Structure and mechanism of human cystine exporter cystinosin.

Lysosomal amino acid efflux by proton-driven transporters is essential for lysosomal homeostasis, amino acid recycling, mTOR signaling, and maintaining lysosomal pH. To unravel the mechanisms of these transporters, we focus on cystinosin, a prototypical lysosomal amino acid transporter that exports cystine to the cytosol, where its reduction to cysteine supplies this limiting amino acid for diverse fundamental processes and controlling nutrient adaptation. Cystinosin mutations cause cystinosis, a devastating lysosomal storage disease. Here, we present structures of human cystinosin in lumen-open, cytosol-open, and cystine-bound states, which uncover the cystine recognition mechanism and capture the key conformational states of the transport cycle. Our structures, along with functional studies and double electron-electron resonance spectroscopic investigations, reveal the molecular basis for the transporter's conformational transitions and protonation switch, show conformation-dependent Ragulator-Rag complex engagement, and demonstrate an unexpected activation mechanism. These findings provide molecular insights into lysosomal amino acid efflux and a potential therapeutic strategy.

Mechanism of Substrate Translocation in an Alternating Access Transporter.

Transporters shuttle molecules across cell membranes by alternating among distinct conformational states. Fundamental questions remain about how transporters transition between states and how such structural rearrangements regulate substrate translocation. Here, we capture the translocation process by crystallography and unguided molecular dynamics simulations, providing an atomic-level description of alternating access transport. Simulations of a SWEET-family transporter initiated from an outward-open, glucose-bound structure reported here spontaneously adopt occluded and inward-open conformations. Strikingly, these conformations match crystal structures, including our inward-open structure. Mutagenesis experiments further validate simulation predictions. Our results reveal that state transitions are driven by favorable interactions formed upon closure of extracellular and intracellular "gates" and by an unfavorable transmembrane helix configuration when both gates are closed. This mechanism leads to tight allosteric coupling between gates, preventing them from opening simultaneously. Interestingly, the substrate appears to take a "free ride" across the membrane without causing major structural rearrangements in the transporter.

Transport of sugars.

Soluble sugars serve five main purposes in multicellular organisms: as sources of carbon skeletons, osmolytes, signals, and transient energy storage and as transport molecules. Most sugars are derived from photosynthetic organisms, particularly plants. In multicellular organisms, some cells specialize in providing sugars to other cells (e.g., intestinal and liver cells in animals, photosynthetic cells in plants), whereas others depend completely on an external supply (e.g., brain cells, roots and seeds). This cellular exchange of sugars requires transport proteins to mediate uptake or release from cells or subcellular compartments. Thus, not surprisingly, sugar transport is critical for plants, animals, and humans. At present, three classes of eukaryotic sugar transporters have been characterized, namely the glucose transporters (GLUTs), sodium-glucose symporters (SGLTs), and SWEETs. This review presents the history and state of the art of sugar transporter research, covering genetics, biochemistry, and physiology-from their identification and characterization to their structure, function, and physiology. In humans, understanding sugar transport has therapeutic importance (e.g., addressing diabetes or limiting access of cancer cells to sugars), and in plants, these transporters are critical for crop yield and pathogen susceptibility.

Structure and thiazide inhibition mechanism of the human Na-Cl cotransporter.

The sodium-chloride cotransporter (NCC) is critical for kidney physiology1. The NCC has a major role in salt reabsorption in the distal convoluted tubule of the nephron2,3, and mutations in the NCC cause the salt-wasting disease Gitelman syndrome4. As a key player in salt handling, the NCC regulates blood pressure and is the target of thiazide diuretics, which have been widely prescribed as first-line medications to treat hypertension for more than 60 years5-7. Here we determined the structures of human NCC alone and in complex with a commonly used thiazide diuretic using cryo-electron microscopy. These structures, together with functional studies, reveal major conformational states of the NCC and an intriguing regulatory mechanism. They also illuminate how thiazide diuretics specifically interact with the NCC and inhibit its transport function. Our results provide critical insights for understanding the Na-Cl cotransport mechanism of the NCC, and they establish a framework for future drug design and for interpreting disease-related mutations.

Vertical organic electrochemical transistors for complementary circuits.

Organic electrochemical transistors (OECTs) and OECT-based circuitry offer great potential in bioelectronics, wearable electronics and artificial neuromorphic electronics because of their exceptionally low driving voltages (<1 V), low power consumption (<1 µW), high transconductances (>10 mS) and biocompatibility1-5. However, the successful realization of critical complementary logic OECTs is currently limited by temporal and/or operational instability, slow redox processes and/or switching, incompatibility with high-density monolithic integration and inferior n-type OECT performance6-8. Here we demonstrate p- and n-type vertical OECTs with balanced and ultra-high performance by blending redox-active semiconducting polymers with a redox-inactive photocurable and/or photopatternable polymer to form an ion-permeable semiconducting channel, implemented in a simple, scalable vertical architecture that has a dense, impermeable top contact. Footprint current densities exceeding 1 kA cm-2 at less than ±0.7 V, transconductances of 0.2-0.4 S, short transient times of less than 1 ms and ultra-stable switching (>50,000 cycles) are achieved in, to our knowledge, the first vertically stacked complementary vertical OECT logic circuits. This architecture opens many possibilities for fundamental studies of organic semiconductor redox chemistry and physics in nanoscopically confined spaces, without macroscopic electrolyte contact, as well as wearable and implantable device applications.

Structure and mechanism of the SGLT family of glucose transporters.

Glucose is a primary energy source in living cells. The discovery in 1960s that a sodium gradient powers the active uptake of glucose in the intestine1 heralded the concept of a secondary active transporter that can catalyse the movement of a substrate against an electrochemical gradient by harnessing energy from another coupled substrate. Subsequently, coupled Na+/glucose transport was found to be mediated by sodium-glucose cotransporters2,3 (SGLTs). SGLTs are responsible for active glucose and galactose absorption in the intestine and for glucose reabsorption in the kidney4, and are targeted by multiple drugs to treat diabetes5. Several members within the SGLT family transport key metabolites other than glucose2. Here we report cryo-electron microscopy structures of the prototypic human SGLT1 and a related monocarboxylate transporter SMCT1 from the same family. The structures, together with molecular dynamics simulations and functional studies, define the architecture of SGLTs, uncover the mechanism of substrate binding and selectivity, and shed light on water permeability of SGLT1. These results provide insights into the multifaceted functions of SGLTs.

Spin-orbit microlaser emitting in a four-dimensional Hilbert space.

A step towards the next generation of high-capacity, noise-resilient communication and computing technologies is a substantial increase in the dimensionality of information space and the synthesis of superposition states on an N-dimensional (N > 2) Hilbert space featuring exotic group symmetries. Despite the rapid development of photonic devices and systems, on-chip information technologies are mostly limited to two-level systems owing to the lack of sufficient reconfigurability to satisfy the stringent requirement for 2(N - 1) degrees of freedom, intrinsically associated with the increase of synthetic dimensionalities. Even with extensive efforts dedicated to recently emerged vector lasers and microcavities for the expansion of dimensionalities1-10, it still remains a challenge to actively tune the diversified, high-dimensional superposition states of light on demand. Here we demonstrate a hyperdimensional, spin-orbit microlaser for chip-scale flexible generation and manipulation of arbitrary four-level states. Two microcavities coupled through a non-Hermitian synthetic gauge field are designed to emit spin-orbit-coupled states of light with six degrees of freedom. The vectorial state of the emitted laser beam in free space can be mapped on a Bloch hypersphere defining an SU(4) symmetry, demonstrating dynamical generation and reconfiguration of high-dimensional superposition states with high fidelity.

Structure and mechanism of blood-brain-barrier lipid transporter MFSD2A.

MFSD2A is a sodium-dependent lysophosphatidylcholine symporter that is responsible for the uptake of docosahexaenoic acid into the brain1,2, which is crucial for the development and performance of the brain3. Mutations that affect MFSD2A cause microcephaly syndromes4,5. The ability of MFSD2A to transport lipid is also a key mechanism that underlies its function as an inhibitor of transcytosis to regulate the blood-brain barrier6,7. Thus, MFSD2A represents an attractive target for modulating the permeability of the blood-brain barrier for drug delivery. Here we report the cryo-electron microscopy structure of mouse MFSD2A. Our structure defines the architecture of this important transporter, reveals its unique extracellular domain and uncovers its substrate-binding cavity. The structure-together with our functional studies and molecular dynamics simulations-identifies a conserved sodium-binding site, reveals a potential lipid entry pathway and helps to rationalize MFSD2A mutations that underlie microcephaly syndromes. These results shed light on the critical lipid transport function of MFSD2A and provide a framework to aid in the design of specific modulators for therapeutic purposes.

Publisher Correction: Large Chinese land carbon sink estimated from atmospheric carbon dioxide data.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Large Chinese land carbon sink estimated from atmospheric carbon dioxide data.

Limiting the rise in global mean temperatures relies on reducing carbon dioxide (CO2) emissions and on the removal of CO2 by land carbon sinks. China is currently the single largest emitter of CO2, responsible for approximately 27 per cent (2.67 petagrams of carbon per year) of global fossil fuel emissions in 20171. Understanding of Chinese land biosphere fluxes has been hampered by sparse data coverage2-4, which has resulted in a wide range of a posteriori estimates of flux. Here we present recently available data on the atmospheric mole fraction of CO2, measured from six sites across China during 2009 to 2016. Using these data, we estimate a mean Chinese land biosphere sink of -1.11 ± 0.38 petagrams of carbon per year during 2010 to 2016, equivalent to about 45 per cent of our estimate of annual Chinese anthropogenic emissions over that period. Our estimate reflects a previously underestimated land carbon sink over southwest China (Yunnan, Guizhou and Guangxi provinces) throughout the year, and over northeast China (especially Heilongjiang and Jilin provinces) during summer months. These provinces have established a pattern of rapid afforestation of progressively larger regions5,6, with provincial forest areas increasing by between 0.04 million and 0.44 million hectares per year over the past 10 to 15 years. These large-scale changes reflect the expansion of fast-growing plantation forests that contribute to timber exports and the domestic production of paper7. Space-borne observations of vegetation greenness show a large increase with time over this study period, supporting the timing and increase in the land carbon sink over these afforestation regions.

Structure and mechanism of the mitochondrial Ca2+ uniporter holocomplex.

Mitochondria take up Ca2+ through the mitochondrial calcium uniporter complex to regulate energy production, cytosolic Ca2+ signalling and cell death1,2. In mammals, the uniporter complex (uniplex) contains four core components: the pore-forming MCU protein, the gatekeepers MICU1 and MICU2, and an auxiliary subunit, EMRE, essential for Ca2+ transport3-8. To prevent detrimental Ca2+ overload, the activity of MCU must be tightly regulated by MICUs, which sense changes in cytosolic Ca2+ concentrations to switch MCU on and off9,10. Here we report cryo-electron microscopic structures of the human mitochondrial calcium uniporter holocomplex in inhibited and Ca2+-activated states. These structures define the architecture of this multicomponent Ca2+-uptake machinery and reveal the gating mechanism by which MICUs control uniporter activity. Our work provides a framework for understanding regulated Ca2+ uptake in mitochondria, and could suggest ways of modulating uniporter activity to treat diseases related to mitochondrial Ca2+ overload.

Soft Fiber Electronics Based on Semiconducting Polymer.

Fibers, originating from nature and mastered by human, have woven their way throughout the entire history of human civilization. Recent developments in semiconducting polymer materials have further endowed fibers and textiles with various electronic functions, which are attractive in applications such as information interfacing, personalized medicine, and clean energy. Owing to their ability to be easily integrated into daily life, soft fiber electronics based on semiconducting polymers have gained popularity recently for wearable and implantable applications. Herein, we present a review of the previous and current progress in semiconducting polymer-based fiber electronics, particularly focusing on smart-wearable and implantable areas. First, we provide a brief overview of semiconducting polymers from the viewpoint of materials based on the basic concepts and functionality requirements of different devices. Then we analyze the existing applications and associated devices such as information interfaces, healthcare and medicine, and energy conversion and storage. The working principle and performance of semiconducting polymer-based fiber devices are summarized. Furthermore, we focus on the fabrication techniques of fiber devices. Based on the continuous fabrication of one-dimensional fiber and yarn, we introduce two- and three-dimensional fabric fabricating methods. Finally, we review challenges and relevant perspectives and potential solutions to address the related problems.

Structure and mechanism of the cation-chloride cotransporter NKCC1.

Cation-chloride cotransporters (CCCs) mediate the electroneutral transport of chloride, potassium and/or sodium across the membrane. They have critical roles in regulating cell volume, controlling ion absorption and secretion across epithelia, and maintaining intracellular chloride homeostasis. These transporters are primary targets for some of the most commonly prescribed drugs. Here we determined the cryo-electron microscopy structure of the Na-K-Cl cotransporter NKCC1, an extensively studied member of the CCC family, from Danio rerio. The structure defines the architecture of this protein family and reveals how cytosolic and transmembrane domains are strategically positioned for communication. Structural analyses, functional characterizations and computational studies reveal the ion-translocation pathway, ion-binding sites and key residues for transport activity. These results provide insights into ion selectivity, coupling and translocation, and establish a framework for understanding the physiological functions of CCCs and interpreting disease-related mutations.

GRAS gene family in rye (Secale cereale L.): genome-wide identification, phylogeny, evolutionary expansion and expression analyses.

BACKGROUND: The GRAS transcription factor family plays a crucial role in various biological processes in different plants, such as tissue development, fruit maturation, and environmental stress. However, the GRAS family in rye has not been systematically analyzed yet. RESULTS: In this study, 67 GRAS genes in S. cereale were identified and named based on the chromosomal location. The gene structures, conserved motifs, cis-acting elements, gene replications, and expression patterns were further analyzed. These 67 ScGRAS members are divided into 13 subfamilies. All members include the LHR I, VHIID, LHR II, PFYRE, and SAW domains, and some nonpolar hydrophobic amino acid residues may undergo cross-substitution in the VHIID region. Interested, tandem duplications may have a more important contribution, which distinguishes them from other monocotyledonous plants. To further investigate the evolutionary relationship of the GRAS family, we constructed six comparative genomic maps of homologous genes between rye and different representative monocotyledonous and dicotyledonous plants. The response characteristics of 19 ScGRAS members from different subfamilies to different tissues, grains at filling stages, and different abiotic stresses of rye were systematically analyzed. Paclobutrazol, a triazole-based plant growth regulator, controls plant tissue and grain development by inhibiting gibberellic acid (GA) biosynthesis through the regulation of DELLA proteins. Exogenous spraying of paclobutrazol significantly reduced the plant height but was beneficial for increasing the weight of 1000 grains of rye. Treatment with paclobutrazol, significantly reduced gibberellin levels in grain in the filling period, caused significant alteration in the expression of the DELLA subfamily gene members. Furthermore, our findings with respect to genes, ScGRAS46 and ScGRAS60, suggest that these two family members could be further used for functional characterization studies in basic research and in breeding programmes for crop improvement. CONCLUSIONS: We identified 67 ScGRAS genes in rye and further analysed the evolution and expression patterns of the encoded proteins. This study will be helpful for further analysing the functional characteristics of ScGRAS genes.

Structure and Function of Alkane Monooxygenase (AlkB).

ConspectusEvery year, perhaps as much as 800 million tons of hydrocarbons enters the environment; alkanes make up a large percentage of it. Most are transformed by organisms that utilize these molecules as sources of energy and carbon. Both aerobic and anaerobic alkane transformation chemistries exist, capitalizing on the presence of alkanes in both oxic and anoxic environments. Over the past 40 years, tremendous progress has been made in understanding the structure and mechanism of enzymes that catalyze the transformation of methane. By contrast, progress involving enzymes that transform liquid alkanes has been slower with the first structures of AlkB, the predominant aerobic alkane hydroxylase in the environment, appearing in 2023. Because of the fundamental importance of C-H bond activation chemistries, interest in understanding how biology activates and transforms alkanes is high.In this Account, we focus on steps we have taken to understand the mechanism and structure of alkane monooxygenase (AlkB), the metalloenzyme that dominates the transformation of liquid alkanes in the environment (not to be confused with another AlkB that is an α-ketogluturate-dependent enzyme involved in DNA repair). First, we briefly describe what is known about the prevalence of AlkB in the environment and its role in the carbon cycle. Then we review the key findings from our recent high-resolution cryoEM structure of AlkB and highlight important similarities and differences in the structures of members of class III diiron enzymes. Functional studies, which we summarize, from a number of single residue variants enable us to say a great deal about how the structure of AlkB facilitates its function. Next, we overview work from our laboratories using mechanistically diagnostic radical clock substrates to characterize the mechanism of AlkB and contextualize the results we have obtained on AlkB with results we have obtained on other alkane-oxidizing enzymes and explain these results in light of the enzyme's structure. Finally, we integrate recent work in our laboratories with information from prior studies of AlkB, and relevant model systems, to create a holistic picture of the enzyme. We end by pointing to critical questions that still need to be answered, questions about the electronic structure of the active site of the enzyme throughout the reaction cycle and about whether and to what extent the enzyme plays functional roles in biology beyond simply initiating the degradation of alkanes.

Improved photosynthetic performance under unilateral weak light conditions in a wide-narrow-row intercropping system is associated with altered sugar transport.

Intercropping improves resource utilization. Under wide-narrow-row maize (Zea mays) intercropping, maize plants are subjected to weak unilateral illumination and exhibit high photosynthetic performance. However, the mechanism regulating photosynthesis under unilateral weak light remains unknown. We investigated the relationship between photosynthesis and sugar metabolism in maize under unilateral weak light. Our results showed that the net photosynthetic rate (Pn) of unshaded leaves increased as the level of shade on the other side increased. On the contrary, the concentration of sucrose and starch and the number of starch granules in the unshaded leaves decreased with increased shading due to the transfer of abundant C into the grains. However, sink loss with ear removal reduced the Pn of unshaded leaves. Intense unilateral shade (40% to 20% normal light), but not mild unilateral shade (60% normal light), reduced grain yield (37.6% to 54.4%, respectively). We further found that in unshaded leaves, Agpsl, Bmy, and Mexl-like expression significantly influenced sucrose and starch metabolism, while Sweet13a and Sut1 expression was crucial for sugar export. In shaded leaves, expression of Sps1, Agpsl, and Sweet13c was crucial for sugar metabolism and export. This study confirmed that unshaded leaves transported photosynthates to the ear, leading to a decrease in sugar concentration. The improvement of photosynthetic performance was associated with altered sugar transport. We propose a narrow-row spacing of 40 cm, which provides appropriate unilateral shade and limits yield reduction.

X-ray and cryo-EM structures of the mitochondrial calcium uniporter.

Mitochondrial calcium uptake is critical for regulating ATP production, intracellular calcium signalling, and cell death. This uptake is mediated by a highly selective calcium channel called the mitochondrial calcium uniporter (MCU). Here, we determined the structures of the pore-forming MCU proteins from two fungi by X-ray crystallography and single-particle cryo-electron microscopy. The stoichiometry, overall architecture, and individual subunit structure differed markedly from those described in the recent nuclear magnetic resonance structure of Caenorhabditis elegans MCU. We observed a dimer-of-dimer architecture across species and chemical environments, which was corroborated by biochemical experiments. Structural analyses and functional characterization uncovered the roles of key residues in the pore. These results reveal a new ion channel architecture, provide insights into calcium coordination, selectivity and conduction, and establish a structural framework for understanding the mechanism of mitochondrial calcium uniporter function.

Mg2+- or Ca2+-regulated aptamer adsorption on polydopamine-coated magnetic nanoparticles for fluorescence detection of ochratoxin A.

It has been observed that polyvalent metal ions can mediate the adsorption of DNA on polydopamine (PDA) surfaces. Exploiting this, we used two divalent metal ions (Mg2+ or Ca2+) to promote the adsorption of fluorescence-labelled ochratoxin A (OTA) aptamers on PDA-coated magnetic nanoparticles (Fe3O4@PDA). Based on the different adsorption affinities of free aptamers and OTA-bound aptamers, a facile assay method was established for OTA detection. The aptamers adsorbed on Fe3O4@PDA were removed via simple magnetic separation, and the remaining aptamers in the supernatant exhibited a positive correlation with the OTA concentration. The concentrations of Mg2+ and Ca2+ were finely tuned to attain the optimal adsorption affinity and sensitivity for OTA detection. In addition, other factors, including the Fe3O4@PDA dosage, pH, mixing order, and incubation time, were studied. Finally, under optimized conditions, a detection limit (3σ/s) of 1.26 ng/mL was achieved for OTA. Real samples of spiked red wine were analysed with this aptamer-based method. This is the first report of regulating aptamer adsorption on the PDA surface with polyvalent metal ions for OTA detection. By changing the aptamers, the method can be easily extended to other target analytes.

Topological Photonic Lattice for Uniform Beam Splitting, Robust Routing, and Sensitive Far-Field Steering.

Far-field optical beam steering is a fast-growing technology for communications, spatial ranging, and detections. Nonmechanical optical phased arrays based on straight waveguides have been studied recently, where the beam emission angle to the propagation axis can be scanned by conveniently tuning the wavelength. However, the dispersion of the waveguide limits the wavelength sensitivity of beam steering and the deliberately created emitters inevitably introduce in-line backscattering on-chip. To overcome these limitations, here, we report a robust and back-reflection-free topological photonic integrated circuit, where different functionalities, such as beam splitting, routing, and far-field steering, are defined by strategic arrangements of lattices with different topological modulations simply controlled by a single lattice deformation parameter. Benefiting from the robust topological scheme, an extra band flattening is applied to achieve far-field steering with high wavelength sensitivity.

The volatile organic compounds generated from the Maillard reaction between l-ascorbic acid and l-cysteine in hot compressed water.

BACKGROUND: Hot compressed water (HCW), also known as subcritical water (SCW), refers to high-temperature compressed water in a special physical and chemical state. It is an emerging technology for natural product extraction. The volatile organic compounds (VOCs) generated from the Maillard reaction between l-ascorbic acid (ASA) and l-cysteine (Cys) have attracted significant interest in the flavor and fragrance industry. This study aimed to explore the formation mechanism of VOCs from ASA and Cys and examine the effects of reaction parameters such as temperature, time, and pH in HCW. RESULTS: The identified VOCs were predominantly thiophene derivatives, polysulfides, and pyrazine derivatives in HCW. The findings indicated that thiophene derivatives were formed under various pH conditions, with polysulfide formation favored under acidic conditions and pyrazine derivative formation preferred under weak alkaline conditions, specifically at pH 8.0. CONCLUSION: The Maillard reaction between ASA and Cys mainly produced thiophene derivatives, polysulfides, and pyrazine derivatives in HCW. The generation mechanism was significantly dependent on the surrounding pH conditions. © 2024 Society of Chemical Industry.