β-glicosidases da família 1 das glicosídeo hidrolases (GH 1) são um dos mais importantes grupos de enzimas, estando envolvidas em diversos processos biológicos. Neste trabalho o objetivo principal foi o estudo das bases moleculares da especificidade pelo substrato em β-glicosidases GH 1 utilizando como modelo experimental uma β-glicosidase pertencente a larva de Spodoptera frugiperda (Sfβgli50). Na primeira etapa procurou-se analisar através de mutagênese sítio-dirigida e cinética enzimática o papel na modulação da especificidade pelo substrato e na catálise dos resíduos E190, E194, K201 e M453 da Sfβgli50 , os quais correspondem aos encontrados no sítio de ligação do aglicone das β-glicosidases de milho e de sorgo. Os resultados mostraram que E190 favorece a ligação da porção inicial de aglicones do tipo alquil inicial e também da primeira unidade de glicose de aglicones oligossacarídicos. E194 favorece a ligação de radicais alquil, enquanto K201 é mais relevante para a ligação de unidades de glicose em detrimento de radicais alquil. O balanço entre as interações com E194 e K201 determina a preferência entre unidades de glicose versus radicais alquil. M453 favorece a ligação da segunda unidade de glicose de aglicones oligossacarídicos e também da porção inicial de aglicones do tipo alquil. Nenhum destes resíduos interage com a porção terminal de aglicones do tipo alquil. Demonstrou-se que todos estes resíduos contribuem de forma similar e individualmente fraca na estabilização do complexo ES‡ e suas interações com o aglicone não influenciam na ligação do glicone. Na segunda etapa, procurou-se identificar resíduos ou regiões da Sfβgli50 que participem do processo de modulação da especificidade pelo substrato e que ainda não tivessem sido descritos na literatura. Assim, selecionou-se 14 Sfβgli50 mutantes a partir de uma \"biblioteca\" de mutantes geradas por mutagênese aleatória in vivo. As análises de \"contatos\" e de ligações de hidrogênio envolvendo estes resíduos mutados possibilitaram a identificação de outros resíduos e, consequentemente, a construção de mais 32 Sfβgli50 mutantes. Estas 46 Sfβgli50 mutantes foram produzidas em sistema heterólogo de expressão em bactéria, purificadas e caracterizadas cineticamente. A análise dos resultados obtidos sugere que alguns resíduos mutados devem participar da modulação da especificidade pelo substrato formando \"vias de conexão\", de tal forma que mutações em resíduos que compõem uma \"via\" podem ter efeitos propagados através de suas conexões e, assim, atingirem outras porções da Sfβgli50, como o sítio ativo. Esta propagação pode se dar através de alterações no posicionamento espacial e no conjunto das interações não-covalentes entre os resíduos envolvidos. Finalmente um ponto em comum aos efeitos mutacionais analisados parece ser uma alteração na plataforma basal do glicone, W444, o que causaria modificações na preferência relativa pelos substratos fucosídeos e glucosídeos. / The β-glycosidases of family 1 of the glycoside hydrolases (GH 1) are one of the most important groups of enzymes. These enzymes are involved in a high diversity of physiological functions. The main objective of this study was the analysis of the molecular bases of the specificity for substrate of a β-glycosidase from the larvae of Spodoptera frugiperda (Sfβgli50). Initially the role of residues E190, E194, K201 and M453 of Sfβgli50 in modulation of the specificity for the substrate was investigated through site-directed mutagenesis experiments and enzyme kinetic analysis. These residues corresponds to the those found in the aglycone binding site of Zea mays and Sorghum bicolor β-glycosidases. The results showed that E190 favors the binding of the initial portion of alkyl-type aglycones (up to the sixth methylene group) and also the first glucose unit of oligosaccharidic aglycones, whereas a balance between interactions with E194 and K201 determines the preference for glucose units versus alkyl moieties. E194 favors the binding of alkyl moieties, while K201 is more relevant for the binding of glucose units, in detriment of its favorable interaction with alkyl moieties. In addition, M453 favors the binding of the second glucose unit of oligosaccharidic aglycones and also of the initial portion of alkyl-type aglycones. None of these residues interact with the terminal portion of alkyl-type aglycones. It was also demonstrated that E190, E194, K201 and M453 similarly contribute to stabilize ES‡. Their interactions with aglycone are individually weaker than those formed by residues interacting with glycone, but their joint catalytic effects are similar. Finally, these interactions with aglycone do not influence glycone binding. In the second part of this study, new Sfβgli50 residues or portions that participated in the modulation of the substrate specificity were identified. In order to reach this objective, 14 Sfβgli50 mutants were seleted from a \"library\" generated by random mutagenesis in vivo. Based on the \"contacts\" or hydrogen bounds involving these 14 mutated residues 32 additional mutant Sfβgli50 were constructed. These 46 Sfβgli50 mutant were produced in bacteria, purificated and characterized. The results suggest that these residues ways be grouped in \"connective pathways\", a set of residues that contact each other. Mutations in residues that compose a \"pathways\" may be propagated through its connections reaching the Sfβgli50 active site. This propagation may be mediated by alterations in the spatial positioning and the set of non covalent interactions of these residues. Finally, several of these \"connective pathways\" contact a common point in the active site, the basal platform of the glycone subsite, W444.

<p>Glycosidases hydrolyse the glycosidic bond in carbohydrates. Structural studies of three glycosidases with different substrate specificities are presented in this work.</p><p>Dextranase catalyzes the hydrolysis of <i>α</i>-1,6-glycosidic linkage in dextran polymers. The structure of dextranase, Dex49A, from <i>Penicillium minioluteum</i> was solved in the apo-enzyme (1.8 Å resolution) and product-bound (1.65 Å resolution) forms. The main domain of the enzyme is a right-handed β-helix, which is connected to a β-sandwich domain at the N-terminus. Using NMR spectroscopy the reaction course was shown to occur with net inversion at the anomeric carbon. A new clan is suggested that links glycoside hydrolase (GH) families 28 and 49.</p><p>Endo-<i>β</i>-1,4-D-mannanase catalyzes the depolymerization of <i>β</i>-1,4-mannan polymers. The structure of endo-1,4-<i>β</i>-mannanase Man5A from blue mussel <i>Mytilus edulis</i> has been determined at 1.6 Å resolution. Kinetic analysis of Man5A revealed that the enzyme requires at least 6 subsites for efficient hydrolysis. The architecture of the catalytic cleft differs significantly from other GH 5 enzyme structures. We therefore suggest that Man5A represents a new subfamily in GH 5. </p><p>Both the Dex49A and the Man5A structures were determined by multiple-wavelength anomalous diffraction using the selenium <i>K</i>-edge with selenomethionyl enzymes expressed in the yeast <i>Pichia pastoris</i>.</p><p>Endoglucanase Cel6A from <i>Thermobifida fusca</i> hydrolyzes the <i>β</i>-1,4 linkages in cellulose. The structure of the catalytic domain of Cel6A from <i>T. fusca</i> in complex with a non-hydrolysable substrate analogue has been determined to 1.5 Å resolution. The glycosyl unit in subsite –1 was sterically hindered by Tyr73 and forced into a distorted ²S_O conformation. In the enzyme where Tyr73 was mutated to a serine residue the hindrance was removed and the glycosyl unit in subsite –1 had a relaxed ⁴C₁ chair conformation.</p>

Glycosidases hydrolyse the glycosidic bond in carbohydrates. Structural studies of three glycosidases with different substrate specificities are presented in this work. Dextranase catalyzes the hydrolysis of α-1,6-glycosidic linkage in dextran polymers. The structure of dextranase, Dex49A, from Penicillium minioluteum was solved in the apo-enzyme (1.8 Å resolution) and product-bound (1.65 Å resolution) forms. The main domain of the enzyme is a right-handed β-helix, which is connected to a β-sandwich domain at the N-terminus. Using NMR spectroscopy the reaction course was shown to occur with net inversion at the anomeric carbon. A new clan is suggested that links glycoside hydrolase (GH) families 28 and 49. Endo-β-1,4-D-mannanase catalyzes the depolymerization of β-1,4-mannan polymers. The structure of endo-1,4-β-mannanase Man5A from blue mussel Mytilus edulis has been determined at 1.6 Å resolution. Kinetic analysis of Man5A revealed that the enzyme requires at least 6 subsites for efficient hydrolysis. The architecture of the catalytic cleft differs significantly from other GH 5 enzyme structures. We therefore suggest that Man5A represents a new subfamily in GH 5. Both the Dex49A and the Man5A structures were determined by multiple-wavelength anomalous diffraction using the selenium K-edge with selenomethionyl enzymes expressed in the yeast Pichia pastoris. Endoglucanase Cel6A from Thermobifida fusca hydrolyzes the β-1,4 linkages in cellulose. The structure of the catalytic domain of Cel6A from T. fusca in complex with a non-hydrolysable substrate analogue has been determined to 1.5 Å resolution. The glycosyl unit in subsite –1 was sterically hindered by Tyr73 and forced into a distorted 2SO conformation. In the enzyme where Tyr73 was mutated to a serine residue the hindrance was removed and the glycosyl unit in subsite –1 had a relaxed 4C1 chair conformation.

In this thesis the synthesis of several hydrolytically stable carbohydrate mimics with the potential to function as glycosidase or lectin inhibitors are described. This work is presented in Chapters 2-5. Chapters 2 and 3 describe synthetic efforts for producing carbasugars, and include the first synthesis of 1,2-bis-epi-valienamine and the preparation of two previously known aminocarbasugars. All three compounds were synthesised starting from D-mannose, using ring-closing metathesis as the key step. 1,2-Bis-epi-valienamine was found to inhibit Cellulomonas fimi β-mannosidase with a Ki value of 140 mM. Also included is the development of a novel synthetic route from cheap D-fructose to three mannose-mimicking carbasugars using a ring-closing metathesis strategy. Two of the compounds are potential inhibitors of the FimH adhesin. In Chapters 4 and 5 the synthesis of a number of pseudodisaccharides are presented; valienamine- and epi-valienamine-containing pseudodisaccharides and a small library of S-linked pseudodisaccharides were prepared. Various synthetic strategies were explored, including an alkylation strategy, Mitsunobu couplings, and sulfonate displacements. This is the first report on the synthesis of a valienamine pseudodisaccharide with β-lyxo-configuration. Two of the S-linked pseudodisaccharides were found to bind to Concanavalin A with high affinity. The final chapter (Chapter 6) of this thesis focuses on the development of a carbohydrate epimerisation method using transition metal catalysis. Two equilibrium constants involving gluco/manno- and gluco/allo-alcohols were determined via this method. / At the time od doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 3: Manuscript. Paper 5: Manuscript.

&#946;-glicosidases da família 1 das glicosídeo hidrolases (GH 1) são um dos mais importantes grupos de enzimas, estando envolvidas em diversos processos biológicos. Neste trabalho o objetivo principal foi o estudo das bases moleculares da especificidade pelo substrato em &#946;-glicosidases GH 1 utilizando como modelo experimental uma &#946;-glicosidase pertencente a larva de Spodoptera frugiperda (Sf&#946;gli50). Na primeira etapa procurou-se analisar através de mutagênese sítio-dirigida e cinética enzimática o papel na modulação da especificidade pelo substrato e na catálise dos resíduos E190, E194, K201 e M453 da Sf&#946;gli50 , os quais correspondem aos encontrados no sítio de ligação do aglicone das &#946;-glicosidases de milho e de sorgo. Os resultados mostraram que E190 favorece a ligação da porção inicial de aglicones do tipo alquil inicial e também da primeira unidade de glicose de aglicones oligossacarídicos. E194 favorece a ligação de radicais alquil, enquanto K201 é mais relevante para a ligação de unidades de glicose em detrimento de radicais alquil. O balanço entre as interações com E194 e K201 determina a preferência entre unidades de glicose versus radicais alquil. M453 favorece a ligação da segunda unidade de glicose de aglicones oligossacarídicos e também da porção inicial de aglicones do tipo alquil. Nenhum destes resíduos interage com a porção terminal de aglicones do tipo alquil. Demonstrou-se que todos estes resíduos contribuem de forma similar e individualmente fraca na estabilização do complexo ES&#8225; e suas interações com o aglicone não influenciam na ligação do glicone. Na segunda etapa, procurou-se identificar resíduos ou regiões da Sf&#946;gli50 que participem do processo de modulação da especificidade pelo substrato e que ainda não tivessem sido descritos na literatura. Assim, selecionou-se 14 Sf&#946;gli50 mutantes a partir de uma \"biblioteca\" de mutantes geradas por mutagênese aleatória in vivo. As análises de \"contatos\" e de ligações de hidrogênio envolvendo estes resíduos mutados possibilitaram a identificação de outros resíduos e, consequentemente, a construção de mais 32 Sf&#946;gli50 mutantes. Estas 46 Sf&#946;gli50 mutantes foram produzidas em sistema heterólogo de expressão em bactéria, purificadas e caracterizadas cineticamente. A análise dos resultados obtidos sugere que alguns resíduos mutados devem participar da modulação da especificidade pelo substrato formando \"vias de conexão\", de tal forma que mutações em resíduos que compõem uma \"via\" podem ter efeitos propagados através de suas conexões e, assim, atingirem outras porções da Sf&#946;gli50, como o sítio ativo. Esta propagação pode se dar através de alterações no posicionamento espacial e no conjunto das interações não-covalentes entre os resíduos envolvidos. Finalmente um ponto em comum aos efeitos mutacionais analisados parece ser uma alteração na plataforma basal do glicone, W444, o que causaria modificações na preferência relativa pelos substratos fucosídeos e glucosídeos. / The &#946;-glycosidases of family 1 of the glycoside hydrolases (GH 1) are one of the most important groups of enzymes. These enzymes are involved in a high diversity of physiological functions. The main objective of this study was the analysis of the molecular bases of the specificity for substrate of a &#946;-glycosidase from the larvae of Spodoptera frugiperda (Sf&#946;gli50). Initially the role of residues E190, E194, K201 and M453 of Sf&#946;gli50 in modulation of the specificity for the substrate was investigated through site-directed mutagenesis experiments and enzyme kinetic analysis. These residues corresponds to the those found in the aglycone binding site of Zea mays and Sorghum bicolor &#946;-glycosidases. The results showed that E190 favors the binding of the initial portion of alkyl-type aglycones (up to the sixth methylene group) and also the first glucose unit of oligosaccharidic aglycones, whereas a balance between interactions with E194 and K201 determines the preference for glucose units versus alkyl moieties. E194 favors the binding of alkyl moieties, while K201 is more relevant for the binding of glucose units, in detriment of its favorable interaction with alkyl moieties. In addition, M453 favors the binding of the second glucose unit of oligosaccharidic aglycones and also of the initial portion of alkyl-type aglycones. None of these residues interact with the terminal portion of alkyl-type aglycones. It was also demonstrated that E190, E194, K201 and M453 similarly contribute to stabilize ES&#8225;. Their interactions with aglycone are individually weaker than those formed by residues interacting with glycone, but their joint catalytic effects are similar. Finally, these interactions with aglycone do not influence glycone binding. In the second part of this study, new Sf&#946;gli50 residues or portions that participated in the modulation of the substrate specificity were identified. In order to reach this objective, 14 Sf&#946;gli50 mutants were seleted from a \"library\" generated by random mutagenesis in vivo. Based on the \"contacts\" or hydrogen bounds involving these 14 mutated residues 32 additional mutant Sf&#946;gli50 were constructed. These 46 Sf&#946;gli50 mutant were produced in bacteria, purificated and characterized. The results suggest that these residues ways be grouped in \"connective pathways\", a set of residues that contact each other. Mutations in residues that compose a \"pathways\" may be propagated through its connections reaching the Sf&#946;gli50 active site. This propagation may be mediated by alterations in the spatial positioning and the set of non covalent interactions of these residues. Finally, several of these \"connective pathways\" contact a common point in the active site, the basal platform of the glycone subsite, W444.

Este trabalho procurou avaliar algumas isozimas envolvidas com o processo de degradação de polissacarídeos da parede celular vegetal, encontradas em Aspergillus versicolor, fungo pertencente a um gênero onde a multiplicidade de componentes enzimáticos com a mesma atividade oscila de uma a três. Duas ß-xilosidases foram purificadas por meio de DEAE-celulose e precipitação com sulfato de amônia. Ambas mostraram-se enzimas que, quando deglicosiladas por PNGaseF, apresentam mesmos mapas trípticos. A glicosilação mostrou-se importante para a manifestação de diferenças bioquímicas relacionadas às interações com ambiente eletrolítico adjacente, visto as mudanças das curvas de pH e alterações de comportamento frente a sais de íons metálicos, tão bem como para a manutenção do funcionamento das enzimas. Também foi verificado que as diferentes formas glicosiladas periplásmicas são produzidas em meios distintos (xilana e xilose), cujos pH finais corresponderam aos pH das enzimas encontradas. Por meio de zimogramas, verificou-se que estas não eram produzidas de imediato, mas selecionadas ao longo do tempo de cultivo. Esta seleção foi inicialmente independente do pH, visto este, mesmo tamponado, ser corrigido pelo fungo, de modo a se apresentar, ao final de 48h, correlato com o da enzima selecionada. Exame cromatográfico em Concanavalina-A das enzimas deglicosiladas por EndoH mostraram que a oriunda de xilana tem aporte maior de ramificações biantenárias, que são ricas em galactose. Ambas apresentaram mapas trípticos iguais. A ß-xilosidase induzida por xilana apresentou proporções de manose, galactose e glucose iguais a 69,68 : 30,25 : 0,056 %, respectivamente, enquanto que ß-xilosidase induzida por xilose apresentou proporções iguais a 85,35 : 14,54 : 0,094%, respectivamente, resultado que corrobora com a resultado anterior. Duas ß-glucosidases de superfície micelial foram purificadas por meio de DEAE-Sephacel e DEAE-celulose. Ambas mostraram-se mais semelhantes entre si que as ß-xilosidases, e independentes de fonte de carbono ou pH. No entanto, apresentaram diferenças frente à inibição por celobiose (acentuada a partir de 10mM para ß-glucosidase I e 20mM para B-glucosidase II) e, embora sutis, a pH. Após serem submetidas a 45 ºC por 30min (temperatura que induziu segunda conformação estável) mostraram curvas de pH muito distintas, que foram eliminadas nas enzimas submetidas ao mesmo experimento após deglicosilação por PNGaseF. Ambas apresentaram mapas trípticos iguais. A ß-glucosidase I mostrou-se constituída de Man:Gal:Glu em proporções iguais a 78,36%:21,61%:0,033% do carboidrato total, respectivamente, e a ß-glucosidase II, Man:Gal:Glu iguais a 83,59%:16,38%:0,028%, respectivamente. Ambas também apresentaram sinergismo quando juntas. Sobre celobiose, foi verificado apenas em pH acima de 5.5. Sobre celooligossacarídeos, manifestou-se em pH 5,25. A ß-glucosidase I foi menos ativa que a ß-glucosidase II quando em ausência de glucose e celobiose na solução de reação inicial, situação na qual o contrário foi verdadeiro. O sinergismo foi drasticamente eliminado após deglicosilação por PNGaseF. Não se sabe se este resultado foi oriundo de mudanças cinéticas provocadas pela deglicosilação ou de uma possível eliminação de agregação anteriormente existente entre glicosiladas. O componente ß-glicosidásico extracelular foi purificado por meio de DEAE-Sephacel e Octyl-Sepharose, e se revelou um heteroagregado de fosfatase ácida com ß-glicosidase, que se mostrou estável e ativo em ampla gama de temperaturas e pH, com ótimos de 55ºC e 5,5, respectivamente. Entretanto, os perfis das curvas foram distintos entre as enzimas componentes. Somente concentrações superiores a 0,8mM de cloreto de cobalto apresentaram efeito desagregador, podendo ser empregado em conjunto com DEAE-celulose para purificação das enzimas isoladas. Quando separadas, fosfatase mostrou-se 260% mais ativa e ß-glicosidase, 50% menos ativa. Nesta condição, as faixas de pH se restringiram, acidificando-se, localizando-se entre pH 4,0 e 5,5. Aparentemente, a agregação reforça a atividade celobiásica. Fosfatase foi ativa sobre farelo de trigo e fitato de sódio e adsorveu fortemente em farelo de trigo. ß-glicosidase apresentou atividade sobre farelo de trigo, xilana e Avicel (liberando apenas glicose desta última), revelando-se enzima com atividade celobioidrolásica inespecífica, embora ávida por celobiose. As atividades foram determinadas como oriundas do mesmo sítio catalítico. ß-glicosidase não foi seqüestrada por farelo de trigo quando desagregada, resultado invertido quando reagregada. O seqüestro por farelo de trigo, aparentemente, deveu-se a interações entre sítio catalítico da fosfatase e substrato. / This study explored enzyme multiplicity on hemicelllulose and cellulose degrading systems. It first demonstrates the differences of PNGaseF deglycosylation and EndoH deglycosylation on forms of two ß-glicosidase activities present on surface of mycelia from Aspergillus versicolor grown on several carbon sources. Aspergillus versicolor produces ß-xylosidases with different biochemical properties and different degree of glycosylation, when grown on xylan or xylose. Were investigated the biochemical properties of these ß-xylosidases after deglycosylation. The purified enzymes were deglycosylated with endo-H or PNGase F. After this treatment both enzymes migrated faster in PAGE exhibiting the same Rf. On SDS-PAGE both enzymes showed similar migration. The optima temperature of xylan-induced and xylose-induced ß-xylosidases was 45 ºC and 40 ºC, respectively, and of 35 ºC after deglycosylation. The xylan-induced enzyme was more active at acidic pH than the xylose-induced enzyme. After deglycosylation the optimum pH of both enzymes was 6.0. The thermal resistance of the enzymes at 55 ºC showed a half-life of 15 min and 9 min for xylose-and xylan-induced enzymes, respectively. After deglycosylation both exhibited half-lives of 7.5. Native enzymes exhibited different response to ions, while deglycosylated enzymes exhibited identical sensitivity to ions. Limited proteolysis yielded coincident profiles in SDS-PAGE for both deglycosylated enzymes. All data suggest that the two A.versicolor ß-xylosidases share a common polypeptide core with differential glycosylation, apparently responsible for their biochemical and biophysical differences. Aspergillus versicolor also produced ß-glucosidases with different biochemical properties and different degree of glycosylation independently of carbon source. ß-Glucosidase I differed from ß-glucosidase II principally considering the amount and composition of carbohydrate, sensitivity to ions and pH. The purified enzymes shared the same tripitic maps and molecular masses after deglycosylations. All results showed that the biochemical differences observed for two enzymes were directly linked to PNGaseF- deglycosylation. Considering that Rfs, elution profiles on Con-A and residual glycosylation of both enzymes treated with EndoH or PNGaseF were the same, but differed on the mannose/galactose ratio, we inferred differences on proportion of hybrid-type/high-mannose-type glycans. The significance of this glycoform diversity was stressed in analysis of the action of mixture of both ß-glucosidases on celooligosoccharides and on cellobiose. This synergism was abolished after PNGaseF deglycosylation. These results are the first to show synergism between glycoforms of glycosil-hydrolases, representing a new class of synergistic type. The work also described a new form of aggregation between enzymes. Generally, ß-glycosidases are described as soluble components, attached to cell wall or free in the culture medium. This work verified that it could be extracelular adsorbed to wheat straw when aggregated with an acid phosphatase. The results strongly suggested that phosphatase is the component responsible for the process of adsorption on the substrate. The disaggregation was cobalt mediated, being not observed for another ions. The aggregation state has positive effects on glycosidase activity, extending pH ratio and increasing hydrolysis velocity. The opposite was found to phosphatase activity.

Les premiers iminosucres multivalents rapportés dans la littérature datent de 1999. Depuis, c’est plus d’une centaine de clusters de ce type qui ont été synthétisés et décrits une quarantaine de publications. L’obtention d’un premier effet multivalent fort sur une glycosidase, en 2010, a initié de nouveaux travaux visant à étudier et à comprendre son mécanisme et ses limites. Dans cette optique le présent travail de thèse a exploité plusieurs approches. La première partie décrit la synthèse de dendrons "cliquables" permettant de multiplier par trois ou par neuf la valence initiale des plateformes utilisées. La deuxième est une étude de la synthèse d’espaceurs rigides. La troisième est la préparation de plateformes modulables, des neo-cyclodextrines, pour obtenir un contrôle plus fin de la topologie des clusters. L’association de dendrons "cliquables" et de plateformes cyclopeptoïdes de dimensions contrôlées a abouti à un résultat sans précèdent en termes d’effet multivalent. Ainsi, le cluster 36-valent à ligands DNJ est un inhibiteur 170 000 fois plus fort que l’analogue monovalent correspondant sur l’alpha-mannosidase des pois sabre blanc (Jack Bean). / The first multivalent iminosugars were published in 1999. From this date, it’s more than a hundred of clusters that were synthesized and presented in about forty publications. In 2010, the first strong multivalent effect in glycosidase inhibition was obtained and prompted further studies of its mechanism and its limits. To reach these goals, this PhD work has developed different strategies. The first was to synthesize "clickable" dendrons which can lead to a multiplication of the initial valency of our scaffolds by three or by nine. The second approach was a study to obtain rigid linkers. The third one was the preparation of modular scaffolds, neo-cyclodextrins, in order to finely tune the topology of the resulting clusters. The combination of our "clickable" dendrons with cyclopeptoid scaffolds gave an unprecedented multivalent effect on glycosidase inhibition. The 36-valent DNJ-based cluster is indeed a 170 000-fold more potent inhibitor than the corresponding monovalent control for Jack Bean alpha-mannosidase.

Os artrópodes constituem as formas mais abundantes de vida animal no planeta. O sistema digestivo dos Arthropoda é uma das mais importantes superfícies de contato com o ambiente. Pouco se conhece a respeito do sistema digestivo dos aracnídeos. Identificamos as principais carboidrases digestivas em três Arachnida modelo: Tityus serrulatus, Amblyomma cajennense e Nephilengys cruentata. As &#945;-fucosidases são glicosídeo hidrolases que catalisam a hidrólise de ligações glicosídicas entre uma fucose ligada a outro carboidrato ou outro tipo de molécula. Estas enzimas são fundamentais no processamento de glicoproteínas e glicolipídeos. Observamos altas atividades de &#945;-fucosidases em todas as espécies estudadas e estas enzimas foram isoladas e caracterizadas. / Arthropods are the most abundant animal life form on the planet. The digestive system of Arthropoda is one of the most important areas of contact with the environment. The study of Arachnida digestive enzymes has been sporadic and remains a largely unexplored area. We identified the most important digestive carbohydrases in three Arachnida models: Tityus serrulatus, Amblyomma cajennense and Nephilengys cruentata. The &#945;-fucosidases are glycoside hydrolases that catalyze the hydrolysis of glycosidic links between a fucose linked to other carbohydrate or another type of molecule. These enzymes are essential in the processing of glycoprotein and glycolipids. We showed that all models tested presented high activities of digestive &#945;-fucosidases and these enzymes were isolated and characterized.

No description available.

In the post-genomic era, recognition of the importance of sugars is increasing in biological research. For the precise analysis of their functions, homogeneous materials are required. Chemical synthesis is a powerful tool for preparation of homogeneous oligosaccharides and glycoconjugates. Glycosidases are potent catalysts for this purpose because they realize high stereo- and regio- selectivities under conditions benign to biomolecules without repetitive protection/deprotection procedures. A glycosynthase is an aritificial enzyme which is derived from a glycosidase and is devised for glycosylation reaction. To suppress the mechanistically inherent oligomerization side reaction of this class of biocatalysts, a glycosidase with plastic substrate recognition was engineered to afford the first α-mannosynthase. This novel biocatalyst showed low occurrence of oligomerized products as designed and was applied to prepare a wide range of oligosaccharides. Glycosidases are also valuable tools for glycan engineering of glycoconjugates, which is a pivotal issue in the development of pharmaceutical agents, including immunoglobulin G (IgG)-based drugs. EndoS, an endo-β-N-acetylglucosaminidase from Streptococcus pyogenes, natively cleaves N-glycans on IgG specifically. When the latent glycosylation activity of this enzyme was applied, the N-glycan remodelling of full-length IgG was successfully achieved for the first time and a highly pure glycoform was obtained using the chemically synthesized oxazoline tetrasaccharide as glycosyl donor. This biocatalytic reaction allows development of a novel type of antibody-drug conjugates (ADCs) in which drug molecules are linked to N-glycans site-specifically. For this purpose, glycans with bioorthogonal reaction handles were synthesized and conjugated to IgG. A model reaction using a dye compound as reaction partner worked successfully and the synthetic method for this newly designed ADC was validated. Glycan trimming of glycoproteins expressed from Pichia pastoris was performed using exoglycosidases to derive homogeneous glycoform. Jack Bean α-mannosidase (JBM) trimmed native N-glycans down to the core trisaccharide structure but some of the glycoforms were discovered to be resistant to the JBM activity. Enzymatic analyses using exoglycosidases suggested that the JBM-resistant factor was likely to be β-mannoside. In summary, this work advanced application of modified glycosidases for preparation of oligosaccharides and also demonstrated biocatalytic utility of glycosidases to produce biologically relevant glycoconjugates with homogeneous glycoforms.