventing it from interacting with proteins in other complexes and forming dimeric structures. These features are discussed in relation to the minimal requirements for the formation of LH1-RC monomers and dimers, the spectroscopic behavior of both the LH1 and RC, and the bioenergetics of energy transfer from LH1 to the RC.

An LH1-RC photocomplex from an extremophilic phototroph provides insight into origins of two photosynthesis proteins.

Rhodopila globiformis is the most acidophilic of anaerobic purple phototrophs, growing optimally in culture at pH 5. Here we present a cryo-EM structure of the light-harvesting 1-reaction center (LH1-RC) complex from Rhodopila globiformis at 2.24 Å resolution. All purple bacterial cytochrome (Cyt, encoded by the gene pufC) subunit-associated RCs with known structures have their N-termini truncated. By contrast, the Rhodopila globiformis RC contains a full-length tetra-heme Cyt with its N-terminus embedded in the membrane forming an α-helix as the membrane anchor. Comparison of the N-terminal regions of the Cyt with PufX polypeptides widely distributed in Rhodobacter species reveals significant structural similarities, supporting a longstanding hypothesis that PufX is phylogenetically related to the N-terminus of the RC-bound Cyt subunit and that a common ancestor of phototrophic Proteobacteria contained a full-length tetra-heme Cyt subunit that evolved independently through partial deletions of its pufC gene. Eleven copies of a novel γ-like polypeptide were also identified in the bacteriochlorophyll a-containing Rhodopila globiformis LH1 complex; γ-polypeptides have previously been found only in the LH1 of bacteriochlorophyll b-containing species. These features are discussed in relation to their predicted functions of stabilizing the LH1 structure and regulating quinone transport under the warm acidic conditions.

Class A lysophosphatidic acid acyltransferase 2 from Camelina sativa promotes very long-chain fatty acids accumulation in phospholipid and triacylglycerol.

Very long-chain fatty acids (VLCFAs) are important industrial raw materials and can be produced by genetically modified oil plants. For a long time, class A lysophosphatidic acid acyltransferase (LPAT) was considered unable to promote the accumulation of VLCFA in oil crops. The bottlenecks that the transgenic high VLCFA lines have an oil content penalty and the low amount of VLCFA in phosphatidylcholine remains intractable. In the present study, a class A LPAT2 from Camelina sativa (CsaLPAT2) promoting VLCFAs accumulation in phospholipid was found. Overexpression of CsaLPAT2 alone in Arabidopsis seeds significantly increased the VLCFA content in triacylglycerol, including C20:0, C20:2, C20:3, C22:0, and C22:1. The proportion of phosphatidic acid molecules containing VLCFAs in transgenic seeds reached up to 45%, which was 2.8-fold greater than that in wild type. The proportion of phosphatidylcholine and diacylglycerol molecules containing VLCFAs also increased significantly. Seed size in CsaLPAT2 transgenic lines showed a slight increase without an oil content penalty. The total phospholipid content in the seed of the CsaLPAT2 transgenic line was significantly increased. Furthermore, the function of class A LPAT in promoting the accumulation of VLCFAs is conserved in the representative oil crops of Brassicaceae, such as C. sativa, Arabidopsis thaliana, Brassica napus, Brassica rapa, and Brassica oleracea. The findings of this study provide a promising gene resource for the production of VLCFAs.