Comprendre le rôle de RecN dans la voie de réparation CDB chez Deinococcus radiodurans

Deinococcus radiodurans est une bactérie à gram-positive connue pour son extrême résistance à une grande variété d'agents endommageant l'ADN. Parmi ces derniers, les rayonnements ionisants et la dessiccation sont les plus nocifs pour la cellule, car ils introduisent des cassures dans le génome. Les cassures double brin (CDB) sont particulièrement dangereuses et doivent être réparées de façon très efficace, afin d'éviter l'apparition de mutations pouvant mener à la mort de la cellule ou de l'organisme. La recombinaison homologue (RH) est le mécanisme le plus efficace pour la réparation des CDBs. D. radiodurans est capable de restaurer entièrement son génome en à peine 3 heures, et elle accomplit la totalité du processus par la voie RecFOR. Afin d'être réparées, les CDBs doivent d'abord être reconnu. Cette étape importante, qui a lieu peu de temps après l'apparition du dommage dans la cellule, implique la protéine RecN. RecN est recrutée dès les premières étapes de la réparation de l'ADN et des études in vivo ont démontré qu'elle avait tendance à se localiser dans des foyers discrets. Des études in vitro suggèrent également que RecN favorise l'assemblage de fragments d'ADN, une fonction décrite précédemment pour les protéines SMC (telle que cohesin), qui sont structurellement similaires à RecN. De nombreuses études structurales ont été effectuées sur la protéine de type SMC, Rad50, alors qu'à présent aucune information structurale n'est disponible pour RecN. Le travail présenté ici a porté sur la caractérisation structurale de RecN et de ses domaines. Nous avons obtenu les structures cristallines de trois constructions (se chevauchant partiellement) de RecN et une étude de diffusions des rayons X aux petits angles a été effectuée sur les domaines séparés de RecN et sur la protéine entière. Les données obtenues en solution ont complété notre étude cristallographique et nous ont permis de construire un modèle atomique de la protéine entière. Des mutations ont été conçues et les protéines mutées ont été produites et utilisées pour la caractérisation de l'activité d'hydrolyse de l'ATP caractéristique de cette famille de protéines. Des études biochimiques approfondies ont été effectuées sur les différentes constructions et mutants de RecN afin de déterminer le rôle de chacun des ses domaines. Nos résultat nous ont permis de proposer un modèle qui explique comment RecN reconnaît les CDB, maintient les deux extrémités de l'ADN, et prépare l'ADN pour la réparation par les protéines RecFOR.Deinococcus radiodurans is a Gram-positive bacterium known for its extreme resistance to a broad variety of DNA damaging agents. Among these, Ionizing Radiations and desiccation are the most harmful for the cell, since they introduce breaks in the genome. Double Strand Breaks (DSB) are particularly hazardous for the cell and they need to be repaired very efficiently, in order to avoid mutations leading to altered, if not lethal, phenotypes. Homologous Recombination (HR) is the most efficient mechanism by which DSBs are repaired. D. radiodurans is able to completely restore its genome in only 3 hours, and it accomplishes the entire process through the RecFOR pathway. In order to be repaired, DSBs first need to be recognized. The protein believed to be responsible for this important step that takes place soon after the damage occurs in the cell, is RecN. RecN is recruited at the early stages of DNA repair and in vivo studies have demonstrated its propensity to localize to discrete foci. In vitro studies also suggest that RecN possesses a DNA end-joining activity previously observed for SMC proteins (such as cohesin), which are structurally related to RecN. Several structural studies have been carried out on the SMC-like protein, Rad50, but so far no structural information is available for RecN. The work presented here focused on the structural characterization of RecN and its constitutive domains. We obtained crystal structures of three partially overlapping constructs of RecN and Small Angle X-ray Scattering was performed on the individual domains and the full-length protein. The study of RecN in solution complemented our crystallographic study and enabled us to build a reliable, atomic model of the full-length protein. Mutations were designed and the mutant RecN proteins were produced in order to characterize the ATP hydrolysis activity of RecN, which is a conserved feature of this family of proteins. Extensive biochemical studies were carried out on wild-type and mutants of both the full-length protein and the single domains, in order to determine the role and function of each of the domains. Our results led us to propose a model for how RecN might recognize DSBs, tether two broken DNA ends and prepare the DNA for subsequent repair by the RecFOR machinery.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Hip and Groin Pain in the Professional Athlete

AbstractHip and groin pain is a common condition in professional athletes and may result from an acute injury or from chronic, repetitive trauma. It is responsible for significant morbidity, which leads to time away from training and competition, and may result in a career-ending injury. The anatomic and biomechanical causes for hip and groin injuries are among the most complex and controversial in the musculoskeletal system. This makes clinical differentiation and subsequent management difficult because of the considerable overlap of symptoms and signs. This review article will evaluate several pathologic conditions of the hip and groin in athletes, divided into acute (secondary to single event) and chronic (secondary to altered biomechanical load or repetitive microtrauma) injuries, with an emphasis on imaging in the diagnosis of these injuries. Appropriate use of imaging along with clinical findings can allow accurate diagnosis and subsequent appropriate management of these patients to ultimately allow return to athletic activity

An 'open' structure of the RecOR complex supports ssDNA binding within the core of the complex

International audienceEfficient DNA repair is critical for cell survival and the maintenance of genome integrity. The homolo-gous recombination pathway is responsible for the repair of DNA double-strand breaks within cells. Initiation of this pathway in bacteria can be carried out by either the RecBCD or the RecFOR proteins. An important regulatory player within the RecFOR pathway is the RecOR complex that facilitates RecA loading onto DNA. Here we report new data regarding the assembly of Deinococcus radiodurans RecOR and its interaction with DNA, providing novel mechanistic insight into the mode of action of RecOR in homologous recombination. We present a higher resolution crystal structure of RecOR in an 'open' conformation in which the tetrameric RecR ring flanked by two RecO molecules is ac-cessible for DNA binding. We show using small-angle neutron scattering and mutagenesis studies that DNA binding does indeed occur within the RecR ring. Binding of single-stranded DNA occurs without any major conformational changes of the RecOR complex while structural rearrange-ments are observed on double-stranded DNA binding. Finally, our molecular dynamics simula-tions, supported by our biochemical data, provide a detailed picture of the DNA binding motif of RecOR and reveal that single-stranded DNA is sand-wiched between the two facing oligonucleotide binding domains of RecO within the RecR ring

Water sorption and hydration in spray-dried milk protein powders: Selected physicochemical properties

peer-reviewedLow and high protein dairy powders are prone to caking and sticking and can also be highly insoluble; with powder storage conditions an important factor responsible for such issues. The aim of this study focused on the bulk and surface properties of anhydrous and humidified spray-dried milk protein concentrate (MPC) powders (protein content ~40, 50, 60, 70 or 80%, w/w). Water sorption isotherms, polarized light and scanning electron micrographs showed crystallized lactose in low protein powders at high water activities. High protein systems demonstrated increased bulk diffusion coefficients compared to low protein systems. Glass transition temperatures, α-relaxation temperatures and structural strength significantly decreased with water uptake. CLSM measurements showed that humidified systems have slower real time water diffusion compared to anhydrous systems. Overall, the rate of water diffusion was higher for low protein powders but high protein powders absorbed higher levels of water under high humidity conditions

Contactless, probeless and non-titrimetric determination of acid-base reactions using Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS)

pH determination is a routine measurement in scientific laboratories worldwide. Most major advances in pH measurement were made in the 19th and early 20th century. pH measurements are critical for the determination of acid base reactions. This study demonstrates how an acid-base reaction can be monitored without the use of a pH probe, indicator and titres of reagent. The stoichiometric reaction between carbonate and HCl acid yields specific quantities of CO2, which causes reproducible changes to the compressibility of the solvent. This in turn slows down the speed of sound in solution which is induced by a magnetic follower gently tapping the inner wall of the vessel. As a consequence the frequencies of the acoustic resonances in the vessel are reduced. This approach is called Broadband Acoustic Resonance Dissolution Spectroscopy (BARDS) which harnesses this phenomenon for many applications. The acid-carbonate experiments have also been validated using H2SO4 acid and using both potassium and sodium counterions for the carbonate. This method can be used to interrogate strong acid-base reactions in a rapid and non-invasive manner using carbonate as the base. The data demonstrates the first example of a reactant also acting as an indicator. The applicability of the method to weak acids has yet to be determined. A novel conclusion from the study is that a person with a well-trained ear is capable of determining the concentration and pH of a strong acid just by listening. This brings pH measurement into the realm of human perception

Colouring cryo-cooled crystals: online microspectrophotometry

A portable and readily aligned online microspectrophotometer that can be easily installed on macromolecular crystallography beamlines is described. It allows measurement of the spectral characteristics of macromolecular crystals prior, during, and after the X-ray diffraction experiment

How coenzyme B12 radicals are generated: the crystal structure of methylmalonyl-coenzyme A mutase at 2 å resolution

AbstractBackground: The enzyme methylmalonyl-coenzyme A (CoA) mutase, an αβ heterodimer of 150 kDa, is a member of a class of enzymes that uses coenzyme B12 (adenosylcobalamin) as a cofactor. The enzyme induces the formation of an adenosyl radical from the cofactor. This radical then initiates a free-radical rearrangement of its substrate, succinyl-CoA, to methylmalonyl-CoA.Results Reported here is the crystal structure at 2 å resolution of methylmalonyl-CoA mutase from Propionibacterium shermanii in complex with coenzyme B12 and with the partial substrate desulpho-CoA (lacking the succinyl group and the sulphur atom of the substrate). The coenzyme is bound by a domain which shares a similar fold to those of flavodoxin and the B12-binding domain of methylcobalamin-dependent methionine synthase. The cobalt atom is coordinated, via a long bond, to a histidine from the protein. The partial substrate is bound along the axis of a (β/α)8 TIM barrel domain.Conclusion The histidine–cobalt distance is very long (2.5 å compared with 1.95–2.2 å in free cobalamins), suggesting that the enzyme positions the histidine in order to weaken the metal–carbon bond of the cofactor and favour the formation of the initial radical species. The active site is deeply buried, and the only access to it is through a narrow tunnel along the axis of the TIM barrel domain

A Nutrient Formulation Affects Developmental Myelination in Term Infants: A Randomized Clinical Trial

Background and Objectives: Observational studies suggest differences between breast-fed and formula-fed infants in developmental myelination, a key brain process for learning. The study aims to investigate the efficacy of a blend of docosahexaenoic acid (DHA), arachidonic acid (ARA), iron, vitamin B12, folic acid, and sphingomyelin (SM) from a uniquely processed whey protein concentrate enriched in alpha-lactalbumin and phospholipids compared with a control formulation on myelination, cognitive, and behavioral development in the first 6 months of life. Methods: These are 6-month results from an ongoing two-center, randomized controlled trial with a 12-month intervention period (completed for all participants). In this study, full term, neurotypical infants of both sexes (N = 81) were randomized into investigational (N = 42) or control groups (N = 39). In addition, non-randomized breast-fed children (N = 108) serve as a natural reference group. Main outcomes are myelination (MRI), cognitive (Bayley Scales of Infant and Toddler Development, 3rd edition [Bayley-III]), social-emotional development (Ages and Stages Questionnaires: Social-Emotional, 2nd edition [ASQ:SE-2]), sleep (Brief Infant Sleep Questionnaire [BISQ]), and safety (growth and adverse events [AEs]). Results: The full analyses set comprises N = 66 infants. Significant differences in myelin structure, volume, and rate of myelination were observed in favor of the investigational myelin blend at 3 and 6 months of life. Effects were demonstrated for whole brain myelin and for cerebellar, parietal, occipital, and temporal regions, known to be functionally involved in sensory, motor, and language skills. No statistically significant differences were found for early behavior and cognition scores. Conclusions: This is the first study demonstrating the efficacy of a myelin nutrient blend in well-nourished, term infants on developmental myelination, which may be foundational for later cognitive and learning outcomes.publishedVersio

A decade of user operation on the macromolecular crystallography MAD beamline ID14-4 at the ESRF

The improvement of the X-ray beam quality achieved on ID14-4 by the installation of new X-ray optical elements is described

The temperature-dependent conformational ensemble of SARS-CoV-2 main protease (Mpro)

The COVID-19 pandemic, instigated by the SARS-CoV-2 coronavirus, continues to plague the globe. The SARS-CoV-2 main protease, or Mpro, is a promising target for development of novel antiviral therapeutics. Previous X-ray crystal structures of Mpro were obtained at cryogenic temperature or room temperature only. Here we report a series of high-resolution crystal structures of unliganded Mpro across multiple temperatures from cryogenic to physiological, and another at high humidity. We interrogate these datasets with parsimonious multiconformer models, multi-copy ensemble models, and isomorphous difference density maps. Our analysis reveals a temperature-dependent conformational landscape for Mpro, including mobile solvent interleaved between the catalytic dyad, mercurial conformational heterogeneity in a key substrate-binding loop, and a far-reaching intramolecular network bridging the active site and dimer interface. Our results may inspire new strategies for antiviral drug development to counter-punch COVID-19 and combat future coronavirus pandemics