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Papers by Julie Bouckaert

The Plant Cell

Polygalacturonases (PGs) fine-tune pectins to modulate cell wall chemistry and mechanics, impacti... more Polygalacturonases (PGs) fine-tune pectins to modulate cell wall chemistry and mechanics, impacting plant development. The large number of PGs encoded in plant genomes leads to questions on the diversity and specificity of distinct isozymes. Herein, we report the crystal structures of 2 Arabidopsis thaliana PGs, POLYGALACTURONASE LATERAL ROOT (PGLR), and ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE2 (ADPG2), which are coexpressed during root development. We first determined the amino acid variations and steric clashes that explain the absence of inhibition of the plant PGs by endogenous PG-inhibiting proteins (PGIPs). Although their beta helix folds are highly similar, PGLR and ADPG2 subsites in the substrate binding groove are occupied by divergent amino acids. By combining molecular dynamic simulations, analysis of enzyme kinetics, and hydrolysis products, we showed that these structural differences translated into distinct enzyme–substrate dynamics and enzyme processivities: ADP...

International Journal of Biological Macromolecules

Pectins, complex polysaccharides and major components of the plant primary cell wall, can be degr... more Pectins, complex polysaccharides and major components of the plant primary cell wall, can be degraded by pectate lyases (PLs). PLs cleave glycosidic bonds of homogalacturonans (HG), the main pectic domain, by β-elimination, releasing unsaturated oligogalacturonides (OGs). To understand the catalytic mechanism and structure/function of these enzymes, we characterized VdPelB fromVerticillium dahliae, a plant pathogen. We first solved the crystal structure of VdPelB at 1.2Å resolution showing that it is a right-handed parallel β-helix structure. Molecular dynamics (MD) simulations further highlighted the dynamics of the enzyme in complex with substrates that vary in their degree of methylesterification, identifying amino acids involved in substrate binding and cleavage of non-methylesterified pectins. We then biochemically characterized wild type and mutated forms of VdPelB. VdPelB was most active on non-methylesterified pectins, at pH 8 in presence of Ca2+ions. VdPelB-G125R mutant was...

The fine-tuning of pectins by polygalacturonases (PGs) plays a key role in modulating plant cell ... more The fine-tuning of pectins by polygalacturonases (PGs) plays a key role in modulating plant cell wall chemistry and mechanics, impacting plant development. The high number of plant PG isoforms and their absence of inhibition by endogenous PG-Inhibiting Proteins (PGIPs) question the regulation of pectin depolymerization during development. Our understanding of the diversity and of the regulation of plant PGs has been impaired by the lack of protein structures. Here we resolved the crystal structures of two PGs from Arabidopsis, PGLR and ADPG2, whose expression overlap in roots. By combining molecular dynamic simulations, analysis of enzymes kinetics and hydrolysis products we determined why plant PGs are not inhibited by PGIPs. We further showed that subtle differences in PGLR and ADPG2 structures translated into distinct dynamics and processivities, leading to peculiar effects on root development, as determined by exogenous applications of enzymes.

Molecular Microbiology, Nov 25, 2004

Mannose-binding type 1 pili are important virulence factors for the establishment of Escherichia ... more Mannose-binding type 1 pili are important virulence factors for the establishment of Escherichia coli urinary tract infections (UTIs). These infections are initiated by adhesion of uropathogenic E. coli to uroplakin receptors in the uroepithelium via the FimH adhesin located at the tips of type 1 pili. Blocking of bacterial adhesion is able to prevent infection. Here, we provide for the first time binding data of the molecular events underlying type 1 fimbrial adherence, by crystallographic analyses of the FimH receptor binding domains from a uropathogenic and a K-12 strain, and affinity measurements with mannose, common monoand disaccharides, and a series of alkyl and aryl mannosides. Our results illustrate that the lectin domain of the FimH adhesin is a stable and functional entity and that an exogenous butyl a a a aD -mannoside, bound in the crystal structures, exhibits a significantly better affinity for FimH (K d = 0.15 m m m m M) than mannose (K d = 2.3 m m m m M). Exploration of the binding affinities of a a a aD -mannosides with longer alkyl tails revealed affinities up to 5 nM. Aryl mannosides and fructose can also bind with high affinities to the FimH lectin domain, with a 100-fold improvement and 15-fold reduction in affinity, respectively, compared with mannose. Taken together, these relative FimH affinities correlate exceptionally well with the relative concentrations of the same glycans needed for the inhibition of adherence of type 1 piliated E. coli. We foresee that our findings will spark new ideas and initiatives for the development of UTI vaccines and anti-adhesive drugs to prevent anticipated and recurrent UTIs.

Pharmaceutics

Selective antiadhesion antagonists of Uropathogenic Escherichia coli (UPEC) type-1 Fimbrial adhes... more Selective antiadhesion antagonists of Uropathogenic Escherichia coli (UPEC) type-1 Fimbrial adhesin (FimH) are attractive alternatives for antibiotic therapies and prophylaxes against acute or recurrent urinary tract infections (UTIs) caused by UPECs. A rational small library of FimH antagonists based on previously described C-linked allyl α-D-mannopyranoside was synthesized using Heck cross-coupling reaction using a series of iodoaryl derivatives. This work reports two new members of FimH antagonist amongst the above family with sub nanomolar affinity. The resulting hydrophobic aglycones, including constrained alkene and aryl groups, were designed to provide additional favorable binding interactions with the so-called FimH “tyrosine gate”. The newly synthesized C-linked glycomimetic antagonists, having a hydrolytically stable anomeric linkage, exhibited improved binding when compared to previously published analogs, as demonstrated by affinity measurement through interactions by Fi...

The presence of β-mannosides in their cell walls confers specific features on the pathogenic yeas... more The presence of β-mannosides in their cell walls confers specific features on the pathogenic yeasts Candida albicans and Candida glabrata compared with non-pathogenic yeasts. In the present study, we investigated the enzymatic properties of Bmt1 (β-mannosyltransferase 1), a member of the recently identified β-mannosyltransferase family, from C. albicans. A recombinant soluble enzyme lacking the N-terminal region was expressed as a secreted protein from the methylotrophic yeast Pichia pastoris. In parallel, functionalized natural oligosaccharides isolated from Saccharomyces cerevisiae and a C. albicans mutant strain, as well as synthetic α-oligomannosides, were prepared and used as potential acceptor substrates. Bmt1p preferentially utilizes substrates containing linear chains of α-1,2-linked mannotriose or mannotetraose. The recombinant enzyme consecutively transfers two mannosyl units on to these acceptors, leading to the production of α-mannosidase-resistant oligomannosides. NMR e...

with specic help available everywhere you see the i O symbol. The following versions of software ... more with specic help available everywhere you see the i O symbol. The following versions of software and data (see references i O) were used in the production of this report:

Joint glycobiology …, 2010

Post-weaning diarrhoea and oedema disease are serious infectious diseases of piglets caused by pa... more Post-weaning diarrhoea and oedema disease are serious infectious diseases of piglets caused by pathogenic E. coli strains, including enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC). These strains account for substantial economical losses in the pig industry ...

Acta Crystallographica Section D Structural Biology

Human myeloperoxidase (MPO) utilizes hydrogen peroxide to oxidize organic compounds and as such p... more Human myeloperoxidase (MPO) utilizes hydrogen peroxide to oxidize organic compounds and as such plays an essential role in cell-component synthesis, in metabolic and elimination pathways, and in the front-line defence against pathogens. Moreover, MPO is increasingly being reported to play a role in inflammation. The enzymatic activity of MPO has also been shown to depend on its glycosylation. Mammalian MPO crystal structures deposited in the Protein Data Bank (PDB) present only a partial identification of their glycosylation. Here, a newly obtained crystal structure of MPO containing four disulfide-linked dimers and showing an elaborate collection of glycans is reported. These are compared with the glycans identified in proteomics studies and from 18 human MPO structures available in the PDB. The crystal structure also contains bound paroxetine, a blocker of serotonin reuptake that has previously been identified as an irreversible inhibitor of MPO, in the presence of thiocyanate, a ...

The Plant Cell

Polygalacturonases (PGs) fine-tune pectins to modulate cell wall chemistry and mechanics, impacti... more Polygalacturonases (PGs) fine-tune pectins to modulate cell wall chemistry and mechanics, impacting plant development. The large number of PGs encoded in plant genomes leads to questions on the diversity and specificity of distinct isozymes. Herein, we report the crystal structures of 2 Arabidopsis thaliana PGs, POLYGALACTURONASE LATERAL ROOT (PGLR), and ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE2 (ADPG2), which are coexpressed during root development. We first determined the amino acid variations and steric clashes that explain the absence of inhibition of the plant PGs by endogenous PG-inhibiting proteins (PGIPs). Although their beta helix folds are highly similar, PGLR and ADPG2 subsites in the substrate binding groove are occupied by divergent amino acids. By combining molecular dynamic simulations, analysis of enzyme kinetics, and hydrolysis products, we showed that these structural differences translated into distinct enzyme–substrate dynamics and enzyme processivities: ADP...

International Journal of Biological Macromolecules

Pectins, complex polysaccharides and major components of the plant primary cell wall, can be degr... more Pectins, complex polysaccharides and major components of the plant primary cell wall, can be degraded by pectate lyases (PLs). PLs cleave glycosidic bonds of homogalacturonans (HG), the main pectic domain, by β-elimination, releasing unsaturated oligogalacturonides (OGs). To understand the catalytic mechanism and structure/function of these enzymes, we characterized VdPelB fromVerticillium dahliae, a plant pathogen. We first solved the crystal structure of VdPelB at 1.2Å resolution showing that it is a right-handed parallel β-helix structure. Molecular dynamics (MD) simulations further highlighted the dynamics of the enzyme in complex with substrates that vary in their degree of methylesterification, identifying amino acids involved in substrate binding and cleavage of non-methylesterified pectins. We then biochemically characterized wild type and mutated forms of VdPelB. VdPelB was most active on non-methylesterified pectins, at pH 8 in presence of Ca2+ions. VdPelB-G125R mutant was...

The fine-tuning of pectins by polygalacturonases (PGs) plays a key role in modulating plant cell ... more The fine-tuning of pectins by polygalacturonases (PGs) plays a key role in modulating plant cell wall chemistry and mechanics, impacting plant development. The high number of plant PG isoforms and their absence of inhibition by endogenous PG-Inhibiting Proteins (PGIPs) question the regulation of pectin depolymerization during development. Our understanding of the diversity and of the regulation of plant PGs has been impaired by the lack of protein structures. Here we resolved the crystal structures of two PGs from Arabidopsis, PGLR and ADPG2, whose expression overlap in roots. By combining molecular dynamic simulations, analysis of enzymes kinetics and hydrolysis products we determined why plant PGs are not inhibited by PGIPs. We further showed that subtle differences in PGLR and ADPG2 structures translated into distinct dynamics and processivities, leading to peculiar effects on root development, as determined by exogenous applications of enzymes.

Molecular Microbiology, Nov 25, 2004

Mannose-binding type 1 pili are important virulence factors for the establishment of Escherichia ... more Mannose-binding type 1 pili are important virulence factors for the establishment of Escherichia coli urinary tract infections (UTIs). These infections are initiated by adhesion of uropathogenic E. coli to uroplakin receptors in the uroepithelium via the FimH adhesin located at the tips of type 1 pili. Blocking of bacterial adhesion is able to prevent infection. Here, we provide for the first time binding data of the molecular events underlying type 1 fimbrial adherence, by crystallographic analyses of the FimH receptor binding domains from a uropathogenic and a K-12 strain, and affinity measurements with mannose, common monoand disaccharides, and a series of alkyl and aryl mannosides. Our results illustrate that the lectin domain of the FimH adhesin is a stable and functional entity and that an exogenous butyl a a a aD -mannoside, bound in the crystal structures, exhibits a significantly better affinity for FimH (K d = 0.15 m m m m M) than mannose (K d = 2.3 m m m m M). Exploration of the binding affinities of a a a aD -mannosides with longer alkyl tails revealed affinities up to 5 nM. Aryl mannosides and fructose can also bind with high affinities to the FimH lectin domain, with a 100-fold improvement and 15-fold reduction in affinity, respectively, compared with mannose. Taken together, these relative FimH affinities correlate exceptionally well with the relative concentrations of the same glycans needed for the inhibition of adherence of type 1 piliated E. coli. We foresee that our findings will spark new ideas and initiatives for the development of UTI vaccines and anti-adhesive drugs to prevent anticipated and recurrent UTIs.

Pharmaceutics

Selective antiadhesion antagonists of Uropathogenic Escherichia coli (UPEC) type-1 Fimbrial adhes... more Selective antiadhesion antagonists of Uropathogenic Escherichia coli (UPEC) type-1 Fimbrial adhesin (FimH) are attractive alternatives for antibiotic therapies and prophylaxes against acute or recurrent urinary tract infections (UTIs) caused by UPECs. A rational small library of FimH antagonists based on previously described C-linked allyl α-D-mannopyranoside was synthesized using Heck cross-coupling reaction using a series of iodoaryl derivatives. This work reports two new members of FimH antagonist amongst the above family with sub nanomolar affinity. The resulting hydrophobic aglycones, including constrained alkene and aryl groups, were designed to provide additional favorable binding interactions with the so-called FimH “tyrosine gate”. The newly synthesized C-linked glycomimetic antagonists, having a hydrolytically stable anomeric linkage, exhibited improved binding when compared to previously published analogs, as demonstrated by affinity measurement through interactions by Fi...

The presence of β-mannosides in their cell walls confers specific features on the pathogenic yeas... more The presence of β-mannosides in their cell walls confers specific features on the pathogenic yeasts Candida albicans and Candida glabrata compared with non-pathogenic yeasts. In the present study, we investigated the enzymatic properties of Bmt1 (β-mannosyltransferase 1), a member of the recently identified β-mannosyltransferase family, from C. albicans. A recombinant soluble enzyme lacking the N-terminal region was expressed as a secreted protein from the methylotrophic yeast Pichia pastoris. In parallel, functionalized natural oligosaccharides isolated from Saccharomyces cerevisiae and a C. albicans mutant strain, as well as synthetic α-oligomannosides, were prepared and used as potential acceptor substrates. Bmt1p preferentially utilizes substrates containing linear chains of α-1,2-linked mannotriose or mannotetraose. The recombinant enzyme consecutively transfers two mannosyl units on to these acceptors, leading to the production of α-mannosidase-resistant oligomannosides. NMR e...

with specic help available everywhere you see the i O symbol. The following versions of software ... more with specic help available everywhere you see the i O symbol. The following versions of software and data (see references i O) were used in the production of this report:

Joint glycobiology …, 2010

Post-weaning diarrhoea and oedema disease are serious infectious diseases of piglets caused by pa... more Post-weaning diarrhoea and oedema disease are serious infectious diseases of piglets caused by pathogenic E. coli strains, including enterotoxigenic E. coli (ETEC) and Shiga toxin-producing E. coli (STEC). These strains account for substantial economical losses in the pig industry ...

Acta Crystallographica Section D Structural Biology

Human myeloperoxidase (MPO) utilizes hydrogen peroxide to oxidize organic compounds and as such p... more Human myeloperoxidase (MPO) utilizes hydrogen peroxide to oxidize organic compounds and as such plays an essential role in cell-component synthesis, in metabolic and elimination pathways, and in the front-line defence against pathogens. Moreover, MPO is increasingly being reported to play a role in inflammation. The enzymatic activity of MPO has also been shown to depend on its glycosylation. Mammalian MPO crystal structures deposited in the Protein Data Bank (PDB) present only a partial identification of their glycosylation. Here, a newly obtained crystal structure of MPO containing four disulfide-linked dimers and showing an elaborate collection of glycans is reported. These are compared with the glycans identified in proteomics studies and from 18 human MPO structures available in the PDB. The crystal structure also contains bound paroxetine, a blocker of serotonin reuptake that has previously been identified as an irreversible inhibitor of MPO, in the presence of thiocyanate, a ...