I02-Macromolecular Crystallography
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Diamond Proposal Number(s):
[15304]
Abstract: Bacillus subtilis PdaC (BsPdaC) is a membrane-bound, multidomain peptidoglycan N-deacetylase acting on N-acetylmuramic (Mur-NAc) residues and conferring lysozyme resistance to modified cell wall peptidoglycans. BsPdaC contains a C-terminal family 4 carbohydrate esterase (CE4) catalytic domain, but unlike other MurNAc deacetylases, BsPdaC also has GlcNAc deacetylase activity on chitooligosaccharides (COSs), characteristic of chitin deacetylases. To uncover the molecular basis of this dual activity, here we determined the X-ray structure of the BsPdaC CE4 domain at 1.54 Å resolution and analyzed its mode of action on COS substrates. We found that the minimal substrate is GlcNAc3 and that activity increases with the degree of glycan polymerization. COS deacetylation kinetics revealed that BsPdaC operates by a multiple-chain mechanism starting at the internal GlcNAc units and leading to deacetylation of all but the reducing-end GlcNAc residues. Interestingly, BsPdaC shares higher sequence similarity with the peptidoglycan GlcNAc deacetylase SpPgdaA than with other MurNAc deacetylases. Therefore, we used ligand-docking simulations to analyze the dual GlcNAc- and MurNAc-binding specificities of BsPdaC and compared them with those of SpPgdA and BsPdaA, representing peptidoglycan deacetylases highly specific for GlcNAc or MurNAc residues, respectively. BsPdaC retains the conserved Asp–His–His metal-binding triad characteristic of CE4 enzymes acting on GlcNAc residues, differing from MurNAc deacetylases that lack the metal-coordinating Asp residue. BsPdaC contains short loops similar to those in SpPgdA, resulting in an open binding cleft that can accommodate polymeric substrates. We propose that PdaC is the first member of a new subclass of peptidoglycan MurNAc deacetylases.
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Nov 2019
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[15304]
Abstract: Protein aggregate reactivation in metazoans is accomplished by the combined activity of Hsp70, Hsp40 and Hsp110 chaperones. Hsp110s support the refolding of aggregated polypeptides acting as specialized nucleotide exchange factors of Hsp70. We have studied how Apg2, one of the three human Hsp110s, regulates the activity of Hsc70 (HspA8), the constitutive Hsp70 in our cells. Apg2 shows a biphasic behavior: at low concentration, it stimulates the ATPase cycle of Hsc70, binding of the chaperone to protein aggregates and the refolding activity of the system, while it inhibits these three processes at high concentration. When the acidic subdomain of Apg2, a characteristic sequence present in the substrate binding domain of all Hsp110s, is deleted, the detrimental effects occur at lower concentration and are more pronounced, which concurs with an increase in the affinity of the Apg2 mutant for Hsc70. Our data support a mechanism in which Apg2 arrests the chaperone cycle through an interaction with Hsc70(ATP) that might lead to premature ATP dissociation before hydrolysis. In this line, the acidic subdomain might serve as a conformational switch to support dissociation of the Hsc70:Apg2 complex.
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Dec 2018
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[15304]
Abstract: Glycolipids play a central role in a variety of important biological processes in all living organisms. PatA is a membrane acyltransferase involved in the biosynthesis of phosphatidyl-myo-inositol mannosides (PIMs), key structural elements and virulence factors of Mycobacterium tuberculosis. PatA catalyzes the transfer of a palmitoyl moiety from palmitoyl-CoA to the 6-position of the mannose ring linked to the 2-position of inositol in PIM1/PIM2. We report here the crystal structure of PatA in the presence of 6-O-palmitoyl-α-D-mannopyranoside, unraveling the acceptor binding mechanism. The acceptor mannose ring localizes in a cavity at the end of a surface-exposed, long groove where the active site is located, whereas the palmitate moiety accommodates into a hydrophobic pocket deeply buried in the α/β core of the protein. Both fatty acyl chains of the PIM2 acceptor are essential for the reaction to take place, highlighting their critical role in the generation of a competent active site. By the use of combined structural and quantum-mechanics/molecular-mechanics (QM/MM) metadynamics we unravel the catalytic mechanism of PatA at the atomic-electronic level. Our study provides a detailed structural rationale for a stepwise reaction, with the generation of a tetrahedral transition state for the rate-determining step. Finally, the crystal structure of PatA in the presence of β-D-mannopyranose and palmitate suggest an inhibitory mechanism for the enzyme, providing exciting possibilities for inhibitor design and the discovery of chemotherapeutic agents against this major human pathogen.
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Nov 2017
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I04-1-Macromolecular Crystallography (fixed wavelength)
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[15304]
Abstract: Glycosyltransferases (GTs) are a key family of enzymes that catalyses the synthesis of glycosidic bonds in all living organisms. The reaction involves the transfer of a glycosyl moiety and can proceed with retention or inversion of the anomeric configuration. To date, the elucidation of the catalytic mechanism of retaining GTs is of great controversy, particularly for those enzymes containing a putative nucleophilic residue in the active site, for which a double-displacement mechanism has been suggested. Here, we report native ternary complexes of the retaining α1,3-Galactosyltransferase (α3GalT) from Bos taurus - containing such a nucleophile in the active site - in a productive mode for catalysis, in the presence of its sugar donor UDP-Gal, the acceptor substrate lactose, and the divalent cation cofactor. This new experimental evidence supports a front-side substrate-assisted SNi-type reaction for α3GalT, and suggests a conserved common catalytic mechanism among retaining GTs.
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Sep 2017
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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David
Albesa-jove
,
Javier
Romero-garcia
,
Enea
Sancho-vaello
,
F.-xabier
Contreras
,
Ane
Rodrigo-unzueta
,
Natalia
Comino
,
Ana
Carreras-gonzalez
,
Pedro
Arrasate
,
Saioa
Urresti
,
Xevi
Biarnes
,
Antoni
Planas
,
Marcelo
Guerin
Diamond Proposal Number(s):
[8302, 10130]
Abstract: Glycosyltransferases (GTs) play a central role in nature. They catalyze the transfer of a sugar moiety to a broad range of acceptor substrates. GTs are highly selective enzymes, allowing the recognition of subtle structural differences in the sequences and stereochemistry of their sugar and acceptor substrates. We report here a series of structural snapshots of the reaction center of the retaining glucosyl-3-phosphoglycerate synthase (GpgS). During this sequence of events, we visualize how the enzyme guides the substrates into the reaction center where the glycosyl transfer reaction takes place, and unveil the mechanism of product release, involving multiple conformational changes not only in the substrates/products but also in the enzyme. The structural data are further complemented by metadynamics free-energy calculations, revealing how the equilibrium of loop conformations is modulated along these itineraries. The information reported here represent an important contribution for the understanding of GT enzymes at the molecular level.
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Jun 2017
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I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[10130, 8302]
Abstract: ADP-glucose pyrophosphorylase (AGPase) catalyzes the rate-limiting step of bacterial glycogen and plant starch biosynthesis, the most common carbon storage polysaccharides in nature. A major challenge is to understand how AGPase activity is regulated by metabolites in the energetic flux within the cell. Here we report crystal structures of the homotetrameric AGPase from Escherichia coli in complex with its physiological positive and negative allosteric regulators, fructose-1,6-bisphosphate (FBP) and AMP, and sucrose in the active site. FBP and AMP bind to partially overlapping sites located in a deep cleft between glycosyltransferase A-like and left-handed β helix domains of neighboring protomers, accounting for the fact that sensitivity to inhibition by AMP is modulated by the concentration of the activator FBP. We propose a model in which the energy reporters regulate EcAGPase catalytic activity by intra-protomer interactions and inter-protomer crosstalk, with a sensory motif and two regulatory loops playing a prominent role.
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Sep 2016
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[14619]
Open Access
Abstract: The type VI secretion system (T6SS) is a supra-molecular bacterial complex that resembles phage tails. It is a killing machine which fires toxins into target cells upon contraction of its TssBC sheath. Here, we show that TssA1 is a T6SS component forming dode- cameric ring structures whose dimensions match those of the TssBC sheath and which can accommodate the inner Hcp tube. The TssA1 ring complex binds the T6SS sheath and impacts its behaviour in vivo. In the phage, the first disc of the gp18 sheath sits on a baseplate wherein gp6 is a dodecameric ring. We found remarkable sequence and structural similarities between TssA1 and gp6 C-termini, and propose that TssA1 could be a baseplate component of the T6SS. Furthermore, we identified similarities between TssK1 and gp8, the former interacting with TssA1 while the latter is found in the outer radius of the gp6 ring. These obser- vations, combined with similarities between TssF and gp6N- terminus or TssG and gp53, lead us to propose a comparative model between the phage baseplate and the T6SS.
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Aug 2016
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I03-Macromolecular Crystallography
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David
Albesa-jove
,
Zuzana
Svetlíková
,
Montse
Tersa
,
Enea
Sancho-vaello
,
Ana
Carreras-gonzález
,
Pascal
Bonnet
,
Pedro
Arrasate
,
Ander
Eguskiza
,
Shiva K.
Angala
,
Javier Orlando
Cifuente
,
Jana
Korduláková
,
Mary
Jackson
,
Katarína
Mikušová
,
Marcelo
Guerin
Abstract: The biosynthesis of phospholipids and glycolipids are critical pathways for virtually all cell membranes. PatA is an essential membrane associated acyltransferase involved in the biosynthesis of mycobacterial phosphatidyl-myo-inositol mannosides (PIMs). The enzyme transfers a palmitoyl moiety from palmitoyl–CoA to the 6-position of the mannose ring linked to 2-position of inositol in PIM1/PIM2. We report here the crystal structures of PatA from Mycobacterium smegmatis in the presence of its naturally occurring acyl donor palmitate and a nonhydrolyzable palmitoyl–CoA analog. The structures reveal an α/β architecture, with the acyl chain deeply buried into a hydrophobic pocket that runs perpendicular to a long groove where the active site is located. Enzyme catalysis is mediated by an unprecedented charge relay system, which markedly diverges from the canonical HX4D motif. Our studies establish the mechanistic basis of substrate/membrane recognition and catalysis for an important family of acyltransferases, providing exciting possibilities for inhibitor design.
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Mar 2016
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I04-Macromolecular Crystallography
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David
Albesa-jove
,
Natalia
Comino
,
Montse
Tersa
,
Elisabeth
Mohorko
,
Saioa
Urresti
,
Elisa
Dainese
,
Laurent R.
Chiarelli
,
Maria Rosalia
Pasca
,
Riccardo
Manganelli
,
Vadim
Makarov
,
Giovanna
Riccardi
,
Dmitri I.
Svergun
,
Rudi
Glockshuber
,
Marcelo
Guerin
Diamond Proposal Number(s):
[8302, 10130]
Abstract: Rv2466c is a key oxidoreductase that mediates the reductive activation of TP053, a thienopyrimidine derivative that kills replicating and non-replicating Mycobacterium tuberculosis, but whose mode of action remains enigmatic. Rv2466c is a homodimer in which each subunit displays a modular architecture comprising a canonical thioredoxin fold with a Cys19-Pro20-Trp21-Cys22 motif, and an insertion consisting of a four α-helical bundle and a short α-helical hairpin. Strong evidence is provided for dramatic conformational changes during the Rv2466c redox cycle, which are essential for TP053 activity. Strikingly, a new crystal structure of the reduced form of Rv2466c revealed the binding of a C-terminal extension in α-helical conformation to a pocket next to the active site cysteine pair at the interface between the thioredoxin domain and the helical insertion domain. The ab initio low-resolution envelopes obtained from small angle X-ray scattering showed that the fully reduced form of Rv2466c adopts a ′closed′ compact conformation in solution, similar to that observed in the crystal structure. In contrast, the oxidized form of Rv2466c displays an ′open′ conformation, where tertiary structural changes in the α-helical subdomain suffice to account for the observed conformational transitions. Altogether our structural, biochemical and biophysical data strongly support a model in which the formation of the catalytic disulfide bond upon TP053 reduction triggers local structural changes that open the substrate binding site of Rv2466c allowing the release of the activated, reduced form of TP053. Our studies suggest that similar structural changes might have a functional role in other members of the thioredoxin-fold superfamily.
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Nov 2015
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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David
Albesa-jove
,
Fernanda
Mendoza
,
Ane
Rodrigo-unzueta
,
Fernando
Gomollón-bel
,
Javier O.
Cifuente
,
Saioa
Urresti
,
Natalia
Comino
,
Hansel
Gómez
,
Javier
Romero-garcía
,
José M.
Lluch
,
Enea
Sancho-vaello
,
Xevi
Biarnés
,
Antoni
Planas
,
Pedro
Merino
,
Laura
Masgrau
,
Marcelo E.
Guerin
Diamond Proposal Number(s):
[8302, 10130]
Abstract: Glycosyltransferases (GTs) comprise a prominent family of enzymes that play critical roles in a variety of cellular processes, including cell signaling, cell development, and host–pathogen interactions. Glycosyl transfer can proceed with either inversion or retention of the anomeric configuration with respect to the reaction substrates and products. The elucidation of the catalytic mechanism of retaining GTs remains a major challenge. A native ternary complex of a GT in a productive mode for catalysis is reported, that of the retaining glucosyl-3-phosphoglycerate synthase GpgS from M. tuberculosis in the presence of the sugar donor UDP-Glc, the acceptor substrate phosphoglycerate, and the divalent cation cofactor. Through a combination of structural, chemical, enzymatic, molecular dynamics, and quantum-mechanics/molecular-mechanics (QM/MM) calculations, the catalytic mechanism was unraveled, thereby providing a strong experimental support for a front–side substrate-assisted SNi-type reaction.
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Jul 2015
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