I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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George W.
Mobbs
,
Adli A.
Aziz
,
Samuel R.
Dix
,
G. Michael
Blackburn
,
Sveta E.
Sedelnikova
,
Thomas C.
Minshull
,
Mark J.
Dickman
,
Patrick
Baker
,
Sheila
Nathan
,
Mohd Firdaus
Raih
,
David W.
Rice
Diamond Proposal Number(s):
[8987, 17773]
Open Access
Abstract: Burkholderia pseudomallei lethal factor 1 (BLF1) exhibits site-specific glutamine deamidase activity against the eukaryotic RNA helicase, eIF4A, thereby blocking mammalian protein synthesis. The structure of a complex between BLF1 C94S and human eIF4A shows that the toxin binds in the cleft between the two RecA-like eIF4A domains forming interactions with residues from both and with the scissile amide of the target glutamine, Gln339, adjacent to the toxin active site. The RecA-like domains adopt a radically twisted orientation compared to other eIF4A structures and the nature and position of conserved residues suggests this may represent a conformation associated with RNA binding. Comparison of the catalytic site of BLF1 with other deamidases and cysteine proteases reveals that they fall into two classes, related by pseudosymmetry, that present either the re or si faces of the target amide/peptide to the nucleophilic sulfur, highlighting constraints in the convergent evolution of their Cys-His active sites.
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Mar 2022
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I02-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Nur Zazarina
Ramly
,
Samuel R.
Dix
,
Sergey N.
Ruzheinikov
,
Svetlana E.
Sedelnikova
,
Patrick J.
Baker
,
Yock-Ping
Chow
,
Fiona M.
Tomley
,
Damer P.
Blake
,
Kiew-Lian
Wan
,
Sheila
Nathan
,
David W.
Rice
Diamond Proposal Number(s):
[1218, 24447]
Open Access
Abstract: In infections by apicomplexan parasites including Plasmodium, Toxoplasma gondii, and Eimeria, host interactions are mediated by proteins including families of membrane-anchored cysteine-rich surface antigens (SAGs) and SAG-related sequences (SRS). Eimeria tenella causes caecal coccidiosis in chickens and has a SAG family with over 80 members making up 1% of the proteome. We have solved the structure of a representative E. tenella SAG, EtSAG19, revealing that, despite a low level of sequence similarity, the entire Eimeria SAG family is unified by its three-layer αβα fold which is related to that of the CAP superfamily. Furthermore, sequence comparisons show that the Eimeria SAG fold is conserved in surface antigens of the human coccidial parasite Cyclospora cayetanensis but this fold is unrelated to that of the SAGs/SRS proteins expressed in other apicomplexans including Plasmodium species and the cyst-forming coccidia Toxoplasma gondii, Neospora caninum and Besnoitia besnoiti. However, despite having very different structures, Consurf analysis showed that Eimeria SAG and Toxoplasma SRS families each exhibit marked hotspots of sequence hypervariability that map to their surfaces distal to the membrane anchor. This suggests that the primary and convergent purpose of the different structures is to provide a platform onto which sequence variability can be imposed.
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Mar 2021
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I03-Macromolecular Crystallography
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Open Access
Abstract: Enzyme regulation is vital for metabolic adaptability in living systems. Fine control of enzyme activity is often delivered through post-translational mechanisms, such as allostery or allokairy. β-phosphoglucomutase (βPGM) from Lactococcus lactis is a phosphoryl transfer enzyme required for complete catabolism of trehalose and maltose, through the isomerisation of β-glucose 1-phosphate to glucose 6-phosphate via β-glucose 1,6-bisphosphate. Surprisingly for a gatekeeper of glycolysis, no fine control mechanism of βPGM has yet been reported. Herein, we describe allomorphy, a post-translational control mechanism of enzyme activity. In βPGM, isomerisation of the K145-P146 peptide bond results in the population of two conformers that have different activities owing to repositioning of the K145 sidechain. In vivo phosphorylating agents, such as fructose 1,6-bisphosphate, generate phosphorylated forms of both conformers, leading to a lag phase in activity until the more active phosphorylated conformer dominates. In contrast, the reaction intermediate β-glucose 1,6-bisphosphate, whose concentration depends on the β-glucose 1-phosphate concentration, couples the conformational switch and the phosphorylation step, resulting in the rapid generation of the more active phosphorylated conformer. In enabling different behaviours for different allomorphic activators, allomorphy allows an organism to maximise its responsiveness to environmental changes while minimising the diversion of valuable metabolites.
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Nov 2020
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Shiqi
Ji
,
Samuel R.
Dix
,
Adli A.
Aziz
,
Svetlana E.
Sedelnikova
,
Patrick J.
Baker
,
John B.
Rafferty
,
Per A.
Bullough
,
Svetomir B.
Tzokov
,
Jon
Agirre
,
Fu-Li
Li
,
David W.
Rice
Diamond Proposal Number(s):
[17773]
Open Access
Abstract: Alginate is a polymer containing two uronic acid epimers, β-d-mannuronate (M) and α-l-guluronate (G), and is a major component of brown seaweed that is depolymerized by alginate lyases. These enzymes have diverse specificity, cleaving the chain with endo- or exotype activity and with differential selectivity for the sequence of M or G at the cleavage site. Dp0100 is a 201-kDa multi-modular, broad-specificity endotype alginate lyase from the marine thermophile Defluviitalea phaphyphila, which uses brown algae as a carbon source, converting it to ethanol, and bioinformatics analysis suggested that its catalytic domain represents a new polysaccharide lyase family, PLxx. The structure of the Dp0100 catalytic domain, determined at 2.07 Å resolution, revealed that it comprises three regions strongly resembling those of the exotype lyase families PL15 and PL17. The conservation of key catalytic histidine and tyrosine residues belonging to the latter suggest these enzymes share mechanistic similarities. A complex of Dp0100 with a pentasaccharide, M5, showed that the oligosaccharide is located in subsites –2, –1, +1, +2, and +3 in a long, deep canyon open at both ends, explaining the endotype activity of this lyase. This contrasted with the hindered binding sites of the exotype enzymes, which are blocked such that only one sugar moiety can be accommodated at the –1 position in the catalytic site. The biochemical and structural analyses of Dp0100, the first for this new class of endotype alginate lyases, has furthered our understanding of the structure-function and evolutionary relationships within this important class of enzymes.
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Oct 2019
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I02-Macromolecular Crystallography
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Diamond Proposal Number(s):
[12788]
Open Access
Abstract: C4-dicarboxylates play a central role in cellular physiology as key metabolic intermediates. Under aerobic conditions, they participate in the citric-acid cycle, while in anaerobic bacteria, they are important in energy-conserving fermentation and respiration processes. Ten different families of secondary transporters have been described to participate in C4-dicarboxylate movement across biological membranes but only one of these utilizes an extracytoplasmic solute binding protein to achieve high-affinity uptake. Here, we identify the MatBAC system from the photosynthetic bacterium Rhodopseudomonas palustris as the first member of the Tripartite Tricarboxylate Transport (TTT) family to be involved in C4-dicarboxylate transport. Tryptophan fluorescence spectroscopy showed that MatC, the periplasmic binding protein from this system, binds to L- and D-malate with Kd values of 27 and 21 nM respectively, the highest reported affinity to date for these C4-dicarboxylates, and to succinate (Kd 110 nM) and fumarate (Kd 400 nM). The 2.1 Å crystal structure of MatC with bound malate shows a high level of substrate coordination, with participation of two water molecules that bridge hydrogen bonds between the ligand proximal carboxylic group and the main chain of two conserved loops in the protein structure. The substrate coordination in MatC correlates with the binding data, and explains the protein's selectivity for different substrates and respective binding affinities. Our results reveal a new function in C4-dicarboxylate transport by members of the poorly characterized TTT family, which are widely distributed in bacterial genomes but for which details of structure–function relationships and transport mechanisms have been lacking.
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Nov 2018
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Samuel R.
Dix
,
Hayley J.
Owen
,
Ruyue
Sun
,
Asma
Ahmad
,
Sravanthi
Shastri
,
Helena L.
Spiewak
,
Daniel J.
Mosby
,
Matthew J.
Harris
,
Sarah L.
Batters
,
Thomas A.
Brooker
,
Svetomir B.
Tzokov
,
Svetlana E.
Sedelnikova
,
Patrick J.
Baker
,
Per A.
Bullough
,
David W.
Rice
,
Mark S.
Thomas
Diamond Proposal Number(s):
[8987, 12788, 17773]
Open Access
Abstract: The type VI secretion system (T6SS) is a multi-protein complex that injects bacterial effector proteins into target cells. It is composed of a cell membrane complex anchored to a contractile bacteriophage tail-like apparatus consisting of a sharpened tube that is ejected by the contraction of a sheath against a baseplate. We present structural and biochemical studies on TssA subunits from two different T6SSs that reveal radically different quaternary structures in comparison to the dodecameric E. coli TssA that arise from differences in their C-terminal sequences. Despite this, the different TssAs retain equivalent interactions with other components of the complex and position their highly conserved N-terminal ImpA_N domain at the same radius from the centre of the sheath as a result of their distinct domain architectures, which includes additional spacer domains and highly mobile interdomain linkers. Together, these variations allow these distinct TssAs to perform a similar function in the complex.
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Nov 2018
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I02-Macromolecular Crystallography
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Abstract: Ubiquitin specific proteases (USPs) reverse ubiquitination and regulate virtually all cellular processes. Defined non-catalytic domains in USP4 and USP15 are known to interact with E3 ligases and substrate recruitment factors. No such interactions have been reported for these domains in the paralog USP11, a key regulator of DNA double-strand break repair by homologous recombination (HR). We hypothesized that USP11 domains adjacent to its protease domain harbour unique peptide-binding sites. Here, using a next-generation phage display (NGPD) strategy, combining phage display library screening with next generation sequencing, we discovered unique USP11 interacting peptide motifs. Isothermal titration calorimetry disclosed that the highest affinity peptides (KD of ~10 μM) exhibit exclusive selectivity for USP11 over USP4 and USP15 in vitro. Furthermore, a crystal structure of a USP11-peptide complex revealed a previously unknown binding site in USP11’s non-catalytic ubiquitin-like (UBL) region. This site interacted with a helical motif and is absent in USP4 and USP15. Reporter assays using USP11-WT versus a binding pocket-deficient double mutant disclosed that this binding site modulates USP11’s function in HR-mediated DNA repair. The highest affinity USP11 peptide binder fused to a cellular delivery sequence induced significant nuclear localization and cell cycle arrest in S phase, affecting the viability of different mammalian cell lines. The USP11 peptide ligands and the paralog-specific functional site in USP11 identified here provide a framework for the development of new biochemical tools and therapeutic agents. We propose that an NGPD-based strategy for identifying interacting peptides may be applied also to other cellular targets.
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Oct 2018
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Open Access
Abstract: TssA is a core subunit of the type VI secretion system, which is a major player in interspecies competition in Gram-negative bacteria. Previous studies on enteroaggregative Escherichia coli TssA suggested that it is comprised of three putative domains: a conserved N-terminal domain, a middle domain and a ring-forming C-terminal domain. X-ray studies of the latter two domains have identified their respective structures. Here, the results of the expression and purification of full-length and domain constructs of TssA from Aeromonas hydrophila are reported, resulting in diffraction-quality crystals for the middle domain (Nt2) and a construct including the middle and C-terminal domains (Nt2-CTD).
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Sep 2018
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[12788]
Abstract: The Tripartite Tricarboxylate Transporter (TTT) family is a poorly characterised group of prokaryotic secondary solute transport systems, which employ a periplasmic substrate binding-protein (SBP) for initial ligand recognition. The substrates of only a small number of TTT systems are known and very few SBP structures have been solved, so the mechanisms of SBP-ligand interactions in this family are not well understood. The SBP RPA4515 (AdpC) from Rhodopseudomonas palustris was found by differential scanning fluorescence and isothermal titration calorimetry to bind aliphatic dicarboxylates of a chain length of six to nine carbons, with KD values in the μM range. The highest affinity was found for the C6-dicarboxylate adipate (1,6-hexanedioate). Crystal structures of AdpC with either adipate or 2-oxoadipate bound revealed a lack of positively charged amino-acids in the binding pocket and showed that water molecules are involved in bridging hydrogen bonds to the substrate, a conserved feature in the TTT SBP family that is distinct from other types of SBP. In AdpC, both of the ligand carboxylate groups and a linear chain conformation are needed for coordination in the binding pocket. RT-PCR showed that adpC expression is upregulated by low environmental adipate concentrations, suggesting adipate is a physiologically relevant substrate but as adpC is not genetically linked to any TTT membrane transport genes, the role of AdpC may be in signalling rather than transport. Our data expands the known ligands for TTT systems and identifies a novel high-affinity binding-protein for adipate, an important industrial chemical intermediate and food additive.
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Oct 2017
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