I04-1-Macromolecular Crystallography (fixed wavelength)
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Marcin
Bielecki
,
Svetlana
Antonyuk
,
Richard W.
Strange
,
Klaudia
Siemińska
,
John W.
Smalley
,
Paweł
Mackiewicz
,
Michał
Śmiga
,
Megan
Cowan
,
Michael J.
Capper
,
Paulina
Ślęzak
,
Mariusz
Olczak
,
Teresa
Olczak
Diamond Proposal Number(s):
[15991]
Open Access
Abstract: As part of the infective process, Porphyromonas gingivalis must acquire heme which is indispensable for life and enables the microorganism to survive and multiply at the infection site. This oral pathogenic bacterium uses a newly discovered novel hmu heme uptake system with a leading role played by the HmuY hemophore-like protein, responsible for acquiring heme and increasing virulence of this periodontopathogen. We demonstrated that Prevotella intermedia produces two HmuY homologs, termed PinO and PinA. Both proteins were produced at higher mRNA and protein levels when the bacterium grew under low-iron/heme conditions. PinO and PinA bound heme, but preferentially under reducing conditions, and in a manner different to that of the P. gingivalis HmuY. The analysis of the three-dimensional structures confirmed differences between apo-PinO and apo-HmuY, mainly in the fold forming the heme-binding pocket. Instead of two histidine residues coordinating heme iron in P. gingivalis HmuY, PinO and PinA could use one methionine residue to fulfil this function, with potential support of additional methionine residue/s. The P. intermedia proteins sequestered heme only from the host albumin-heme complex under reducing conditions. Our findings suggest that HmuY-like family might comprise proteins subjected during evolution to significant diversification, resulting in different heme coordination mode. The newer data presented in this manuscript on HmuY homologs produced by P. intermedia sheds more light on the novel mechanism of heme uptake, could be helpful in discovering their biological function, and in developing novel therapeutic approaches.
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Jan 2020
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I03-Macromolecular Crystallography
I23-Long wavelength MX
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[12579]
Open Access
Abstract: Under limiting sulfur availability, bacteria can assimilate sulfur from alkanesulfonates. Bacteria utilize ATP-binding cassette (ABC) transporters to internalise them for further processing to release sulfur. In gram-negative bacteria the TauABC and SsuABC ensure internalization, although, these two systems have common substrates, the former has been characterized as a taurine specific system. TauA and SsuA are substrate-binding proteins (SBPs) that bind and bring the alkanesulfonates to the ABC importer for transport. Here, we have determined the crystal structure of TauA and have characterized its thermodynamic binding parameters by isothermal titration calorimetry in complex with taurine and different alkanesulfonates. Our structures revealed that the coordination of the alkanesulfonates is conserved, with the exception of Asp205 that is absent from SsuA, but the thermodynamic parameters revealed a very high enthalpic penalty cost for binding of the other alkanesulfonates relative to taurine. Our molecular dynamic simulations indicated that the different levels of hydration of the binding site contributed to the selectivity for taurine over the other alkanesulfonates. Such selectivity mechanism is very likely to be employed by other SBPs of ABC transporters.
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Nov 2019
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Eidarus
Salah
,
Deep
Chatterjee
,
Alessandra
Beltrami
,
Anthony
Tumber
,
Franziska
Preuss
,
Peter
Canning
,
Apirat
Chaikuad
,
Petra
Knaus
,
Stefan
Knapp
,
Alex N.
Bullock
,
Sebastian
Mathea
Diamond Proposal Number(s):
[6391, 10619]
Abstract: LIM domain kinase 1 (LIMK1) is a key regulator of actin dynamics. It is thereby a potential therapeutic target for the prevention of fragile X syndrome and amyotrophic lateral sclerosis. Herein, we use X-ray crystallography and activity assays to describe how LIMK1 accomplishes substrate specificity, to suggest a unique 'rock-and-poke' mechanism of catalysis and to explore the regulation of the kinase by activation loop phosphorylation. Based on these findings, a differential scanning fluorimetry assay and a RapidFire mass spectrometry activity assay were established, leading to the discovery and confirmation of a set of small-molecule LIMK1 inhibitors. Interestingly, several of the inhibitors were inactive towards the closely related isoform LIMK2. Finally, crystal structures of the LIMK1 kinase domain in complex with inhibitors (PF-477736 and staurosporine, respectively) are presented, providing insights into LIMK1 plasticity upon inhibitor binding.
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Oct 2019
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B23-Circular Dichroism
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Diamond Proposal Number(s):
[15094, 17698, 19120]
Open Access
Abstract: The light reactions of photosynthesis are hosted and regulated by the chloroplast thylakoid membrane (TM) — the central structural component of the photosynthetic apparatus of plants and algae. The two-dimensional and three-dimensional arrangement of the lipid–protein assemblies, aka macroorganisation, and its dynamic responses to the fluctuating physiological environment, aka flexibility, are the subject of this review. An emphasis is given on the information obtainable by spectroscopic approaches, especially circular dichroism (CD). We briefly summarise the current knowledge of the composition and three-dimensional architecture of the granal TMs in plants and the supramolecular organisation of Photosystem II and light-harvesting complex II therein. We next acquaint the non-specialist reader with the fundamentals of CD spectroscopy, recent advances such as anisotropic CD, and applications for studying the structure and macroorganisation of photosynthetic complexes and membranes. Special attention is given to the structural and functional flexibility of light-harvesting complex II in vitro as revealed by CD and fluorescence spectroscopy. We give an account of the dynamic changes in membrane macroorganisation associated with the light-adaptation of the photosynthetic apparatus and the regulation of the excitation energy flow by state transitions and non-photochemical quenching.
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Oct 2019
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[12342]
Open Access
Abstract: Human zinc-α2-glycoprotein (ZAG) is a 42 kDa adipokine which regulates body fat mass and is associated with cachexia and obesity. ZAG belongs to the major histocompatibility complex class I protein family and binds long chain polyunsaturated fatty acids in its groove formed from the α1 and α2 domains. To identify the molecular basis of its lipid-binding function, we determined the first crystal structure at 2.49Å resolution for fatty acid-bound ZAG, where the ligand was the fluorescent 11-(dansylamino)undecanoic acid (DAUDA). The 192 kDa crystallographic asymmetric unit contained six ZAG and eight fatty acid molecules in unique conformations. Six fatty acid molecules were localised to the ZAG grooves, where its tails were bound in two distinct conformations. The carboxylate groups of three fatty acids projected out of the groove, while the fourth was hydrogen bonded with R73 inside the groove. Other ligand-residue contacts were primarily hydrophobic. A new fatty acid site was revealed for two further DAUDA molecules at the ZAG α3 domains. Following conformational changes from unbound ZAG, the α3 domains formed tetrameric β-barrel structures lined by fatty acid molecules that doubled the binding capacity of ZAG. Analytical ultracentrifugation revealed that ZAG in solution was a monomer in the absence of DAUDA, but formed small amounts of tetramers with DAUDA. By showing that ZAG binds fatty acids in different locations, we demonstrate an augmented mechanism for fatty acid binding in ZAG that is distinct from other known fatty acid binding proteins, and may be relevant to cachexia.
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Sep 2019
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B21-High Throughput SAXS
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Diamond Proposal Number(s):
[14794]
Open Access
Abstract: The trifunctional enzyme (TFE) catalyzes the last three steps of the fatty acid β-oxidation cycle. Two TFEs are present in Escherichia coli , EcTFE and anEcTFE. EcTFE is expressed only under aerobic conditions whereas anEcTFE is expressed also under anaerobic conditions, with nitrate or fumarate as the ultimate electron acceptor. The anEcTFE subunits have higher sequence identity with the human mitochondrial TFE (HsTFE) than with the soluble EcTFE. Like HsTFE, here it is found that anEcTFE is a membrane bound complex. Systematic enzyme kinetic studies show that anEcTFE has preference for medium and long chain enoyl-CoAs, similar to HsTFE, whereas EcTFE prefers short chain enoyl-CoA substrates. The biophysical characterization of anEcTFE and EcTFE shows that EcTFE is heterotetrameric, whereas anEcTFE is purified as a complex of two heterotetrameric units, like HsTFE. The tetrameric assembly of anEcTFE resembles the HsTFE tetramer, although the arrangement of the two anEcTFE tetramers in the octamer is different from the HsTFE octamer. These studies demonstrate that EcTFE and anEcTFE have complementary substrate specificities, allowing for complete degradation of long chain enoyl-CoAs under aerobic conditions. The new data agree with the notion that anEcTFE and HsTFE are evolutionary closely related, whereas EcTFE belongs to a separate subfamily.
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Jun 2019
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I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[17212]
Open Access
Abstract: Angiotensin-converting enzyme (ACE) is a zinc metalloprotease best known for its role in blood pressure regulation. ACE consists of two homologous catalytic domains, the N- and C-domain, that display distinct but overlapping catalytic functions in vivo owing to subtle differences in substrate specificity. While current generation ACE inhibitors target both ACE domains, domain-selective ACE inhibitors may be clinically advantageous, either reducing side-effects or having utility in new indications. Here, we used site-directed mutagenesis, an ACE chimera and X-ray crystallography to unveil the molecular basis for C-domain selective ACE inhibition by the bradykinin potentiating peptide b (BPPb), naturally present in Brazilian pit viper venom. We present the BPPb-N-domain structure in comparison with the previously reported BPPb-C-domain structure and highlight key differences in peptide interactions with the S4 to S9 subsites. This suggests involvement of these subsites in conferring C-domain selective BPPb binding, in agreement with the mutagenesis results where unique residues governing differences in active site exposure, lid structure and dynamics between the two domains were the major drivers for C-domain selective BPPb binding. Mere disruption of BPPb interactions with unique S2 and S4 subsite residues, which synergistically assist in BPPb binding, was insufficient to abolish C-domain selectivity. The combination of unique S9-S4 and S2ʹ subsite C-domain residues were required for the favourable entry, orientation and thus, selective binding of the peptide. This emphasizes the need to consider factors other than direct protein-inhibitor interactions to guide the design of domain-selective ACE inhibitors, especially in the case of larger peptides.
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May 2019
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B21-High Throughput SAXS
I03-Macromolecular Crystallography
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Open Access
Abstract: The group A p21-activated kinases (PAKs) exist in an auto-inhibited form until activated by GTPase binding and auto-phosphorylation. In the auto-inhibited form a regulatory domain binds to the kinase domain blocking the binding of substrates, and CDC42 or Rac binding to the regulatory domain relieves this auto-inhibition allowing auto-phosphorylation on the kinase domain activation loop. We have determined the crystal structure of the PAK3 catalytic domain and by small angle X-ray scattering the solution-phase structures of full-length inactive PAK1 and PAK3. The structures reveal a compact but elongated molecular shape that demonstrates that, together with multiple independent biophysical measurements and in contrast to previous assumptions, group A PAKs are monomeric both before and after activation, consistent with an activation mechanism of cis -autoinhibition and initial cis -autophosphorylation, followed by transient dimerization to allow trans- autophosphorylation for full activation, yielding a monomeric active PAK protein.
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Apr 2019
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I04-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[9487]
Open Access
Abstract: Ferritins are a large family of intracellular proteins that protect the cell from oxidative stress by catalytically converting Fe(II) into less toxic Fe(III) and storing iron minerals within their core. Encapsulated ferritins (EncFtn) are a sub-family of ferritin-like proteins, which are widely distributed in all bacterial and archaeal phyla. The recently characterized Rhodospirillum rubrum EncFtn displays an unusual structure when compared with classical ferritins, with an open decameric structure that is enzymatically active, but unable to store iron. This EncFtn must be associated with an encapsulin nanocage in order to act as an iron store. Given the wide distribution of the EncFtn family in organisms with diverse environmental niches, a question arises as to whether this unusual structure is conserved across the family. Here, we characterize EncFtn proteins from the halophile Haliangium ochraceum and the thermophile Pyrococcus furiosus, which show the conserved annular pentamer of dimers topology. Key structural differences are apparent between the homologues, particularly in the centre of the ring and the secondary metal-binding site, which is not conserved across the homologues. Solution and native mass spectrometry analyses highlight that the stability of the protein quaternary structure differs between EncFtn proteins from different species. The ferroxidase activity of EncFtn proteins was confirmed, and we show that while the quaternary structure around the ferroxidase centre is distinct from classical ferritins, the ferroxidase activity is still inhibited by Zn(II). Our results highlight the common structural organization and activity of EncFtn proteins, despite diverse host environments and contexts within encapsulins.
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Mar 2019
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I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
I04-Macromolecular Crystallography
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Open Access
Abstract: The SCP2-thiolase (type-1) functions in the vertebrate peroxisomal, bile acid synthesis pathway, converting 24-keto-THC-CoA and CoA into choloyl-CoA and propionyl-CoA. This conversion concerns the β-oxidation chain shortening of the steroid fatty acyl moiety of 24-keto-THC-CoA. This class of dimeric thiolases has previously been poorly characterized. High resolution crystal structures of the zebrafish SCP2-thiolase (type-1) now reveal an open catalytic site, shaped by residues of both subunits. The structure of its non-dimerised monomeric form has also been captured in the obtained crystals. Four loops at the dimer interface adopt very different conformations in the monomeric form. These loops also shape the active site and their structural changes explain why a competent active site is not present in the monomeric form. Native mass spectrometry studies confirm that the zebrafish SCP2-thiolase (type-1) as well as its human homologue are weak transient dimers in solution. The crystallographic binding studies reveal the mode of binding of CoA and octanoyl-CoA in the active site, highlighting the conserved geometry of the nucleophilic cysteine, the catalytic acid/base cysteine and the two oxyanion holes. The dimer interface of SCP2-thiolase (type-1) is equally extensive as in other thiolase dimers, however it is more polar than any of the corresponding interfaces, which correlates with the notion that the enzyme forms a weak transient dimer. The structure comparison of the monomeric and dimeric forms suggests functional relevance of this property. These comparisons provide also insight into the structural rearrangements that occur when the folded inactive monomers assemble into the mature dimer.
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Dec 2018
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