9 research outputs found
An objective reduction technique of proteomic mass spectra based on multi-scale fuzzy thresholding
A proteomic approach offers a powerful and complementary tool to genomics. It allows to index and characterize
proteins, and, for example, to compare their levels of expression between healthy and pathological states. Proteomic
analyses are mainly based on the separation of proteins by two-dimensional gel electrophoresis and their subsequent
identification by comparing the data from Mass Spectrometry (SM) analyses to the theoretical ones contained in
databases.
In mass spectrometry, the detector noise, the electronic and chemical noise, sometimes the small amount of peptides
that has to be treated and finally the spectrum reduction noise (due to bad filtering and/or thresholding), can induce
Parasitic Mass Peaks (PMP) and/or hide some Useful Mass Peaks (UMP) of low intensities. The immediate consequence
is that the presence of the PMP and the absence of the UMP will be detrimental to the protein identification quality. In
this article, we propose an original algorithm eliminating the PMP, detecting and amplifying those which are useful. The
preprocessing principle uses a multi-scale analysis technique coupled to a fuzzy thresholding (multi-scale fuzzy
thresholding), a local amplification of the UMP, and finally an adaptive Base Line Correction.
The associated frequencies with the PMP are distributed on all the spectrum pass bandwidth. This leads us to a dyadic
tree structure subband decomposition. The algorithm principle consists of dividing the frequential pass bandwidth of
each masses spectrum into two subbands, a Low and High Frequency (LF,HF) subband, then each subband is in turn
divided into two subbands etc. The HF subbands are then thresholded according to the minimization criterion of the
Shannon fuzzy entropy, and then amplified locally; the base line is calculated in an adaptive way and subtracted from
reconstructed spectrum. To evaluate the quality of this algorithm, we present a comparison of the results obtained by
our algorithm, and those obtained by the DataExplorer software. The latter is a reduction software provided within the
MALDI-TOF spectrometer software package.La protéomique offre une approche puissante et complémentaire à la génomique. Elle permet de répertorier et
caractĂ©riser les protĂ©ines, de comparer leur niveau dâexpression entre un Ă©tat physiologique sain et malade
par exemple. Lâanalyse protĂ©omique se fait essentiellement par lâutilisation de la technique dâĂ©lectrophorĂšse
bidimensionnelle couplĂ©e Ă la technique dâanalyse par SpectromĂ©trie de Masse (SM). La premiĂšre, aidĂ©e par
lâimagerie protĂ©omique, conduit Ă la localisation des protĂ©ines candidates Ă une analyse par SM. La
comparaison des spectres de masses obtenus Ă des bases de donnĂ©es protĂ©iques, conduit Ă lâidentification
des protĂ©ines dâintĂ©rĂȘt en terme de peptides. Le problĂšme qui se pose souvent est que les spectres sont
bruités et pauvres en masses. En effet, le bruit du détecteur, le bruit électronique et chimique, la présence de
peu de matériel protéique et enfin le bruit de la réduction des spectres (mauvais filtrage et/ou seuillage), tous
ces bruits peuvent induire des Pics de Masses Parasites (PMP) et/ou supprimer des Pics de Masses Utiles
(PMU) de faible intensitĂ©. La consĂ©quence immĂ©diate est que la prĂ©sence des PMP et lâabsence des PMU
seront utilisĂ©es au dĂ©pens de la qualitĂ© dâidentification de la protĂ©ine.
Dans cet article, nous proposons un algorithme original éliminant les PMP, détectant et amplifiant ceux utiles.
Le principe du pré-traitement utilise une Analyse Multirésolution (AM) couplée à un seuillage basé sur la
logique floue (seuillage flou multi-Ă©chelle), une amplification locale des PMU, et enfin une correction
adaptative de la Ligne de Base (LB). Les fréquences associées aux PMP sont réparties sur toute la bande
passante du spectre, ce qui nous conduit à une AM dite en arbre. Le principe consiste à découper la bande
passante frĂ©quentielle de chaque spectre de masses en deux sous-bandes, une Basse FrĂ©quence (BF), lâautre
Haute Fréquence (HF), ensuite chaque sous-bande est à son tour découpée en deux sous-bandes etc. Les
sous-bandes HF sont seuillĂ©es selon le critĂšre de minimisation de lâentropie floue de Shannon et amplifiĂ©es
localement, la ligne de base est calculée automatiquement et soustraite du spectre reconstruit. Pour évaluer
la qualité de cet algorithme, nous présentons une comparaison des résultats obtenus par notre algorithme, et
ceux fournis par le spectromĂštre MALDI-TOF (Matrix Assisted Laser Desorption/Ionisation-Time Of Flight), qui
utilise le logiciel « DataExplorer » comme logiciel de réduction
Implication de HMGB1 dans la différentiation des trophoblastes
Le placenta est l'organe essentiel au succÚs de la grossesse et la différenciation
des trophoblastes est fondamentale pour son bon fonctionnement. La présence
dâune inflammation non contrĂŽlĂ©e, habituellement induite par des mĂ©diateurs inflammatoires
endogÚnes, est associée à plusieurs complications de la grossesse. High
Mobility Group Box 1 (HMGB1), une protéine nucléaire qui peut avoir des actions inflammatoires
lorsque secrétée dans le milieu extracellulaire, est un des médiateurs
inflammatoires endogÚnes augmentés lors des grossesses pathologiques. Cependant,
la maniĂšre dont HMGB1 agit Ă lâinterface materno-foetale est encore inconnue.
Ce travail de maĂźtrise a comme objectifs dâĂ©valuer la concentration, la localisation
subcellulaire et la sécrétion de HMGB1 lors de la différentiation des trophoblastes et
dâĂ©tudier sa distribution dans le placenta de grossesses compliquĂ©es par une prĂ©eclampsie
(PE).
Dans ces travaux, nous avons démontré une augmentation de la concentration
nucléaire de HMGB1 lors de la différenciation spontanée des trophoblastes. De
plus, lâutilisation dâun inhibiteur dâhistones dĂ©acĂ©tylases (c.-Ă -d. NaB) mĂšne Ă une accumulation
de HMGB1 dans le cytoplasme et favorise la différenciation, tandis que
lâutilisation dâun inhibiteur de lâexport nuclĂ©aire (c.-Ă -d. leptomycine) mĂšne Ă une diminution
de la différenciation. En ce qui concerne les grossesses compliquées par la
PE, il y a une redistribution de HMGB1 avec une accumulation cytoplasmique. En
conclusion, ces travaux dĂ©montrent lâassociation entre la modulation de HMGB1 et la
différentiation des trophoblastes, bien que le lien causal reste à déterminer.The placenta plays a crucial role during pregnancy and trophoblast differentiation
is fundamental to its proper functioning. The absence of inflammation is also essential
for the success of gestation, the presence of uncontrolled inflammation is associated
with several pregnancy complications, such as preeclampsia (PE) and preterm
delivery. High Mobility Group Box 1 (HMGB1), a nuclear protein that acts as a
pro-inflammatory mediator when secreted into the extracellular media, is one of the
endogenous inflammatory mediators increased during pathological pregnancies. However,
the actions of HMGB1 at the materno-fetal interface are still unknown. The aim
of this work was to evaluate the concentration, subcellular localization and secretion
of HMGB1 during trophoblast differentiation and to evaluate the distribution of
HMGB1 in the placenta from pregnancies complicated with PE.
In my studies I have shown an increase of HMGB1âs nuclear concentration during
the spontaneous differentiation of trophoblasts. Moreover, the use of a histone
deacetylase inhibitor (i.e. NaB) leads to an accumulation of HMGB1 in the cytoplasm
and promotes differentiation, while the use of a nuclear export inhibitor (i.e. leptomycin)
leads to a decrease in differentiation. Concerning pregnancies complicated with
PE, there is a redistribution of HMGB1 with cytoplasmic accumulation.
In conclusion, this work demonstrates the association between the modulation
of HMGB1 localisation with trophoblasts differentiation, although the causal link remains
to be determined
The regulation and induction of clathrin-mediated endocytosis through a protein aqueous-aqueous phase separation mechanism
La morphologie des cellules et leurs interactions avec lâenvironnement dĂ©coulent de divers procĂ©dĂ©s mĂ©caniques qui contribuent Ă la richesse et Ă la diversitĂ© de la vie qui nous entoure. Ă titre dâexemple, les cellules mammifĂšres se conforment Ă diffĂ©rentes gĂ©omĂ©tries en fonction de lâarchitecture de leur cytosquelette tandis que les bactĂ©ries et les levures adoptent une forme circulaire par turgescence.
Je prĂ©sente, dans cette thĂšse, la dĂ©couverte dâun mĂ©canisme de morphogĂ©nĂšse supplĂ©mentaire, soit la dĂ©formation de surface cellulaire via lâassemblage de protĂ©ines par dĂ©mixtion de phases aqueuses non miscibles et lâadhĂ©sion entre les matĂ©riaux biologiques. Jâexpose de façon spĂ©cifique comment ce mĂ©canisme rĂ©gule le recrutement et le mouvement dynamique des protĂ©ines qui induisent lâinvagination de la membrane plasmique lors de lâendocytose clathrine-dĂ©pendante (CME).
Le phĂ©nomĂšne de dĂ©mixtion des protĂ©ines dans le cytoplasme est analogue Ă la sĂ©paration de phase de lâhuile en solution aqueuse. Il constitue un mĂ©canisme cellulaire important et conservĂ©, oĂč les protĂ©ines sâagglomĂšrent grĂące aux interactions intermolĂ©culaires qui supplantent la tendance du systĂšme Ă former un mĂ©lange homogĂšne.
Plusieurs exemples de compartiments cellulaires dĂ©pourvus de membrane se forment par dĂ©mixtion de phase, tels que le nuclĂ©ole et les granules de traitement de lâARN [1-6]. Ces organes ou compartiments dĂ©nommĂ©s NMO, du terme anglais « non-membranous organelles », occupent des fonctions de stockage, de traitement et de modification chimique des molĂ©cules dans la cellule. Jâexplore ici les questions suivantes : est-ce que les NMO occupent dâautres fonctions Ă caractĂšre morphologique ? Quels signaux cellulaires rĂ©gulent la dĂ©mixtion de phase des protĂ©ines dans la formation des NMO ?
FondĂ©e sur la physique mĂ©canique du contact entre les matĂ©riaux, jâĂ©mets lâhypothĂšse que des compartiments cellulaires nanoscopiques, formĂ©s par dĂ©mixtion de phase, gĂ©nĂšrent des forces mĂ©caniques par adhĂ©sion interfaciale. Le travail mĂ©canique ainsi obtenu dĂ©forme le milieu cellulaire et les surfaces membranaires adjacents au NMO nouvellement crĂ©Ă©.
Le but de mon doctorat est de comprendre comment les cellules orchestrent, dans le temps et lâespace, la formation des NMO associĂ©s au CME et comment ceux-ci gĂ©nĂšrent des forces mĂ©caniques.
Mes travaux se concentrent sur les mĂ©canismes de dĂ©mixtion de phase et dâadhĂ©sion de contact dans le processus dâendocytose chez la levure Saccharomyces cerevisiae. Pour enquĂȘter sur le rĂŽle des modifications post-traductionnelles dans ces mĂ©canismes, nous avons premiĂšrement analysĂ© la cinĂ©tique de phosphorylation des protĂ©ines en conditions de stress. Mes rĂ©sultats dĂ©montrent que le recrutement et la fonction de certaines protĂ©ines impliquĂ©es dans le CME se rĂ©gulent via des mĂ©canismes de phosphorylation.
Outre les processus de contrĂŽle post-traductionnel, nous avons Ă©lucidĂ© le rĂŽle des domaines de faible complexitĂ© dans lâassemblage de plusieurs protĂ©ines associĂ©es avec le CME. De concert avec les modifications de phosphorylation, des domaines dâinteraction protĂ©ine-protĂ©ine de type PrD (du terme « prion-like domains ») modulent directement le recrutement des protĂ©ines au sein des NMO associĂ©s au CME. La nature intrinsĂšquement dĂ©sordonnĂ©e de ces PrD favorise un mĂ©canisme dâassemblage des protĂ©ines par dĂ©mixtion de phase tel que postulĂ©. Finalement, mes travaux confirment que la formation de ces NMO spĂ©cifiques gĂ©nĂšre des forces mĂ©caniques qui dĂ©forment la membrane plasmique et assurent le processus de CME.
Dâun point de vue fondamental, mes recherches permettent de mieux comprendre lâĂ©volution dâune stratĂ©gie cellulaire pour assembler des compartiments cellulaires sans membrane et pour fixer les dimensions biologiques associĂ©es au CME. De maniĂšre plus appliquĂ©e, cette Ă©tude a le potentiel de gĂ©nĂ©rer des retombĂ©es importantes dans la comprĂ©hension et le traitement de maladies neurodĂ©gĂ©nĂ©ratives souvent associĂ©es Ă une sĂ©paration de phase aberrante et Ă la formation dâagrĂ©gats protĂ©iques liĂ©s Ă la pathologie.Evolution has resulted in distinct mechanical processes that determine the shapes of living cells and their interactions with each other and with the environment. These molecular mechanisms have contributed to the wide variety of life we observe today. For example, mammalian cells rely on a complex cytoskeleton to adapt specific shapes whereas bacteria, yeast and plants use a combination of turgor pressure and cell walls to have their characteristic bloated form.
In this dissertation, I describe my discovery of an unforeseen additional mechanism of morphogenesis: protein aqueous-aqueous phase separation and adhesive contact between biomaterials as a simple and efficient ways for cells to organize internal matter and accomplish work to shape internal structures and surfaces. I specifically describe how a fundamental process of phospholipid membrane and membrane-embedded protein recycling, clathrin-mediated endocytosis (CME), is driven by this mechanism.
Analogous to water and oil emulsions, proteins, and biopolymers in general, can phase separate from single to a binary aqueous phase. For proteins that de-mix from the bulk environment, the intermolecular interactions (or cohesive energy) that favors protein condensation only needs to overcome the low mixing entropy of the system and represents a conserved and energy efficient cellular strategy [2, 3, 7, 8].
So far, various examples of phase separated cellular compartments, termed non-membranous organelles (NMOs), have been discovered. These include the nucleoli, germ line P granules and P bodies, to name a few [1-6]. NMOs are involved in many conserved biological processes and can function as storage, bioreactor or signaling bodies. Cells use phase separation as a scheme to organize internal matter, but do NMOs occupy other complex functions, such as morphogenesis? What specific signals trigger protein phase separation?
Based on mechanical contact theory, I proposed that hundreds of nanometer- to micron-scale phase separated bodies can deform the cellular environment, both cytoplasm and membranes, through interfacial adhesion.
I studied how mechanical contact between a phase-separated protein fluid droplet and CME nucleation sites on membranes drive endocytosis in the model organism budding yeast, Saccharomyces cerevisiae. Specifically, this dissertation describes first, my investigations of post-translational modifications (phosphorylation) of several CME-mediating proteins and the implications of these modifications in regulating CME. I then describe how my efforts to understand what was distinct about the proteins that are phosphorylated led me to propose their phase separation into droplets capable of driving invagination and vesicle formation from plasma membrane.
I used fluorescence microscopy, mass spectrometry and micro rheology techniques to respectively determine the spatiotemporal dynamics, phosphorylation modifications and material properties of coalesced CME-mediating proteins. I further investigated how phase separation of these proteins might generate mechanical force.
I demonstrate that changes in the phosphorylation of some endocytic proteins regulates their recruitment to CME nucleation sites. We achieved reliable predictions of functional phosphosites by combining information on the conservation of the post-translational modifications with analysis of the proportion of a protein that is dynamically phosphorylated with time.
The same dynamically phosphorylated proteins were enriched for low amino acid compositional complexity âprion-like domainsâ, which we demonstrated were essential to these proteins undergoing aqueous-aqueous phase separation on CME nucleation sites. I then demonstrate how phase separated droplet can produce mechanical work to invaginate membranes and drive CME to completion.
In summary, I have discovered a fundamental molecular mechanism by which phase separated biopolymers and membranes could apply work to shape each other. This mechanism determines the natural selection of spatial scale and material properties of CME. Finally, I discuss broader implications of this dissertation to mechanistic understandings of the origins of neurodegenerative diseases, which likely involve pathological forms of protein phase separation and/or aggregation
Ătude des propriĂ©tĂ©s gĂ©lifiantes et viscosifiantes de systĂšmes mixtes isolat de protĂ©ines de lactosĂ©rum-polysaccharides en conditions associatives
Les interactions entre protĂ©ines et polysaccharides dĂ©pendent des conditions environnementales et de leurs propriĂ©tĂ©s intrinsĂšques. La cosolubilitĂ©, la complexation et lâincompatibilitĂ© en sont le rĂ©sultat. La complexation et lâincompatibilitĂ© ont dĂ©montrĂ© une amĂ©lioration des propriĂ©tĂ©s fonctionnelles de systĂšmes mixtes comparativement aux biopolymĂšres pris individuellement. LâincompatibilitĂ© Ă©tant souvent la rĂšgle, cette recherche a pour but dâapprofondir les connaissances sur les propriĂ©tĂ©s fonctionnelles des systĂšmes mixtes protĂ©ines-polysaccharides en conditions de compatibilitĂ© ou dâinteractions associatives et de caractĂ©riser les nouvelles fonctionnalitĂ©s qui en dĂ©coulent. Un premier systĂšme isolat de protĂ©ines de lactosĂ©rum-xanthane a Ă©tĂ© Ă©tudiĂ© pour ses aptitudes Ă la gĂ©lification en conditions de compatibilitĂ© induites suite Ă une variation de pH et du ratio protĂ©ines-polysaccharides. Suivant lâapplication dâun traitement thermique, la solution est passĂ©e de compatible Ă incompatible. Les gels dĂ©montraient une augmentation du module Ă©lastique (Gâ) due Ă lâincompatibilitĂ© telle quâobservĂ©e par microscopie confocale Ă balayage laser. Lâajout de NaCl a augmentĂ© cette incompatibilitĂ© et lâa rendue excessive au-delĂ dâune concentration critique entraĂźnant une chute du Gâ. La compatibilitĂ© a ensuite Ă©tĂ© Ă©tudiĂ©e sur un systĂšme isolat de protĂ©ines de lactosĂ©rum-pectine. Suite Ă une variation de pH, de la concentration en biopolymĂšres et du ratio protĂ©ines-polysaccharides, des conditions de compatibilitĂ© ont Ă©tĂ© confirmĂ©es par les mesures dâabsorbance et du nombre de charges. Cette compatibilitĂ© a menĂ© Ă une diminution de la viscositĂ© en solution diluĂ©e due Ă la formation de complexes solubles alors quâen solution concentrĂ©e, la complexation lâa plutĂŽt augmentĂ©e. Un systĂšme modĂšle de yogourt ferme a finalement Ă©tĂ© Ă©tudiĂ© suite Ă lâincorporation de isolat de protĂ©ines de lactosĂ©rum et de pectine prĂ©alablement complexĂ©s et stabilisĂ©s. Les concentrations en protĂ©ines et en solides totaux ont Ă©tĂ© maintenues constantes. Les mĂ©langes laitiers ont Ă©tĂ© acidifiĂ©s au glucono-delta-lactone. Les rĂ©sultats dĂ©montrent que lâincorporation de complexes Ă diffĂ©rentes concentrations entrave la formation dâun rĂ©seau protĂ©ique homogĂšne provoquant une diminution de la fermetĂ© du gel et une augmentation de la synĂ©rĂšse. Les observations microscopiques appuient ces rĂ©sultats. Les solutions mixtes permettent de dĂ©velopper de nouvelles propriĂ©tĂ©s fonctionnelles. Cependant, une meilleure connaissance de ces mĂ©langes est nĂ©cessaire pour en arriver Ă des propriĂ©tĂ©s fonctionnelles variĂ©es et prĂ©cises dans les formulations alimentaires.Protein polysaccharide interactions depend on both environmental conditions and intrinsic properties. Results are co-solubility, complexation and incompatibility. Complexation and incompatibility have demonstrated improvement of functional properties of mixed systems compared to those of the individual components. Incompatibility being the rule, the aim of this study is to widen knowledge on functional properties of mixed protein-polysaccharide systems in presence of compatibility or associative interactions and to characterise the new emerging functional properties. A first mixed system of whey protein isolate-xanthan has been studied for its gelling abilities following pH and protein-polysaccharide ratio variations. Following application of a thermal treatment, the solution passed from compatible to incompatible. Gelation was demonstrated by an increase in elastic modulus (Gâ) due to incompatibility as observed by confocal laser scanning microscopy. Addition of NaCl increased this incompatibility and made it excessive at a certain critical concentration leading to loss in Gâ. Compatibility has then been studied on a whey protein isolate-pectin system. Varying pH, biopolymer total concentration and protein-polysaccharide ratio allowed soluble complex formation which was confirmed with the measurement of absorbance and the number of charge. This compatibility led to a decrease in viscosity in diluted solution due to soluble complex formation while in concentrated solution, complexation rather increased it. A model system of firm yogurt was finally studied following incorporation of whey protein isolate and pectin first complexed and stabilised. Protein and total solid concentrations were kept constant. Milky solutions were acidified with glucono-delta-lactone. Results demonstrate that incorporation of complexes at different concentrations hampers the formation of a homogenous protein network provoking a decrease in gel stiffness and an increase in syneresis. Microscopic observations supported these conclusions. Mixed solutions prepared by carefully condunting complex formation allow the design of new functional properties. However, a better knowledge of these mixes is necessary in order to achieve varied and precise functional properties in food formulation
Compréhension du rÎle structural d'exopolysaccharides de bactéries lactiques dans des systÚmes laitiers fermentés enrichis en amidon modifié
Au Canada, lâutilisation dâamidon modifiĂ© dans le yogourt est usuel afin dâĂ©viter des dĂ©fauts de qualitĂ© comme la synĂ©rĂšse. MalgrĂ© cet ajout, les dĂ©fauts demeurent. Les exopolysaccharides (EPS) produits naturellement par certaines bactĂ©ries lactiques suscitent un intĂ©rĂȘt technologique dus Ă leur capacitĂ© de rĂ©tention dâeau et Ă moduler la viscositĂ©. La structure des EPS et leurs interactions avec les protĂ©ines seraient responsables de ces effets plutĂŽt que de la concentration produite. JusquâĂ prĂ©sent, aucune Ă©tude nâa Ă©tĂ© rĂ©alisĂ©e sur lâutilisation conjointe dâamidon modifiĂ© et dâEPS dans les yogourts. Le but de ce travail Ă©tait dâĂ©tudier le rĂŽle structural des EPS produits in situ par certaines bactĂ©ries lactiques sur les propriĂ©tĂ©s rhĂ©ologiques/physiques (formation de gel, fermetĂ©, viscositĂ©, synĂ©rĂšse) et la microstructure de systĂšmes laitiers avec amidon modifiĂ©. Quatre ferments constituĂ©s chacun dâune souche de Streptococcus thermophilus et dâune souche de Lactobacillus delbrueckii ssp. bulgaricus, produisant des EPS aux caractĂ©ristiques structurales connues, ont Ă©tĂ© utilisĂ©s: HC15/210R (contrĂŽle), HC15/291 (EPS neutre, rigide, peu ramifiĂ©), HC15/702074 (EPS neutre, flexible, hautement ramifiĂ©), 2104/210R (EPS chargĂ©, rigide, linĂ©aire). Le pH final de 4.6 a Ă©tĂ© atteint pour tous les ferments aprĂšs 180-210 minutes Ă 42 C. Le processus de formation de gel nâa pas Ă©tĂ© influencĂ© par la prĂ©sence dâEPS. La comparaison de plusieurs EPS aux structures connues a permis dâĂ©tablir que lâEPS chargĂ© du ferment 2104/210R amĂ©liorait la fermetĂ© en plus de contribuer Ă la viscositĂ©. LâEPS neutre, rigide et peu ramifiĂ© du ferment HC15/291 amĂ©liorait significativement la viscositĂ© et la rĂ©tention du sĂ©rum comparativement Ă lâEPS neutre, hautement ramifiĂ© et flexible du ferment HC15/702074. MalgrĂ© que le lissage ait diminuĂ© significativement les propriĂ©tĂ©s rhĂ©ologiques/physiques des systĂšmes laitiers, la fonctionnalitĂ© des EPS est maintenue. Lâajout dâamidon modifiĂ© a amĂ©liorĂ© les propriĂ©tĂ©s rhĂ©ologiques/physiques des systĂšmes laitiers brassĂ©s tandis que peu dâeffets ont Ă©tĂ© observĂ©s pour les systĂšmes laitiers fermes. Finalement, ce travail a dĂ©montrĂ© quâil est possible dâamĂ©liorer les propriĂ©tĂ©s rhĂ©ologiques/physiques de systĂšmes laitiers par lâutilisation conjointe dâEPS aux caractĂ©ristiques structurales spĂ©cifiques et dâamidon modifiĂ©.In Canada, modified starch addition in yoghurt is frequent in order to limit technological defects such as syneresis. Despite the addition of modified starch, technological defects still occur. Exopolysaccharides (EPS) produced naturally by some lactic acid bacteria can be used as stabilizers in yoghurt. Literature indicates that their properties to bind water and to modulate viscosity are not correlated to EPS concentration but to their structure and interactions with milk proteins. To our knowledge, this is the first work that has studied the effect of combined use of modified starch and EPS in yoghurt. The aim of this work was to study the structure-function relationship of EPS produced in situ by lactic acid bacteria on the rheological/physical properties (gel formation, viscosity, firmness, stiffness) and the microstructure of fermented dairy systems with modified starch. Four starters composed of one strain of Streptococcus thermophilus and one strain of Lactobacillus delbrueckii subsp. bulgaricus and producing EPS with known structure were studied: HC15/210R (control), HC15/291 (neutral, stiff, few branched EPS), HC15/702074 (neutral, flexible, highly branched EPS) and 2104/210R (anionic, stiff, linear, EPS). A final pH of 4.6 was obtained after a fermentation of 180-210 minutes Ă 42 C for all starters. The gel formation process was not influenced by the presence of EPS. The comparison of several EPS of known structure has shown that the anionic EPS from 2104/210R starter improved firmness and viscosity. Neutral, stiff and few branched EPS from HC15/291 starter contributed to viscosity and limited syneresis comparatively to the neutral, flexible and highly branched EPS from HC15/702074 starter. Although the smoothing process had a negative impact on the values of all rheological/physical properties of fermented dairy systems, the functionality of EPS remained. The addition of modified starch improved the rheological/physical properties of stirred fermented dairy systems but had no effect on set fermented dairy systems. To conclude, this work has shown that the rheological/physical properties of fermented dairy systems may be improved by the combination of modified starch and EPS with specific structural characteristics
Caractérisation structurale et fonctionnelle d'AGP31, une glycoprotéine atypique de la paroi chez Arabidopsis thaliana
La paroi cellulaire vĂ©gĂ©tale est une structure dynamique constituĂ©e de rĂ©seaux de polysaccharides et de protĂ©ines dont l'organisation supramolĂ©culaire est complexe. AGP31, codĂ©e par At1g28290, a Ă©tĂ© identifiĂ©e comme une protĂ©ine multi-domaines abondante dans la paroi des cellules des hypocotyles Ă©tiolĂ©s d'Arabidopsis thaliana. Mon travail de thĂšse a consistĂ© Ă Ă©lucider la structure et la fonction d'AGP31. La caractĂ©risation structurale du domaine riche en Pro d'AGP31 a Ă©tĂ© effectuĂ©e : des rĂ©sidus Hyp et des O-galactanes ont Ă©tĂ© localisĂ©s par spectromĂ©trie de masse. AGP31 a Ă©tĂ© trouvĂ©e sous plusieurs glycoformes diffĂ©rant par le type et la taille des O-glycanes et/ou la longueur de la chaĂźne polypeptidique. Des tests in vitro ont montrĂ© des interactions entre diffĂ©rents domaines d'AGP31 et des polysaccharides pariĂ©taux (HG mĂ©thylestĂ©rifiĂ©s, galactanes du RGI). Une remarquable affinitĂ© entre les O-galactanes d'AGP31 et la lectine PNA a Ă©tĂ© montrĂ©e, indiquant de possibles interactions avec des lectines pariĂ©tales. Le patron d'expression d'At1g28290 suggĂšre un rĂŽle de renforcement des parois lors de l'Ă©mergence de la radicule et de l'Ă©longation rapide des hypocotyles Ă©tiolĂ©s. Cependant, l'Ă©tude de plantes ARNi sous-expresseurs et sur-expresseurs d'Atg28290 n'a pas permis de trouver un phĂ©notype au cours du dĂ©veloppement, probablement du fait d'une redondance fonctionnelle avec des gĂšnes proches d'At1g28290. Ce travail constitue la premiĂšre caractĂ©risation structurale d'un domaine riche en Pro d'une protĂ©ine pariĂ©tale et permet de proposer qu'AGP31, via ses diffĂ©rents domaines, interagisse en rĂ©seau dans les parois avec elle-mĂȘme, des polysaccharides ou des lectines.Plant cell wall is a dynamic structure consisting of polysaccharide and protein networks with a complex supramolecular organization. AGP31, encoded by At1g28290, was identified as a abundant multi-domain protein in Arabidopsis thaliana etiolated hypocotyls cell walls. My thesis project consisted in elucidating the structure and the function of AGP31. Structural characterization of the Pro rich domain was performed: Hyp residues and O-galactans were located using mass spectrometry. AGP31 was found as several glycoforms differing by the type and the size of O-glycans as well as by the polypeptidic length. In vitro assays showed interactions between AGP31 domains and cell wall polysaccharides (methylesterified HG, galactans from RGI). A remarkable affinity between AGP31 O-galactans and the PNA lectin was shown, indicating possible interactions with cell wall lectins. The expression pattern of At1128290 suggests a role in cell wall strengthening during radicle emergence and fast elongation of etiolated hypocotyls. However, study of RNAi underexpressors and overexpressors of At1g28290 did not permit to find a phenotype during development, probably because of functional redundancy with At1g28290 homologues. This work constitutes the first structural characterization of a Pro rich domain of a cell wall protein and permits to propose that AGP31, via its different domains, could make scaffolds in the cell wall through interactions with itself, polysaccharides and/or lectins
Recherche de la fonction de protéines riches en hydroxyproline dans les parois végétales
La paroi primaire vĂ©gĂ©tale est une enveloppe dynamique impliquĂ©e dans le dĂ©veloppement ainsi que la rĂ©ponse aux contraintes environnementales. Elle est composĂ©e de rĂ©seaux de polysaccharides et de protĂ©ines dans lesquels interviennent des protĂ©ines multi-domaines de type LRX et des protĂ©ines Ă domaine PAC. Ce travail de thĂšse a consistĂ© Ă rechercher la fonction de ces protĂ©ines dans les parois. Des analyses protĂ©omiques rĂ©alisĂ©es sur des extraits de protĂ©ines pariĂ©tales de racines de plantes sauvages ou mutantes lrx1 d'A. thaliana ont permis d'identifier 424/434 protĂ©ines pariĂ©tales de plantes sauvages/lrx1 respectivement et 25 protĂ©ines candidates pouvant jouer un rĂŽle dans la morphogenĂšse des poils absorbants. Par ailleurs, des protĂ©ines Ă domaine PAC ont Ă©tĂ© identifiĂ©es dans toutes les plantes terrestres Ă©tudiĂ©es. L'apparition des protĂ©ines Ă domaine PAC a pu ĂȘtre associĂ©e Ă la terrestrialisation. Une analyse phylogĂ©nique a permis de grouper les domaines PAC en 10 clades, chacun comportant un domaine PAC d'Amborella trichopoda. Outre les 6 rĂ©sidus Cys caractĂ©risant le domaine PAC, des motifs conservĂ©s ont Ă©tĂ© repĂ©rĂ©s dans les clades, ouvrant la voie pour des Ă©tudes fonctionnelles. Des tests in vitro ont montrĂ© que les domaines PAC interagissent avec diffĂ©rents types de polysaccharides pariĂ©taux et permis de dĂ©finir trois types de spĂ©cificitĂ© vis-Ă -vis de polysaccharides tels que les Ă(1,4) galactanes/RGI, les mannanes, les xyloglucanes et/ou la cellulose. Un nouveau modĂšle d'interactions supramolĂ©culaires dans les parois vĂ©gĂ©tales faisant intervenir des protĂ©ines Ă domaine PAC et des polysaccharides pariĂ©taux a Ă©tĂ© proposĂ©The plant primary cell wall is a dynamic envelope involved in development and in response to environmental constraints. It is composed of networks of polysaccharides and proteins to which multi-domain proteins like LRX (Leucine-Rich repeat Extensin) and PAC (Proline-rich Arabinogalactan Protein Cys-containing) domain proteins contribute. This work aimed at finding partners of such proteins in cell walls using different experimental approaches. Proteomics analyses have been performed on proteins extracted from cell walls of roots of wild type or lrx1 plants. They have allowed the identification of 424/434 cell wall proteins of wild type/lrx1 roots respectively as well as of 25 candidate proteins which could play a role in root hair morphogenesis. Besides, PAC domain proteins have been identified in all the studied terrestrial plants using a bioinformatic approach. The appearance of PAC domain proteins could be associated to terrestrialisation. A phylogenic analysis has allowed to group PAC domains in 10 clades, each of them containing a PAC domain of Amborella trichopoda, an ancestor of angiosperms. In addition to the 6 Cys residues which define the PAC domain, conserved motifs have been identified in each clade. This finding opens the way to functional studies. In vitro tests have shown that the PAC domains could interact with different kinds of cell wall polysaccharides. Three types of specificity could be defined towards Ă(1,4) galactans/RGI, mannans, xyloglucans and/or cellulose. A new model of molecular interactions in plant cell walls including PAC domain proteins and polysaccharides has been propose