Crystal structure of the bacterial acetate transporter SatP reveals that it forms a hexameric channel

The ER calcium channel Csg2 integrates sphingolipid metabolism with autophagy

Sphingolipids are ubiquitous components of membranes and function as bioactive lipid signaling molecules. Here, through genetic screening and lipidomics analyses, we find that the endoplasmic reticulum (ER) calcium channel Csg2 integrates sphingolipid metabolism with autophagy by regulating ER calcium homeostasis in the yeast Saccharomyces cerevisiae. Csg2 functions as a calcium release channel and maintains calcium homeostasis in the ER, which enables normal functioning of the essential sphingolipid synthase Aur1. Under starvation conditions, deletion of Csg2 causes increases in calcium levels in the ER and then disturbs Aur1 stability, leading to accumulation of the bioactive sphingolipid phytosphingosine, which specifically and completely blocks autophagy and induces loss of starvation resistance in cells. Our findings indicate that calcium homeostasis in the ER mediated by the channel Csg2 translates sphingolipid metabolism into autophagy regulation, further supporting the role of the ER as a signaling hub for calcium homeostasis, sphingolipid metabolism and autophagy.

Transcriptomic Changes and satP Gene Function Analysis in Pasteurella multocida with Different Levels of Resistance to Enrofloxacin

Pasteurella multocida (Pm) is one of the major pathogens of bovine respiratory disease (BRD), which can develop drug resistance to many of the commonly used antibiotics. Our earlier research group found that with clinical use of enrofloxacin, Pm was more likely to develop drug resistance to enrofloxacin. In order to better understand the resistance mechanism of Pm to enrofloxacin, we isolated PmS and PmR strains with the same PFGE typing in vitro, and artificially induced PmR to obtain the highly resistant phenotype, PmHR. Then transcriptome sequencing of clinically isolated sensitive strains, resistant and highly drug-resistant strains, treated with enrofloxacin at sub-inhibitory concentrations, were performed. The satP gene, of which the expression changed significantly with the increase in drug resistance, was screened. In order to further confirm the function of this gene, we constructed a satP deletion (ΔPm) strain using suicide vector plasmid pRE112, and constructed the C-Pm strain using pBBR1-MCS, and further analyzed the function of the satP gene. Through a continuously induced resistance test, it was found that the resistance rate of ΔPm was obviously lower than that of Pm in vitro. MDK99, agar diffusion and mutation frequency experiments showed significantly lower tolerance of ΔPm than the wild-type strains. The pathogenicity of ΔPm and Pm was measured by an acute pathogenicity test in mice, and it was found that the pathogenicity of ΔPm was reduced by about 400 times. Therefore, this study found that the satP gene was related to the tolerance and pathogenicity of Pm, and may be used as a target of enrofloxacin synergistic effect.

Recent advances and challenges in the bioconversion of acetate to value-added chemicals

Acetate is a major byproduct of the bioconversion of the greenhouse gas carbon dioxide, pretreatment of lignocellulose biomass, and microbial fermentation. The utilization and valorization of acetate have been emphasized in transforming waste to clean energy and value-added platform chemicals, contributing to the development of a closed carbon loop toward a low-carbon circular bio-economy. Acetate has been used to produce several platform chemicals, including succinate, 3-hydroxypropionate, and itaconic acid, highlighting the potential of acetate to synthesize many biochemicals and biofuels. On the other hand, the yields and titers have not reached the theoretical maximum. Recently, recombinant strain development and pathway regulation have been suggested to overcome this limitation. This review provides insights into the important constraints limiting the yields and titers of the biochemical and metabolic pathways of bacteria capable of metabolizing acetate for acetate bioconversion. The current developments in recombinant strain engineering are also discussed.

Ion selectivity and gating behavior of the CorA-type channel Bpss1228

Magnesium is an essential element to sustain all forms of life. Total intracellular magnesium content is determined by the balance of magnesium influx and efflux. CorA is a divalent selective channel in the metal ion transport superfamily and is the major Mg²⁺ uptake pathway in prokaryotes and eukaryotic mitochondria. Previous studies have demonstrated that CorA showed distinct magnesium bound closed conformation and Mg²⁺-free states. In addition, CorA is regulated by cytoplasmic magnesium ions and its gating mechanism has been investigated by electron paramagnetic resonance technique and molecular dynamic simulations. Here, we report a study of the putative CorA-type channel Bpss1228 from Burkholderia pseudomallei, which has been shown to be significantly associated with pseudomallei infection. We expressed and purified the Bpss1228 in full-length. Subsequently, electrophysiological experiments further investigated the electrical characteristics of Bpss1228 and revealed that it was a strictly cation-selective channel. We also proved that Bpss1228 not only possessed magnesium-mediated regulatory property a remarkable ability to be modulated by magnesium ions. Finally, we observed the three-step gating behavior of Bpss1228 on planar lipid bilayer, and further proposed a synergistic gating mechanism by which CorA family channels control intracellular magnesium homeostasis.

The Dicarboxylate Transporters from the AceTr Family and Dct-02 Oppositely Affect Succinic Acid Production in S. cerevisiae

Membrane transporters are important targets in metabolic engineering to establish and improve the production of chemicals such as succinic acid from renewable resources by microbial cell factories. We recently provided a Saccharomyces cerevisiae strain able to strongly overproduce succinic acid from glycerol and CO₂ in which the Dct-02 transporter from Aspergillus niger, assumed to be an anion channel, was used to export succinic acid from the cells. In a different study, we reported a new group of succinic acid transporters from the AceTr family, which were also described as anion channels. Here, we expressed these transporters in a succinic acid overproducing strain and compared their impact on extracellular succinic acid accumulation with that of the Dct-02 transporter. The results show that the tested transporters of the AceTr family hinder succinic acid accumulation in the extracellular medium at low pH, which is in strong contrast to Dct-02. Data suggests that the AceTr transporters prefer monovalent succinate, whereas Dct-02 prefers divalent succinate anions. In addition, the results provided deeper insights into the characteristics of Dct-02, showing its ability to act as a succinic acid importer (thus being bidirectional) and verifying its capability of exporting malate.

Comparative Genomics of Members of the Genus Defluviicoccus With Insights Into Their Ecophysiological Importance

Members of the genus Defluviicoccus occur often at high abundances in activated sludge wastewater treatment plants designed to remove phosphorus, where biomass is subjected to alternating anaerobic feed/aerobic famine conditions, believed to favor the proliferation of organisms like Ca. Accumulibacter and other phosphate-accumulating organisms (PAO), and Defluviicoccus. All have a capacity to assimilate readily metabolizable substrates and store them intracellularly during the anaerobic feed stage so that under the subsequent famine aerobic stage, these can be used to synthesize polyphosphate reserves by the PAO and glycogen by Defluviicoccus. Consequently, Defluviicoccus is described as a glycogen-accumulating organism or GAO. Because they share a similar anaerobic phenotype, it has been proposed that at high Defluviicoccus abundance, the PAO are out-competed for assimilable metabolites anaerobically, and hence aerobic P removal capacity is reduced. Several Defluviicoccus whole genome sequences have been published (Ca. Defluviicoccus tetraformis, Defluviicoccus GAO-HK, and Ca. Defluviicoccus seviourii). The available genomic data of these suggest marked metabolic differences between them, some of which have ecophysiological implications. Here, we describe the whole genome sequence of the type strain Defluviicoccus vanus^T, the only cultured member of this genus, and a detailed comparative re-examination of all extant Defluviicoccus genomes. Each, with one exception, which appears not to be a member of this genus, contains the genes expected of GAO members, in possessing multiple copies of those for glycogen biosynthesis and catabolism, and anaerobic polyhydroxyalkanoate (PHA) synthesis. Both 16S rRNA and genome sequence data suggest that the current recognition of four clades is insufficient to embrace their phylogenetic biodiversity, but do not support the view that they should be re-classified into families other than their existing location in the Rhodospirillaceae. As expected, considerable variations were seen in the presence and numbers of genes encoding properties associated with key substrate assimilation and metabolic pathways. Two genomes also carried the pit gene for synthesis of the low-affinity phosphate transport protein, pit, considered by many to distinguish all PAO from GAO. The data re-emphasize the risks associated with extrapolating the data generated from a single Defluviicoccus population to embrace all members of that genus.

The substrate import mechanism of the human serotonin transporter

The serotonin transporter (SERT) initiates the reuptake of extracellular serotonin in the synapse to terminate neurotransmission. The cryogenic electron microscopy structures of SERT bound to ibogaine and the physiological substrate serotonin resolved in different states have provided a glimpse of the functional conformations at atomistic resolution. However, the conformational dynamics and structural transitions to intermediate states are not fully understood. Furthermore, the molecular basis of how serotonin is recognized and transported remains unclear. In this study, we performed unbiased microsecond-long simulations of the human SERT to investigate the structural dynamics to various intermediate states and elucidated the complete substrate import pathway. Using Markov state models, we characterized a sequential order of conformational-driven ion-coupled substrate binding and transport events and calculated the free energy barriers of conformation transitions associated with the import mechanism. We find that the transition from the occluded to inward-facing state is the rate-limiting step for substrate import and that the substrate decreases the free energy barriers to achieve the inward-facing state. Our study provides insights on the molecular basis of dynamics-driven ion-substrate recognition and transport of SERT that can serve as a model for other closely related neurotransmitter transporters.

Biological nanopores for sensing applications

Biological nanopores are proteins with transmembrane pore that can be embedded in lipid bilayer. With the development of single-channel current measurement technologies, biological nanopores have been reconstituted into planar lipid bilayer and used for single-molecule sensing of various analytes and events such as single-molecule DNA sensing and sequencing. To improve the sensitivity for specific analytes, various engineered nanopore proteins and strategies are deployed. Here, we introduce the origin and principle of nanopore sensing technology as well as the structure and associated properties of frequently used protein nanopores. Furthermore, sensing strategies for different applications are reviewed, with focus on the alteration of buffer condition, protein engineering, and deployment of accessory proteins and adapter-assisted sensing. Finally, outlooks for de novo design of nanopore and nanopore beyond sensing are discussed.

Uncovering Novel Plasma Membrane Carboxylate Transporters in the Yeast Cyberlindnera jadinii

The yeast Cyberlindnera jadinii has great potential in the biotechnology industry due to its ability to produce a variety of compounds of interest, including carboxylic acids. In this work, we identified genes encoding carboxylate transporters from this yeast species. The functional characterization of sixteen plasma membrane carboxylate transporters belonging to the AceTr, SHS, TDT, MCT, SSS, and DASS families was performed by heterologous expression in Saccharomyces cerevisiae. The newly identified C. jadinii transporters present specificity for mono-, di-, and tricarboxylates. The transporters CjAto5, CjJen6, CjSlc5, and CjSlc13-1 display the broadest substrate specificity; CjAto2 accepts mono- and dicarboxylates; and CjAto1,3,4, CjJen1-5, CjSlc16, and CjSlc13-2 are specific for monocarboxylic acids. A detailed characterization of these transporters, including phylogenetic reconstruction, 3D structure prediction, and molecular docking analysis is presented here. The properties presented by these transporters make them interesting targets to be explored as organic acid exporters in microbial cell factories.

ATP Synthase K+- and H+-Fluxes Drive ATP Synthesis and Enable Mitochondrial K+-"Uniporter" Function: I. Characterization of Ion Fluxes

ATP synthase (F₁F_o) synthesizes daily our body's weight in ATP, whose production-rate can be transiently increased several-fold to meet changes in energy utilization. Using purified mammalian F₁F_o-reconstituted proteoliposomes and isolated mitochondria, we show F₁F_o can utilize both ΔΨ_m-driven H⁺- and K⁺-transport to synthesize ATP under physiological pH = 7.2 and K⁺ = 140 mEq/L conditions. Purely K⁺-driven ATP synthesis from single F₁F_o molecules measured by bioluminescence photon detection could be directly demonstrated along with simultaneous measurements of unitary K⁺ currents by voltage clamp, both blocked by specific F_o inhibitors. In the presence of K⁺, compared to osmotically-matched conditions in which this cation is absent, isolated mitochondria display 3.5-fold higher rates of ATP synthesis, at the expense of 2.6-fold higher rates of oxygen consumption, these fluxes being driven by a 2.7:1 K⁺: H⁺ stoichiometry. The excellent agreement between the functional data obtained from purified F₁F_o single molecule experiments and ATP synthase studied in the intact mitochondrion under unaltered OxPhos coupling by K⁺ presence, is entirely consistent with K⁺ transport through the ATP synthase driving the observed increase in ATP synthesis. Thus, both K⁺ (harnessing ΔΨ_m) and H⁺ (harnessing its chemical potential energy, Δμ_H) drive ATP generation during normal physiology.

New insights into the acetate uptake transporter (AceTr) family: Unveiling amino acid residues critical for specificity and activity

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Substrate specificity of Ato1 was engineered by altering its pore size.

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The L219A and F98A substitutions enable succinic acid transport activity of Ato1.

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Ato1 E144A substitution causes dominant negative organic acid hypersensitivity.

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Organic acid hypersensitivity is caused by the hyperactive ATO1 transporter alleles.

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First report of a fully functional bacterial transporter (SatP) in yeast.

Aiming at improving the transport of biotechnologically relevant carboxylic acids in engineered microbial cell factories, the focus of this work was to study plasma membrane transporters belonging to the Acetate Uptake Transporter (AceTr) family. Ato1 and SatP, members of this family from Saccharomyces cerevisiae and Escherichia coli, respectively, are the main acetate transporters in these species. The analysis of conserved amino acid residues within AceTr family members combined with the study of Ato1 3D model based on SatP, was the rationale for selection of site-directed mutagenesis targets. The library of Ato1-GFP mutant alleles was functionally analysed in the S. cerevisiae IMX1000 strain which shows residual growth in all carboxylic acids tested. A gain of function phenotype was found for mutations in the residues F98 and L219 located at the central constrictive site of the pore, enabling cells to grow on lactic and on succinic acid. This phenotype was associated with an increased transport activity for these substrates. A dominant negative acetic acid hypersensitivity was induced in S. cerevisiae cells expressing the E144A mutant, which was associated with an increased acetic acid uptake. By utilizing computer-assisted 3D-modelling tools we highlight structural features that explain the acquired traits found in the analysed Ato1 mutants. Additionally, we achieved the proper expression of the Escherichia coli SatP, a homologue of Ato1, in S. cerevisiae. To our knowledge, this constitutes the first report of a fully functional bacterial plasma membrane transporter protein in yeast cells.

Solid-State NMR Studies of the Succinate-Acetate Permease from Citrobacter Koseri in Liposomes and Native Nanodiscs

The succinate-acetate permease (SatP) is an anion channel with six transmembrane domains. It forms different oligomers, especially hexamers in the detergent as well as in the membrane. Solid-state NMR studies of SatP were carried out successfully on SatP complexes by reconstructing the protein into liposomes or retaining the protein in the native membrane of E. coli., where it was expressed. The comparison of ¹³C-¹³C 2D correlation spectra between the two samples showed great similarity, opening the possibility to further study the acetate transport mechanism of SatP in its native membrane environment. Solid-state NMR studies also revealed small chemical shift differences of SatP in the two different membrane systems, indicating the importance of the lipid environment in determining the membrane protein structures and dynamics. Combining different 2D SSNMR spectra, chemical shift assignments were made on some sites, consistent with the helical structures in the transmembrane domains. In the end, we pointed out the limitation in the sensitivity for membrane proteins with such a size, and also indicated possible ways to overcome it.

Niche partitioning in the Rimicaris exoculata holobiont: the case of the first symbiotic Zetaproteobacteria

BACKGROUND

Free-living and symbiotic chemosynthetic microbial communities support primary production and higher trophic levels in deep-sea hydrothermal vents. The shrimp Rimicaris exoculata, which dominates animal communities along the Mid-Atlantic Ridge, houses a complex bacterial community in its enlarged cephalothorax. The dominant bacteria present are from the taxonomic groups Campylobacteria, Desulfobulbia (formerly Deltaproteobacteria), Alphaproteobacteria, Gammaproteobacteria, and some recently discovered iron oxyhydroxide-coated Zetaproteobacteria. This epibiotic consortium uses iron, sulfide, methane, and hydrogen as energy sources. Here, we generated shotgun metagenomes from Rimicaris exoculata cephalothoracic epibiotic communities to reconstruct and investigate symbiotic genomes. We collected specimens from three geochemically contrasted vent fields, TAG, Rainbow, and Snake Pit, to unravel the specificity, variability, and adaptation of Rimicaris-microbe associations.

RESULTS

Our data enabled us to reconstruct 49 metagenome-assembled genomes (MAGs) from the TAG and Rainbow vent fields, including 16 with more than 90% completion and less than 5% contamination based on single copy core genes. These MAGs belonged to the dominant Campylobacteria, Desulfobulbia, Thiotrichaceae, and some novel candidate phyla radiation (CPR) lineages. In addition, most importantly, two MAGs in our collection were affiliated to Zetaproteobacteria and had no close relatives (average nucleotide identity ANI < 77% with the closest relative Ghiorsea bivora isolated from TAG, and 88% with each other), suggesting potential novel species. Genes for Calvin-Benson Bassham (CBB) carbon fixation, iron, and sulfur oxidation, as well as nitrate reduction, occurred in both MAGs. However, genes for hydrogen oxidation and multicopper oxidases occurred in one MAG only, suggesting shared and specific potential functions for these two novel Zetaproteobacteria symbiotic lineages. Overall, we observed highly similar symbionts co-existing in a single shrimp at both the basaltic TAG and ultramafic Rainbow vent sites. Nevertheless, further examination of the seeming functional redundancy among these epibionts revealed important differences.

CONCLUSION

These data highlight microniche partitioning in the Rimicaris holobiont and support recent studies showing that functional diversity enables multiple symbiont strains to coexist in animals colonizing hydrothermal vents. Video Abstract.

Acetate as a potential feedstock for the production of value-added chemicals: Metabolism and applications

Acetate is regarded as a promising carbon feedstock in biological production owing to its possible derivation from C₁ gases such as CO, CO₂ and methane. To best use of acetate, comprehensive understanding of acetate metabolisms from genes and enzymes to pathways and regulations is needed. This review aims to provide an overview on the potential of acetate as carbon feedstock for industrial biotechnology. Biochemical, microbial and biotechnological aspects of acetate metabolism are described. Especially, the current state-of-the art in the production of value-added chemicals from acetate is summarized. Challenges and future perspectives are also provided.

State-of-the-art web services for de novo protein structure prediction

Residue coevolution estimations coupled to machine learning methods are revolutionizing the ability of protein structure prediction approaches to model proteins that lack clear homologous templates in the Protein Data Bank (PDB). This has been patent in the last round of the Critical Assessment of Structure Prediction (CASP), which presented several very good models for the hardest targets. Unfortunately, literature reporting on these advances often lacks digests tailored to lay end users; moreover, some of the top-ranking predictors do not provide webservers that can be used by nonexperts. How can then end users benefit from these advances and correctly interpret the predicted models? Here we review the web resources that biologists can use today to take advantage of these state-of-the-art methods in their research, including not only the best de novo modeling servers but also datasets of models precomputed by experts for structurally uncharacterized protein families. We highlight their features, advantages and pitfalls for predicting structures of proteins without clear templates. We present a broad number of applications that span from driving forward biochemical investigations that lack experimental structures to actually assisting experimental structure determination in X-ray diffraction, cryo-EM and other forms of integrative modeling. We also discuss issues that must be considered by users yet still require further developments, such as global and residue-wise model quality estimates and sources of residue coevolution other than monomeric tertiary structure.

Carboxylic Acid Transporters in Candida Pathogenesis

Opportunistic pathogens such as Candida species can use carboxylic acids, like acetate and lactate, to survive and successfully thrive in different environmental niches. These nonfermentable substrates are frequently the major carbon sources present in certain human body sites, and their efficient uptake by regulated plasma membrane transporters plays a critical role in such nutrient-limited conditions. Here, we cover the physiology and regulation of these proteins and their potential role in Candida virulence.

Opportunistic pathogens such as Candida species can use carboxylic acids, like acetate and lactate, to survive and successfully thrive in different environmental niches. These nonfermentable substrates are frequently the major carbon sources present in certain human body sites, and their efficient uptake by regulated plasma membrane transporters plays a critical role in such nutrient-limited conditions. Here, we cover the physiology and regulation of these proteins and their potential role in Candida virulence. This review also presents an evolutionary analysis of orthologues of the Saccharomyces cerevisiae Jen1 lactate and Ady2 acetate transporters, including a phylogenetic analysis of 101 putative carboxylate transporters in twelve medically relevant Candida species. These proteins are assigned to distinct clades according to their amino acid sequence homology and represent the major carboxylic acid uptake systems in yeast. While Jen transporters belong to the sialate:H⁺ symporter (SHS) family, the Ady2 homologue members are assigned to the acetate uptake transporter (AceTr) family. Here, we reclassify the later members as ATO (acetate transporter ortholog). The new nomenclature will facilitate the study of these transporters, as well as the analysis of their relevance for Candida pathogenesis.

Failure to Maintain Acetate Homeostasis by Acetate-Activating Enzymes Impacts Plant Development

The metabolic intermediate acetyl-CoA links anabolic and catabolic processes and coordinates metabolism with cellular signaling by influencing protein acetylation. In this study we demonstrate that in Arabidopsis (Arabidopsis thaliana), two distinctly localized acetate-activating enzymes, ACETYL-COA SYNTHETASE (ACS) in plastids and ACETATE NON-UTILIZING1 (ACN1) in peroxisomes, function redundantly to prevent the accumulation of excess acetate. In contrast to the near wild-type morphological and metabolic phenotypes of acs or acn1 mutants, the acs acn1 double mutant is delayed in growth and sterile, which is associated with hyperaccumulation of cellular acetate and decreased accumulation of acetyl-CoA-derived intermediates of central metabolism. Using multiple mutant stocks and stable isotope-assisted metabolic analyses, we demonstrate the twin metabolic origins of acetate from the oxidation of ethanol and the nonoxidative decarboxylation of pyruvate, with acetaldehyde being the common intermediate precursor of acetate. Conversion from pyruvate to acetate is activated under hypoxic conditions, and ACS recovers carbon that would otherwise be lost from the plant as ethanol. Plastid-localized ACS metabolizes cellular acetate and contributes to the de novo biosynthesis of fatty acids and Leu; peroxisome-localized ACN1 enables the incorporation of acetate into organic acids and amino acids. Thus, the activation of acetate in distinct subcellular compartments provides plants with the metabolic flexibility to maintain physiological levels of acetate and a metabolic mechanism for the recovery of carbon that would otherwise be lost as ethanol, for example following hypoxia.

T2* weighted Deconvolution of NMR Spectra: Application to 2D Homonuclear MAS Solid-State NMR of Membrane Proteins

2D homonuclear NMR spectroscopy is an essential technique to characterize small and large molecules, such as organic compounds, metabolites, and biomacromolecules at atomic resolution. However, for complex samples 2D homonuclear spectra display poor resolution, making spectral assignment very cumbersome. Here, we propose a new method that exploits the differential T2* relaxation times of individual resonances and resolves the 2D NMR peaks into pseudo-3D spectra, where time is the 3rd dimension. T2* weIghted DEconvolution or TIDE analyzes individual free induction decays (FIDs) and dissects them into sub-FIDs that are transformed into pseudo-3D spectra combining Fourier transformation and covariance NMR. TIDE achieves higher resolution and sensitivity for NMR spectra than classical covariance NMR reducing offset-dependent artifacts. We demonstrate the performance of TIDE for magic angle spinning (MAS) [13C,13C]-DARR NMR spectra of single- and multi-span membrane proteins embedded in lipid bilayers. Since TIDE is applicable to all type of homonuclear correlation experiments for liquid and solid samples, we anticipate that it will be a general method for processing NMR data of biomacromolecules, complex mixtures of metabolites as well as material samples.

Characterization of the GPR1/FUN34/YaaH protein family in the green microalga Chlamydomonas suggests their role as intracellular membrane acetate channels

The unicellular green microalga Chlamydomonas reinhardtii is a powerful photosynthetic model organism which is capable of heterotrophic growth on acetate as a sole carbon source. This capacity has enabled its use for investigations of perturbations in photosynthetic machinery as mutants can be recovered heterotrophically. Fixation of acetate into cellular carbon metabolism occurs first by its conversion into acetyl-CoA by a respective synthase and the generation of succinate by the glyoxylate cycle. These metabolic steps have been recently determined to largely occur in the peroxisomes of this alga; however, little is known about the trafficking and import of acetate or its subcellular compartmentalization. Recently, the genes of five proteins belonging to the GPR1/FUN34/YaaH (GFY) superfamily were observed to exhibit increased expression in C. reinhardtii upon acetate addition, however, no further characterization has been reported. Here, we provide several lines of evidence to implicate Cr GFY1-5 as channels which share structural homology with bacterial succinate-acetate channels and specifically localize to microbodies, which are surprisingly distinct from the glyoxylate cycle-containing peroxisomes. We demonstrate structural models, gene expression profiling, and in vivo fluorescence localization of all five isoforms in the algal cell to further support this role.

Hybridization of TEDOR and NCX MAS solid-state NMR experiments for simultaneous acquisition of heteronuclear correlation spectra and distance measurements

Magic angle spinning (MAS) solid-state NMR (ssNMR) spectroscopy is a major technique for the characterization of the structural dynamics of biopolymers at atomic resolution. However, the intrinsic low sensitivity of this technique poses significant limitations to its routine application in structural biology. Here we achieve substantial savings in experimental time using a new subclass of Polarization Optimized Experiments (POEs) that concatenate TEDOR and SPECIFIC-CP transfers into a single pulse sequence. Specifically, we designed new 2D and 3D experiments (2D TEDOR-NCX, 3D TEDOR-NCOCX, and 3D TEDOR-NCACX) to obtain distance measurements and heteronuclear chemical shift correlations for resonance assignments using only one experiment. We successfully tested these experiments on N-Acetyl-Val-Leu dipeptide, microcrystalline U-13C,15N ubiquitin, and single- and multi-span membrane proteins reconstituted in lipid membranes. These pulse sequences can be implemented on any ssNMR spectrometer equipped with standard solid-state hardware using only one receiver. Since these new POEs speed up data acquisition considerably, we anticipate their broad application to fibrillar, microcrystalline, and membrane-bound proteins.