A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle.

Biological carbon fixation is a key step in the global carbon cycle that regulates the atmosphere's composition while producing the food we eat and the fuels we burn. Approximately one-third of global carbon fixation occurs in an overlooked algal organelle called the pyrenoid. The pyrenoid contains the CO2-fixing enzyme Rubisco and enhances carbon fixation by supplying Rubisco with a high concentration of CO2 Since the discovery of the pyrenoid more that 130 y ago, the molecular structure and biogenesis of this ecologically fundamental organelle have remained enigmatic. Here we use the model green alga Chlamydomonas reinhardtii to discover that a low-complexity repeat protein, Essential Pyrenoid Component 1 (EPYC1), links Rubisco to form the pyrenoid. We find that EPYC1 is of comparable abundance to Rubisco and colocalizes with Rubisco throughout the pyrenoid. We show that EPYC1 is essential for normal pyrenoid size, number, morphology, Rubisco content, and efficient carbon fixation at low CO2 We explain the central role of EPYC1 in pyrenoid biogenesis by the finding that EPYC1 binds Rubisco to form the pyrenoid matrix. We propose two models in which EPYC1's four repeats could produce the observed lattice arrangement of Rubisco in the Chlamydomonas pyrenoid. Our results suggest a surprisingly simple molecular mechanism for how Rubisco can be packaged to form the pyrenoid matrix, potentially explaining how Rubisco packaging into a pyrenoid could have evolved across a broad range of photosynthetic eukaryotes through convergent evolution. In addition, our findings represent a key step toward engineering a pyrenoid into crops to enhance their carbon fixation efficiency

Geometrical, Flexural and Vibroacoustical Characterization of Saxophone Reeds

The sound production by the saxophone, a single-reed wind instrument, relies mainly on the control of the vibration of a plate by the player’s lower lip and the air blown into the instrument. This vibrating plate is securely attached to the mouthpiece and is known as a reed. In this study, we have investigated eight different reeds, including both (natural) cane reeds and reeds made of synthetic materials, compared their design, material and vibroacoustic properties. The long-term aim of this study is to facilitate the fabrication of reeds aiming to aide musicians in customizing their reeds aligning with their specific needs

Analyse microtomographique et vibroacoustique d'anches synthétiques pour saxophone

Profitant des innovations en ingénierie des matériaux depuis plusieurs décennies, des anches synthétiques pour saxophone et clarinette sont apparues sur le marché dans le but de répondre aux attentes des fabricants et des musiciens à la fois en termes de prédictibilité, de reproductibilité et de durabilité. Nous proposons ici une étude comparative de différentes anches disponibles actuellement dans le commerce. Dans cette étude exploratoire, nous nous concentrons sur une étude de paramètres objectifs, sans inclure l'instrumentiste. Le premier volet porte sur l'analyse d’images des anches obtenues par micro-tomographique à rayons X. Elle permet un relevé tridimensionnel des géométries et l'examen de la structure interne des matériaux. La variété des profils d'épaisseurs est mise en rapport avec l'architecture des matériaux (naturelle pour les fibres de roseau, tissée et/ou renforcée pour les composites, et fragmentée pour les anches à base de poudre). Dans un second temps, les anches sont montées sur un bec de saxophone - sans lèvre artificielle - et soumises à des essais vibro-acoustiques par sollicitation acoustique via le bec et mesure des champs de déplacement transverse par vibrométrie laser à effet Doppler. On s'intéresse tout d'abord aux fréquences de résonance et aux facteurs de qualité associés. La variabilité liée aux incertitudes de montage d'une même anche sur le bec est comparée à la variabilité entre différentes anches d'une même série, puis entre les différentes conceptions d'anches synthétiques, confirmant le caractère discriminant des essais vibro-acoustiques

Dimensionnement, fabrication et caractérisation d'anches de saxophone en composite à fibre de lin Design, manufacture and characterisation of flax fibre composite saxophone reeds

Single-reed wind instruments, such as the saxophone, have a vibrating plate attached to the mouthpiece. The musician creates the vibrations by blowing into the space between the reed and the mouthpiece, which produces the sound. This vibrating plate is called the reed. Traditionally, saxophone reeds are made from natural cane (Arundo Donax), but to overcome problems of variability and durability, synthetic reeds of various types have been developed. The project is part of an ambitious partnership between the Materials and Structures team, the LMA Sound team and the start-up SYOS. The aim is to develop saxophone reeds made from flax fibre composites that are more durable and of consistent quality (i.e. more reproducible than reed reeds), while at the same time creating a catalogue of reeds associated with the musical sensations of the saxophonist.Dans les instruments à vent à anche simple tels que le saxophone, une plaque vibrante est fixée à l'embouchure. Le musicien génère les vibrations en soufflant dans l'espace entre l'anche et le bec, ce qui crée le son. Cette plaque vibrante est appelée anche. Traditionnellement, les anches de saxophone sont fabriquées en canne naturelle (Arundo Donax L), mais afin de surmonter les problèmes de variabilité et de durabilité, des anches synthétiques de différents types ont été développées. Le projet se place dans le cadre d'un partenariat ambitieux entre l'équipe matériaux et structures, l'équipe son du LMA et de la start-up SYOS. Il se propose de développer des anches de saxophone en matériaux composites à fibre de lin plus durables et de qualité constante (i.e. plus reproductibles que les anches en roseau) tout en créant un catalogue d'anches associées aux ressentis musicaux du saxophoniste

A repeat protein links Rubisco to form the eukaryotic carbon-concentrating organelle.

Biological carbon fixation is a key step in the global carbon cycle that regulates the atmosphere's composition while producing the food we eat and the fuels we burn. Approximately one-third of global carbon fixation occurs in an overlooked algal organelle called the pyrenoid. The pyrenoid contains the CO2-fixing enzyme Rubisco and enhances carbon fixation by supplying Rubisco with a high concentration of CO2 Since the discovery of the pyrenoid more that 130 y ago, the molecular structure and biogenesis of this ecologically fundamental organelle have remained enigmatic. Here we use the model green alga Chlamydomonas reinhardtii to discover that a low-complexity repeat protein, Essential Pyrenoid Component 1 (EPYC1), links Rubisco to form the pyrenoid. We find that EPYC1 is of comparable abundance to Rubisco and colocalizes with Rubisco throughout the pyrenoid. We show that EPYC1 is essential for normal pyrenoid size, number, morphology, Rubisco content, and efficient carbon fixation at low CO2 We explain the central role of EPYC1 in pyrenoid biogenesis by the finding that EPYC1 binds Rubisco to form the pyrenoid matrix. We propose two models in which EPYC1's four repeats could produce the observed lattice arrangement of Rubisco in the Chlamydomonas pyrenoid. Our results suggest a surprisingly simple molecular mechanism for how Rubisco can be packaged to form the pyrenoid matrix, potentially explaining how Rubisco packaging into a pyrenoid could have evolved across a broad range of photosynthetic eukaryotes through convergent evolution. In addition, our findings represent a key step toward engineering a pyrenoid into crops to enhance their carbon fixation efficiency

Initial Steps in Methanobactin Biosynthesis: Substrate Binding by the Mixed-Valent Diiron Enzyme MbnBC

The MbnBC enzyme complex converts cysteine residues in a peptide substrate, MbnA, to oxazolone/thioamide groups during the biosynthesis of copper chelator methanobactin (Mbn). MbnBC belongs to the mixed-valent diiron oxygenase (MVDO) family, of which members use an Fe(II)Fe(III) cofactor to react with dioxygen for substrate modification. Several crystal structures of the inactive Fe(III)Fe(III) form of MbnBC alone and in complex with MbnA have been reported, but a mechanistic understanding requires determination of the oxidation states of the crystallographically observed Fe ions in the catalytically active Fe(II)Fe(III) state, along with the site of MbnA binding. Here, we have used electron nuclear double resonance (ENDOR) spectroscopy to determine such structural and electronic properties of the active site, in particular, the mode of substrate binding to the MV state, information not accessible by X-ray crystallography alone. The oxidation states of the two Fe ions were determined by 15N ENDOR analysis. The presence and locations of both bridging and terminal exogenous solvent ligands were determined using 1H and 2H ENDOR. In addition, 2H ENDOR using an isotopically labeled MbnA substrate indicates that MbnA binds to the Fe(III) ion of the cluster via the sulfur atom of its N-terminal modifiable cysteine residue, with displacement of a coordinated solvent ligand as shown by complementary 1H ENDOR. These results, which underscore the utility of ENDOR in studying MVDOs, provide a molecular picture of the initial steps in Mbn biosynthesis

The Short- and Long-Run Determinants of Less-Educated Immigrant Flows into U.S. States

We use a gravity model of migration and alternative estimation strategies to analyse how income differentials affect the flow of immigrants into U.S. states using annual data from the American Community Survey. We add to existing literature by decomposing income differentials into short- and long-term components and by focusing on newly arrived less-educated immigrants between 2000-2009. Our sample is unique in that the vast majority of our observations take zero values. Models that include observations with zero flow values find that recent male immigrants respond to differences in (short-term) GDP fluctuations between origin countries and U.S. states, and perhaps to (long-term) trend GDP differences as well. More specifically, GDP fluctuations pull less-educated male immigrants into certain U.S. states, whereas GDP trends push less-educated male immigrants out of their countries of origin. Effects for less-educated women are less robust, as GDP coefficients tend to be much smaller than for men