Acid-base disturbances have serious clinical consequences and are particularly critical in patients whose cardiopulmonary function is compromised. Cellular transport of NH3 and NH4+ has important physiological significance in the regulation of acid-base balance. In the kidney, production and excretion of NH3/NH4+ is critical for net acid excretion. Recently, two non-erythroid glycoproteins (Rhbg and Rhcg) belonging to the Rh family were suggested to be involved in NH3/NH4+ transport. Thus far, the functional properties of these membrane proteins as transport mechanisms are not resolved. In this study, we expressed Rh proteins in Xenopus oocytes and demonstrated that they transport both NH4+ and NH3. As such, the Rh transporters are unique in being able to transport both the ionic and the neutral gaseous components of ammonia. Previous studies have shown that DIDS, a stilbene derivative known to inhibit anion exchangers, was shown to inhibit CO2 transport by AQP1. This led us to hypothesize that DIDS might also inhibit transport of other gases such as NH3 by Rh proteins. We therefore conducted the present study to test the effects of DIDS on NH4+ and NH3 transport by Rh glycoproteins. To do so we used ion-selective microelectrodes and two-electrode voltage clamp to measure changes in surface pH (pHs) and whole cell currents (I) induced by NH3/NH4+ and methyl ammonium (MA/MA+) with or without DIDS. All experiments were conducted in Xenopus oocytes expressing Rhbg. Rhbg was expressed by injecting the oocytes with cRNA of the cloned genes. Control oocytes were injected with H2O. Our results indicate that in oocytes expressing Rhbg, exposure to 5mM NH4Cl (NH3/NH4+) caused a decrease in surface pH (pHs) and an inward current. The decrease in pHs is caused by NH3 influx whereas the inward current is due to electrogenic NH4+ influx. In the presence of DIDS, exposure to 5mM NH4Cl caused a significantly smaller decrease in pHs and current. The %inhibition of pHs and ΔI were 33% and 49%, respectively (P<0.05). Similarly, exposing oocytes expressing Rhbg to 5mM MA/MA+ (a substitute to NH3/NH4+) caused a decrease in pHs and an inward current. In the presence of DIDS, the MA/MA+ induced changes in pHs and current were also inhibited (37% and 63%, respectively; P<0.05). DIDS had no effect on NH3/NH4+ transport in H2O-injected oocytes (not expressing Rhbg). In summary, our data support the following conclusions: 1) RhAG and Rhbg transport both the ionic NH4+ and the neutral NH3 species. 2) Transport of NH4+ is electrogenic. 3) RhAG and Rhbg expression both enhance MA transport, an electroneutral component. 4) Like Rhbg, RhAG also transports MA+, an electrogenic component. The charged MA+ seems to be a direct substrate for RhAG whose transport likely resembles that of NH4 +. 5) Rhcg is likely to be a predominantly NH3 transporter. 6) RhAG and Rhbg are unlikely to be NH4 +/H+ exchangers. Regarding the effect of DIDS, our data also indicate that 1) DIDS partially inhibits the transport of NH3 and MA by Rhbg without affecting endogenous NH3 and MA transport. 2) DIDS also inhibits the electrogenic transport of NH4 + and MA+ by Rhbg. 3) DIDS is the only inhibitor shown to block both gas (NH3) and ionic (NH4 +) transport by Rhbg. / acase@tulane.edu

Proteins of the conserved Mep-Amt-Rh superfamily, including mammalian Rhesus factors,<p>mediate ammonium transport. Ammonium is an important nitrogen source for the<p>biosynthesis of amino acids for instance but its accumulation is also known as cytotoxic in<p>animals. Nevertheless, the controlled disposal of ammonium in urine plays a critical role in<p>the regulation of the acid-base homeostasis. Alteration in ammonium transport via human Rh<p>proteins could have clinical outcomes. In this work, we addressed aspects of structurefunction<p>analysis of altered human Rhesus proteins using a heterologous expression system<p>and further characterized aspects of the patho-physiological roles of Rh proteins using<p>knockout mice models available in the laboratory.<p>Using a yeast-based expression assay, we characterized human Rh variants resulting from non<p>synonymous single nucleotide polymorphisms (nsSNPs) with known or unknown clinical<p>phenotypes. The HsRhAG variants (I61R, F65S) associated to overhydrated hereditary<p>stomatocytosis (OHSt), a disease affecting erythrocytes, proved affected in intrinsic<p>bidirectional ammonium transport, suggesting altered ammonium transport as a potential<p>hallmark of the disease. Moreover, these variants showed trans-dominant negative effects on<p>the activity of their native HsRhAG counterpart, suggesting altered cooperation of the<p>subunits in “heteromeric” transport complexes. On the other hand, we revealed that the<p>R202C variant of HsRhCG, the orthologue of mouse Rhcg required for optimal urinary<p>ammonium excretion and blood pH control, shows an impaired inherent ammonium transport<p>activity. HsRhCGR202C may potentially confer susceptibility to disorders leading to metabolic<p>acidosis for instance. <p>MmRhcg has been shown to be expressed in the male mice epididymal tract, its absence<p>leading to a more acidic luminal fluid and to a reduced male fertility. Using mice<p>models, we further investigated the role of Rhcg and Rhbg proteins in the male<p>reproductive function. <p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

The dimorphic transition from the yeast to the filamentous form of growth allows cells to explore their environment for more suitable niches and is often crucial for the virulence of pathogenic fungi. In contrast to their Mep1/3 paralogues, fungal Mep2-type ammonium transport proteins of the conserved Mep-Amt-Rh family have been assigned an additional receptor role required to trigger the filamentation signal in response to ammonium scarcity. Here, genetic, kinetic, expression and structure-function analyses were used to shed light on the poorly characterized signaling role of Saccharomyces cerevisiae Mep2. We show that Mep2 variants lacking the C-terminal tail conserve the ability to induce filamentation, revealing that signaling can proceed in the absence of exclusive binding of putative partners to the largest cytosolic domain of the protein. Our data support that filamentation signaling requires the conformational changes accompanying substrate translocation through the pore crossing the hydrophobic core of Mep2. pHluorin reporter assays show that the transport activity of Mep2 and of non-signaling Mep1 differently affect yeast cytosolic pH in vivo, and that the unique pore variant Mep2H194E, with apparent uncoupling of transport and signaling functions, acquires increased ability of acidification. Functional characterization in Xenopus oocytes reveals that Mep2 mediates electroneutral substrate translocation while Mep1 performs electrogenic transport. Our findings highlight that the Mep2-dependent filamentation induction is connected to its specific transport mechanism, suggesting a role of pH in signal mediation. We also show that the signaling process is conserved for the Mep2 protein from the human pathogen Candida albicans. Our results allow to propose a model for the sensing function of Mep2 where pH and calcium are key players. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

While ammonium is an excellent nitrogen source for microorganisms and plants, it is known as acytotoxic metabolite and for its critical role in acid/base homeostasis in animals. Ammonium transportinside the cells is ensured by proteins of the Mep-Amt-Rh superfamily, which are conserved frombacteria to humans.The main objective of the thesis is to refine the understanding of the regulation of the three ammoniumtransport proteins Mep1, Mep2 and Mep3 from Saccharomyces cerevisiae. The three Mep proteins areregulated by the Npr1 kinase and the conserved TORC1 signaling pathway. While the activity of Mep2is regulated by phosphorylation of the C-terminal 457 serine, the activity of Mep1 and Mep3 is inhibitedby the factor Amu1 / Par32. In the presence of a poor nitrogen source, Npr1 induces phosphorylation ofAmu1 which appears mainly cytosolic and, Mep1 and Mep3 are active. On the other hand, in thepresence of a good nitrogen source, the activity of TORC1 induces the inhibition of Npr1 and thereforethe dephosphorylation of Amu1 which accumulates at the cell surface and inactivates Mep1 and Mep3.In order to further study the regulation of Mep1 / 3, a genetic screen was performed to isolate suppressorsrecovering Mep1-dependent ammonium transport in the absence of Npr1. Several mutations, insertionsand deletions have been identified in the MEP1 and AMU1 genes allowing Mep1 to be activeindependently of Npr1. This work shows that all the point mutations in Mep1 delimit an area at theinterface between the hydrophobic body of Mep1 and the cytosol, and that part of the C-terminus (CTR)is required for optimal activity of Mep1 but appears dispensable for regulation by Amu1 and Npr1. Thegenetic screen also shows that the last 15 amino acids of Amu1 are required to inactivate Mep1. Finally,the isolation of suppressors showing no mutation in MEP1 and AMU1 could reveal new factors involvedin the control of Mep1.The results indicate that Mep1 is inactivated in the presence of glutamine, a good source of nitrogen,and that this inactivation requires Amu1. The glutamine-dependent inactivation of Mep2 was alsostudied in this manuscript. Mass spectrometry analysis revealed putative phosphorylation sites in CTRspecific to the presence or absence of glutamine.This work also addressed the role of Amu1 in the reactivation function of TORC1 after treatment withrapamycin, in particular by confirming that it requires the function of Mep1/3. The study leads to thehypothesis that the transport mechanism specific to Mep1 and Mep3 and different from Mep2 isinvolved in this function.Finally, in order to better understand the mechanisms of regulation and transport of Mep-Amt-Rhproteins, the experimental determination of the three-dimensional structure of different variants ofMep2, in open or closed conformation, and of Mep1 was undertaken. Throughout this work, thecharacterized Mep1 or Mep2 variants were analyzed in silico by using the available three-dimensionalstructures. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

L'azote est l'un des éléments les plus essentiels dans le monde pour les êtres vivants, car il est essentiel pour la production des éléments de base de la cellule, les acides aminés, les acides nucléiques et les autres constituants cellulaires. L’atmosphère est composé de 78% d'azote gazeux, une source d'azote inutilisable par la plupart des organismes à l'exception de ceux qui possèdent l’enzyme nitrogénase, tels que les bactéries diazotrophique. Ces micro-organismes sont capables de convertir l'azote atmosphérique en ammoniac (NH3), qui est l'une des sources d'azote les plus préférables. Cette réaction exigeant l’ATP, appelée fixation de l'azote, est catalysée par une enzyme, nitrogénase, qui est l'enzyme la plus importante dans le cycle de l'azote. Certaines protéines sont des régulateurs potentiels de la synthèse de la nitrogénase et de son activité; AmtB, DraT, DraG, les protéines PII, etc.. Dans cette thèse, j'ai effectué diverses expériences afin de mieux comprendre leurs rôles détailés dans Rhodobacter capsulatus. La protéine membranaire AmtB, très répandue chez les archaea, les bactéries et les eucaryotes, est un membre de la famille MEP / Amt / Rh. Les protéines AmtB sont des transporteurs d'ammonium, importateurs d'ammonium externe, et ont également été suggéré d’agir comme des senseurs d'ammonium. Il a été montré que l’AmtB de Rhodobacter capsulatus fonctionne comme un capteur pour détecter la présence d'ammonium externe pour réguler la nitrogénase. La nitrogénase est constituée de deux métalloprotéines nommées MoFe-protéine et Fe-protéine. L'addition d'ammoniaque à une culture R. capsulatus conduit à une série de réactions qui mènent à la désactivation de la nitrogénase, appelé "nitrogénase switch-off". Une réaction critique dans ce processus est l’ajout d’un groupe ADP-ribose à la Fe-protéine par DraT. L'entrée de l'ammoniac dans la cellule à travers le pore AmtB est contrôlée par la séquestration de GlnK. GlnK est une protéine PII et les protéines PII sont des protéines centrales dans la régulation du métabolisme de l'azote. Non seulement la séquestration de GlnK par AmtB est importante dans la régulation nitrogénase, mais la liaison de l'ammonium par AmtB ou de son transport partiel est également nécessaire. Les complexes AmtB-GlnK sont supposés de lier DraG, l’enzyme responsable pour enlever l'ADP-ribose ajouté à la nitrogénase par DraT, ainsi formant un complexe ternaire. Dans cette thèse certains détails du mécanisme de transduction du signal et de transport d'ammonium ont été examinés par la génération et la caractérisation d’un mutant dirigé, RCZC, (D335A). La capacité de ce mutant, ainsi que des mutants construits précédemment, RCIA1 (D338A), RCIA2 (G344C), RCIA3 (H193E) et RCIA4 (W237A), d’effectuer le « switch-off » de la nitrogénase a été mesurée par chromatographie en phase gazeuse. Les résultats ont révélé que tous les résidus d'acides aminés ci-dessus ont un rôle essentiel dans la régulation de la nitrogénase. L’immunobuvardage a également été effectués afin de vérifier la présence de la Fe-protéine l'ADP-ribosylée. D335, D388 et W237 semblent être cruciales pour l’ADP-ribosylation, puisque les mutants RCZC, RCIA1 et RCIA4 n'a pas montré de l’ADP-ribosylation de la Fe-protéine. En outre, même si une légère ADP-ribosylation a été observée pour RCIA2 (G344C), nous le considérons comme un résidu d'acide aminé important dans la régulation de la nitrogénase. D’un autre coté, le mutant RCIA3 (H193E) a montré une ADP-ribosylation de la Fe-protéine après un choc d'ammonium, par conséquent, il ne semble pas jouer un rôle important dans l’ADP-ribosylation. Par ailleurs R. capsulatus possède une deuxième Amt appelé AmtY, qui, contrairement à AmtB, ne semble pas avoir des rôles spécifiques. Afin de découvrir ses fonctionnalités, AmtY a été surexprimée dans une souche d’E. coli manquant l’AmtB (GT1001 pRSG1) (réalisée précédemment par d'autres membres du laboratoire) et la formation des complexes AmtY-GlnK en réponse à l'addition d’ammoniac a été examinée. Il a été montré que même si AmtY est en mesure de transporter l'ammoniac lorsqu'il est exprimé dans E. coli, elle ne peut pass’ associer à GlnK en réponse à NH4 +. / Nitrogen is one of the most vital elements in the world for living creatures since it is essential for the production of the basic building blocks of the cell; amino acids, nucleic acids and other cellular constituents. The atmosphere is 78% nitrogen gas (N2), a source of nitrogen unusable by most organisms except for those possessing the enzyme nitrogenase, such as diazotrophic bacteria species. These microorganisms are capable of converting atmospheric nitrogen to ammonia (NH3), which is one of the most preferable nitrogen sources. This ATP demanding reaction, called nitrogen fixation, is catalysed by the nitrogenase enzyme, which is the most important enzyme in the nitrogen cycle. Some proteins are potential regulators of nitrogenase synthesis and activity; AmtB, DraT, DraG, PII proteins and etc. In this thesis I performed various experiments in order to better understand their roles in Rhodobacter capsulatus, in more detail. The membrane protein AmtB, which is widespread among archaea, bacteria and eukaryotes, is a member of the MEP/Amt/Rh family. The AmtB proteins are ammonium transporters, taking up external ammonium, and have also been suggested to sense the presence of ammonium. It has been shown that in Rhodobacter capsulatus AmtB functions as a sensor for the presence of external ammonium in order to regulate nitrogenase. Nitrogenase consists of two metalloprotein components named MoFe-protein and Fe-protein. The addition of ammonium to R. capsulatus culture medium leads to a series of reactions which result in the deactivation of nitrogenase, called “nitrogenase switch-off”. A critical reaction in this process is one in which DraT adds an ADP-ribose group to the Fe-protein of nitrogenase. The entrance of ammonia through the AmtB pore is regulated by GlnK sequestration. GlnK is a PII protein and PII proteins are one of the central proteins in the regulation of nitrogen metabolism. Not only is GlnK-AmtB sequestration important in nitrogenase regulation, but binding of ammonium by AmtB or its partial transport is also necessary. AmtB-GlnK complexes are thought to bind DraG, which is responsible for removing the ADP-ribose that DraT adds to nitrogenase, to form a ternary complex. In this thesis details of the signal transduction mechanism and ammonium transport were examined by generating and characterizing RCZC, a (D335A) site- directed mutant of AmtB. The ability of this mutant, as well as previously constructed mutants RCIA1 (D338A), RCIA2 (G344C), RCIA3 (H193E) and RCIA4 (W237A), to “switch-off” nitrogenase activity was measured by gas chromatography. The results revealed that all the above amino acid residues have critical roles in nitrogenase regulation. Immunoblotting was also carried out to check the presence of ADP-ribosylated Fe-protein. D335, D388 and W237 seem to be crucial for NifH ADP-ribosylation, since their mutants (RCZC, RCIA1 and RCIA4 respectively) didn't show ADP-ribosylation on Fe-protein. In addition, although a slight ADP-ribosylation was observed for RCIA2 (G344C) we still consider it as an important amino acid residue in this matter whereas the remaining mutant RCIA3 (H193E) showed Fe-protein ADP-ribossylation after an ammonium shock, therefore it doesn't seem to be important in NifH ADP-ribosylation. In addition R. capsulatus possesses a second Amt called AmtY, which in contrast to AmtB, doesn't appear to have any specific roles. In order to find out its functionality, AmtY was overexpressed in an E. coli strain lacking AmtB (GT1001 pRSG1) (which was carried out previously by other lab members) and AmtY-GlnK complex formation in response to ammonium addition was examined. It was shown that even though AmtY is able to take up ammonia when expressed in E. coli it fails to associate with GlnK in response to NH4+.

L'azote est l'un des éléments les plus essentiels dans le monde pour les êtres vivants, car il est essentiel pour la production des éléments de base de la cellule, les acides aminés, les acides nucléiques et les autres constituants cellulaires. L’atmosphère est composé de 78% d'azote gazeux, une source d'azote inutilisable par la plupart des organismes à l'exception de ceux qui possèdent l’enzyme nitrogénase, tels que les bactéries diazotrophique. Ces micro-organismes sont capables de convertir l'azote atmosphérique en ammoniac (NH3), qui est l'une des sources d'azote les plus préférables. Cette réaction exigeant l’ATP, appelée fixation de l'azote, est catalysée par une enzyme, nitrogénase, qui est l'enzyme la plus importante dans le cycle de l'azote. Certaines protéines sont des régulateurs potentiels de la synthèse de la nitrogénase et de son activité; AmtB, DraT, DraG, les protéines PII, etc.. Dans cette thèse, j'ai effectué diverses expériences afin de mieux comprendre leurs rôles détailés dans Rhodobacter capsulatus. La protéine membranaire AmtB, très répandue chez les archaea, les bactéries et les eucaryotes, est un membre de la famille MEP / Amt / Rh. Les protéines AmtB sont des transporteurs d'ammonium, importateurs d'ammonium externe, et ont également été suggéré d’agir comme des senseurs d'ammonium. Il a été montré que l’AmtB de Rhodobacter capsulatus fonctionne comme un capteur pour détecter la présence d'ammonium externe pour réguler la nitrogénase. La nitrogénase est constituée de deux métalloprotéines nommées MoFe-protéine et Fe-protéine. L'addition d'ammoniaque à une culture R. capsulatus conduit à une série de réactions qui mènent à la désactivation de la nitrogénase, appelé "nitrogénase switch-off". Une réaction critique dans ce processus est l’ajout d’un groupe ADP-ribose à la Fe-protéine par DraT. L'entrée de l'ammoniac dans la cellule à travers le pore AmtB est contrôlée par la séquestration de GlnK. GlnK est une protéine PII et les protéines PII sont des protéines centrales dans la régulation du métabolisme de l'azote. Non seulement la séquestration de GlnK par AmtB est importante dans la régulation nitrogénase, mais la liaison de l'ammonium par AmtB ou de son transport partiel est également nécessaire. Les complexes AmtB-GlnK sont supposés de lier DraG, l’enzyme responsable pour enlever l'ADP-ribose ajouté à la nitrogénase par DraT, ainsi formant un complexe ternaire. Dans cette thèse certains détails du mécanisme de transduction du signal et de transport d'ammonium ont été examinés par la génération et la caractérisation d’un mutant dirigé, RCZC, (D335A). La capacité de ce mutant, ainsi que des mutants construits précédemment, RCIA1 (D338A), RCIA2 (G344C), RCIA3 (H193E) et RCIA4 (W237A), d’effectuer le « switch-off » de la nitrogénase a été mesurée par chromatographie en phase gazeuse. Les résultats ont révélé que tous les résidus d'acides aminés ci-dessus ont un rôle essentiel dans la régulation de la nitrogénase. L’immunobuvardage a également été effectués afin de vérifier la présence de la Fe-protéine l'ADP-ribosylée. D335, D388 et W237 semblent être cruciales pour l’ADP-ribosylation, puisque les mutants RCZC, RCIA1 et RCIA4 n'a pas montré de l’ADP-ribosylation de la Fe-protéine. En outre, même si une légère ADP-ribosylation a été observée pour RCIA2 (G344C), nous le considérons comme un résidu d'acide aminé important dans la régulation de la nitrogénase. D’un autre coté, le mutant RCIA3 (H193E) a montré une ADP-ribosylation de la Fe-protéine après un choc d'ammonium, par conséquent, il ne semble pas jouer un rôle important dans l’ADP-ribosylation. Par ailleurs R. capsulatus possède une deuxième Amt appelé AmtY, qui, contrairement à AmtB, ne semble pas avoir des rôles spécifiques. Afin de découvrir ses fonctionnalités, AmtY a été surexprimée dans une souche d’E. coli manquant l’AmtB (GT1001 pRSG1) (réalisée précédemment par d'autres membres du laboratoire) et la formation des complexes AmtY-GlnK en réponse à l'addition d’ammoniac a été examinée. Il a été montré que même si AmtY est en mesure de transporter l'ammoniac lorsqu'il est exprimé dans E. coli, elle ne peut pass’ associer à GlnK en réponse à NH4 +. / Nitrogen is one of the most vital elements in the world for living creatures since it is essential for the production of the basic building blocks of the cell; amino acids, nucleic acids and other cellular constituents. The atmosphere is 78% nitrogen gas (N2), a source of nitrogen unusable by most organisms except for those possessing the enzyme nitrogenase, such as diazotrophic bacteria species. These microorganisms are capable of converting atmospheric nitrogen to ammonia (NH3), which is one of the most preferable nitrogen sources. This ATP demanding reaction, called nitrogen fixation, is catalysed by the nitrogenase enzyme, which is the most important enzyme in the nitrogen cycle. Some proteins are potential regulators of nitrogenase synthesis and activity; AmtB, DraT, DraG, PII proteins and etc. In this thesis I performed various experiments in order to better understand their roles in Rhodobacter capsulatus, in more detail. The membrane protein AmtB, which is widespread among archaea, bacteria and eukaryotes, is a member of the MEP/Amt/Rh family. The AmtB proteins are ammonium transporters, taking up external ammonium, and have also been suggested to sense the presence of ammonium. It has been shown that in Rhodobacter capsulatus AmtB functions as a sensor for the presence of external ammonium in order to regulate nitrogenase. Nitrogenase consists of two metalloprotein components named MoFe-protein and Fe-protein. The addition of ammonium to R. capsulatus culture medium leads to a series of reactions which result in the deactivation of nitrogenase, called “nitrogenase switch-off”. A critical reaction in this process is one in which DraT adds an ADP-ribose group to the Fe-protein of nitrogenase. The entrance of ammonia through the AmtB pore is regulated by GlnK sequestration. GlnK is a PII protein and PII proteins are one of the central proteins in the regulation of nitrogen metabolism. Not only is GlnK-AmtB sequestration important in nitrogenase regulation, but binding of ammonium by AmtB or its partial transport is also necessary. AmtB-GlnK complexes are thought to bind DraG, which is responsible for removing the ADP-ribose that DraT adds to nitrogenase, to form a ternary complex. In this thesis details of the signal transduction mechanism and ammonium transport were examined by generating and characterizing RCZC, a (D335A) site- directed mutant of AmtB. The ability of this mutant, as well as previously constructed mutants RCIA1 (D338A), RCIA2 (G344C), RCIA3 (H193E) and RCIA4 (W237A), to “switch-off” nitrogenase activity was measured by gas chromatography. The results revealed that all the above amino acid residues have critical roles in nitrogenase regulation. Immunoblotting was also carried out to check the presence of ADP-ribosylated Fe-protein. D335, D388 and W237 seem to be crucial for NifH ADP-ribosylation, since their mutants (RCZC, RCIA1 and RCIA4 respectively) didn't show ADP-ribosylation on Fe-protein. In addition, although a slight ADP-ribosylation was observed for RCIA2 (G344C) we still consider it as an important amino acid residue in this matter whereas the remaining mutant RCIA3 (H193E) showed Fe-protein ADP-ribossylation after an ammonium shock, therefore it doesn't seem to be important in NifH ADP-ribosylation. In addition R. capsulatus possesses a second Amt called AmtY, which in contrast to AmtB, doesn't appear to have any specific roles. In order to find out its functionality, AmtY was overexpressed in an E. coli strain lacking AmtB (GT1001 pRSG1) (which was carried out previously by other lab members) and AmtY-GlnK complex formation in response to ammonium addition was examined. It was shown that even though AmtY is able to take up ammonia when expressed in E. coli it fails to associate with GlnK in response to NH4+.

Les reins jouent un rôle majeur dans la régulation de l'homéostasie acide-base. La production et l'excrétion rénale d'ammonium assurent environ deux tiers de l'excrétion nette d'acides dans les conditions normales et jusqu'à 90% en situation d'acidose métabolique. Bien que l'excrétion d'ammonium soit un processus finement régulé et capital au maintien de l'équilibre acido-basique, à ce jour aucun transporteur spécifique d'ammonium n'a été décrit chez les mammifères. Les protéines Rhésus Rhcg et Rhbg, membres distants de la famille des transporteurs d'ammonium Mep/Amt, semblaient de bons candidats à cette fonction. L'invalidation du gène Rhcg puis celle de Rhbg ont donc été entreprises chez la souris afin d'estimer leur rôle potentiel dans le transport de l'ammonium. / Doctorat en sciences, Spécialisation biologie moléculaire / info:eu-repo/semantics/nonPublished