I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
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Diamond Proposal Number(s):
[19951, 24732]
Open Access
Abstract: The Mycobacterium tuberculosis trifunctional enzyme (MtTFE) is an α2β2 tetrameric enzyme in which the α-chain harbors the 2E-enoyl-CoA hydratase (ECH) and 3S-hydroxyacyl-CoA dehydrogenase (HAD) active sites, and the β-chain provides the 3-ketoacyl-CoA thiolase (KAT) active site. Linear, medium-chain and long-chain 2E-enoyl-CoA molecules are the preferred substrates of MtTFE. Previous crystallographic binding and modeling studies identified binding sites for the acyl-CoA substrates at the three active sites, as well as the NAD binding pocket at the HAD active site. These studies also identified three additional CoA binding sites on the surface of MtTFE that are different from the active sites. It has been proposed that one of these additional sites could be of functional relevance for the substrate channeling (by surface crawling) of reaction intermediates between the three active sites. Here, 226 fragments were screened in a crystallographic fragment-binding study of MtTFE crystals, resulting in the structures of 16 MtTFE–fragment complexes. Analysis of the 121 fragment-binding events shows that the ECH active site is the `binding hotspot' for the tested fragments, with 41 binding events. The mode of binding of the fragments bound at the active sites provides additional insight into how the long-chain acyl moiety of the substrates can be accommodated at their proposed binding pockets. In addition, the 20 fragment-binding events between the active sites identify potential transient binding sites of reaction intermediates relevant to the possible channeling of substrates between these active sites. These results provide a basis for further studies to understand the functional relevance of the latter binding sites and to identify substrates for which channeling is crucial.
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Aug 2024
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I24-Microfocus Macromolecular Crystallography
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Open Access
Abstract: The Fe2+-dependent E. coli enzyme FucO catalyzes the reversible interconversion of short-chain (S)-lactaldehyde and (S)-1,2-propanediol, using NADH and NAD+ as cofactors, respectively. Laboratory-directed evolution experiments have been carried out previously using phenylacetaldehyde as the substrate for screening catalytic activity with bulky substrates, which are very poorly reduced by wild-type FucO. These experiments identified the N151G/L259V double mutant (dubbed DA1472) as the most active variant with this substrate via a two-step evolutionary pathway, in which each step consisted of one point mutation. Here the crystal structures of DA1472 and its parent D93 (L259V) are reported, showing that these amino acid substitutions provide more space in the active site, though they do not cause changes in the main-chain conformation. The catalytic activity of DA1472 with the physiological substrate (S)-lactaldehyde and a series of substituted phenylacetaldehyde derivatives were systematically quantified and compared with that of wild-type as well as with the corresponding point-mutation variants (N151G and L259V). There is a 9000-fold increase in activity, when expressed as kcat/KM values, for DA1472 compared with wild-type FucO for the phenylacetaldehyde substrate. The crystal structure of DA1472 complexed with a non-reactive analog of this substrate (3,4-dimethoxyphenylacetamide) suggests the mode of binding of the bulky group of the new substrate. These combined structure–function studies therefore explain the dramatic increase in catalytic activity of the DA1472 variant for bulky aldehyde substrates. The structure comparisons also suggest why the active site in which Fe2+ is replaced by Zn2+ is not able to support catalysis.
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Jul 2023
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I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[14794]
Open Access
Abstract: Four catalytic amino acids at triosephosphate isomerase (TIM) are highly conserved: N11, K13, H95, and E167. Asparagine 11 is the last of these to be characterized in mutagenesis studies. The ND2 side chain atom of N11 is hydrogen bonded to the O-1 hydroxyl of enzyme-bound dihydroxyacetone phosphate (DHAP), and it sits in an extended chain of hydrogen-bonded side chains that includes T75′ from the second subunit. The N11A variants of wild-type TIM from Trypanosoma brucei brucei (TbbTIM) and Leishmania mexicana (LmTIM) undergo dissociation from the dimer to monomer under our assay conditions. Values of Kas = 8 × 103 and 1 × 106 M–1, respectively, were determined for the conversion of monomeric N11A TbbTIM and LmTIM into their homodimers. The N11A substitution at the variant of LmTIM previously stabilized by the E65Q substitution gives the N11A/E65Q variant that is stable to dissociation under our assay conditions. The X-ray crystal structure of N11A/E65Q LmTIM shows an active site that is essentially superimposable on that for wild-type TbbTIM, which also has a glutamine at position 65. A comparison of the kinetic parameters for E65Q LmTIM and N11A/E65Q LmTIM-catalyzed reactions of (R)-glyceraldehyde 3-phosphate (GAP) and (DHAP) shows that the N11A substitution results in a (13–14)-fold decrease in kcat/Km for substrate isomerization and a similar decrease in kcat for DHAP but only a 2-fold decrease in kcat for GAP.
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May 2023
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I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[19951]
Open Access
Abstract: Facultative anaerobic bacteria such as Escherichia coli have two α2β2 heterotetrameric trifunctional enzymes (TFE), catalyzing the last three steps of the β-oxidation cycle: soluble aerobic TFE (EcTFE) and membrane-associated anaerobic TFE (anEcTFE), closely related to the human mitochondrial TFE (HsTFE). The cryo-EM structure of anEcTFE and crystal structures of anEcTFE-α show that the overall assembly of anEcTFE and HsTFE is similar. However, their membrane-binding properties differ considerably. The shorter A5-H7 and H8 regions of anEcTFE-α result in weaker α-β as well as α-membrane interactions, respectively. The protruding H-H region of anEcTFE-β is therefore more critical for membrane-association. Mutational studies also show that this region is important for the stability of the anEcTFE-β dimer and anEcTFE heterotetramer. The fatty acyl tail binding tunnel of the anEcTFE-α hydratase domain, as in HsTFE-α, is wider than in EcTFE-α, accommodating longer fatty acyl tails, in good agreement with their respective substrate specificities.
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May 2023
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I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[23346]
Open Access
Abstract: Mitochondrial fatty acid synthesis (mtFAS) is essential for respiratory function. MtFAS generates the octanoic acid precursor for lipoic acid synthesis, but the role of longer fatty acid products has remained unclear. The structurally well-characterized component of mtFAS, human 2E-enoyl-ACP reductase (MECR) rescues respiratory growth and lipoylation defects of a Saccharomyces cerevisiae Δetr1 strain lacking native mtFAS enoyl reductase. To address the role of longer products of mtFAS, we employed in silico molecular simulations to design a MECR variant with a shortened substrate binding cavity. Our in vitro and in vivo analyses indicate that the MECR G165Q variant allows synthesis of octanoyl groups but not long chain fatty acids, confirming the validity of our computational approach to engineer substrate length specificity. Furthermore, our data imply that restoring lipoylation in mtFAS deficient yeast strains is not sufficient to support respiration and that long chain acyl-ACPs generated by mtFAS are required for mitochondrial function.
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Feb 2023
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I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
VMXi-Versatile Macromolecular Crystallography in situ
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Abhinandan V.
Murthy
,
Ramita
Sulu
,
Andrey
Lebedev
,
Antti M.
Salo
,
Kati
Korhonen
,
Rajaram
Venkatesan
,
Hongmin
Tu
,
Ulrich
Bergmann
,
Janne
Jänis
,
Mikko
Laitaoja
,
Lloyd
Ruddock
,
Johanna
Myllyharju
,
M. Kristian
Koski
,
Rik. K.
Wierenga
Diamond Proposal Number(s):
[20001, 13172, 19951]
Open Access
Abstract: Collagen prolyl 4-hydroxylases (C-P4H) are α2β2 tetramers, which catalyze the prolyl 4-hydroxylation of procollagen chains, allowing for the formation of the stable triple-helical collagen structure in the endoplasmic reticulum. The C-P4H α-subunit provides the N-terminal dimerization domain, the middle peptide-substrate-binding domain (PSB), and the C-terminal catalytic (CAT) domain, while the β-subunit is identical to the enzyme protein disulfide isomerase (PDI). The structure of the N-terminal part of the α-subunit (N-terminal and PSB domain) is known, but the structures of the PSB-CAT linker region and the CAT domain as well as its mode of assembly with the β/PDI-subunit, are not known. Here we report the crystal structure of the CAT domain of human C-P4H-II complexed with the intact β/PDI-subunit, at 3.8Å resolution. The CAT domain interacts with the a, b’, and a’ domains of the β/PDI-subunit, such that the CAT active site is facing bulk solvent. The structure also shows that the C-P4H-II CAT domain has a unique N-terminal extension, consisting of α-helices and a β-strand, which is the edge strand of its major antiparallel β-sheet. This extra region of the CAT domain interacts tightly with the β/PDI-subunit, showing that the CAT-PDI interface includes an inter-subunit disulfide bridge with the a’ domain and tight hydrophobic interactions with the b’ domain. Using this new structural information, the structure of the mature C-P4H-II α2β2 tetramer is predicted. The model suggests that the CAT active site properties are modulated by α-helices of the N-terminal dimerization domains of both subunits of the α2-dimer.
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Oct 2022
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I03-Macromolecular Crystallography
I24-Microfocus Macromolecular Crystallography
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Diamond Proposal Number(s):
[24732, 19951]
Open Access
Abstract: A group-III iron containing 1,2-propanediol oxidoreductase, FucO, (also known as lactaldehyde reductase) from Escherichia coli was examined regarding its structure-dynamics-function relationships in the catalysis of the NADH dependent reduction of (2S)-lactaldehyde. Crystal structures of FucO variants in the presence or absence of cofactors have been determined, illustrating large domain movements between the apo and holo enzyme structures. Different structures of FucO variants co-crystallized with NAD+ or NADH together with substrate further suggest dynamic properties of the nicotinamide moiety of the coenzyme that are important for the reaction mechanism. Modeling of the native substrate (2S)-lactaldehyde into the active site can explain the stereoselectivity exhibited by the enzyme, with a critical hydrogen bond interaction between the (2S)-hydroxyl and the side-chain of N151, as well as the previously experimentally demonstrated pro-(R) selectivity in hydride transfer from NADH to the aldehydic carbon. Furthermore, the deuterium kinetic isotope effect of hydride transfer suggests that reduction chemistry is the main rate limiting step for turnover which is not the case in FucO catalyzed alcohol oxidation. We further propose that a water molecule in the active site – hydrogen bonded to a conserved histidine (H267) and the 2’-hydroxyl of the coenzyme ribose – functions as a catalytic proton donor in the protonation of the product alcohol. A hydrogen bond network of water molecules and the side chains of amino acid residues D360 and H267 links bulk solvent to this proposed catalytic water molecule.
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Aug 2022
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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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Diamond Proposal Number(s):
[19951, 26302, 14794, 10291]
Open Access
Abstract: The Mycobacterium tuberculosis trifunctional enzyme (MtTFE) is an α2β2 tetrameric enzyme. The α-chain harbors the 2E-enoyl-CoA hydratase (ECH) and 3S-hydroxyacyl-CoA dehydrogenase (HAD) activities and the β-chain provides the 3-ketoacyl-CoA thiolase (KAT) activity. Enzyme kinetic data reported here show that medium and long chain enoyl-CoA molecules are preferred substrates for MtTFE. Modelling studies indicate how the linear medium and long acyl chains of these substrates can bind to each of the active sites. In addition, crystallographic binding studies have identified three new CoA binding sites which are different from the previously known CoA binding sites of the three TFE active sites. Structure comparisons provide new insights into the properties of ECH, HAD and KAT active sites of MtTFE. The interactions of the adenine moiety of CoA with loop-2 of the ECH active site cause a conformational change of this loop by which a competent ECH active site is formed. The NAD+ binding domain (domain C) of the HAD part of MtTFE has only a few interactions with the rest of the complex and adopts a range of open conformations, whereas the A-domain of the ECH part is rigidly fixed with respect to the HAD part. Two loops, the CB1-CA1 region and the catalytic CB4-CB5 loop, near the thiolase active site and the thiolase dimer interface, have high B-factors. Structure comparisons suggest that a competent and stable thiolase dimer is formed only when complexed with the α-chains, highlighting the importance of the assembly for the proper functioning of the complex.
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Sep 2021
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Ed
Daniel
,
Mirko M.
Maksimainen
,
Neil
Smith
,
Ville
Ratas
,
Ekaterina
Biterova
,
Sudarshan N.
Murthy
,
M. Tanvir
Rahman
,
Tiila-Riikka
Kiema
,
Shruthi
Sridhar
,
Gabriele
Cordara
,
Subhadra
Dalwani
,
Rajaram
Venkatesan
,
Jaime
Prilusky
,
Orly
Dym
,
Lari
Lehtio
,
M. Kristian
Koski
,
Alun W.
Ashton
,
Joel L.
Sussman
,
Rikkert K.
Wierenga
Open Access
Abstract: The web-based IceBear software is a versatile tool to monitor the results of crystallization experiments and is designed to facilitate supervisor and student communications. It also records and tracks all relevant information from crystallization setup to PDB deposition in protein crystallography projects. Fully automated data collection is now possible at several synchrotrons, which means that the number of samples tested at the synchrotron is currently increasing rapidly. Therefore, the protein crystallography research communities at the University of Oulu, Weizmann Institute of Science and Diamond Light Source have joined forces to automate the uploading of sample metadata to the synchrotron. In IceBear, each crystal selected for data collection is given a unique sample name and a crystal page is generated. Subsequently, the metadata required for data collection are uploaded directly to the ISPyB synchrotron database by a shipment module, and for each sample a link to the relevant ISPyB page is stored. IceBear allows notes to be made for each sample during cryocooling treatment and during data collection, as well as in later steps of the structure determination. Protocols are also available to aid the recycling of pins, pucks and dewars when the dewar returns from the synchrotron. The IceBear database is organized around projects, and project members can easily access the crystallization and diffraction metadata for each sample, as well as any additional information that has been provided via the notes. The crystal page for each sample connects the crystallization, diffraction and structural information by providing links to the IceBear drop-viewer page and to the ISPyB data-collection page, as well as to the structure deposited in the Protein Data Bank.
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Feb 2021
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I03-Macromolecular Crystallography
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Diamond Proposal Number(s):
[26302, 24732]
Abstract: The peroxisomal multifunctional enzyme type 1 (MFE1) catalyzes two successive reactions in the β-oxidation cycle: the 2E-enoyl-CoA hydratase (ECH) and NAD+-dependent 3S-hydroxyacyl-CoA dehydrogenase (HAD) reactions. MFE1 is a monomeric enzyme that has five domains. The N-terminal part (domains A and B) adopts the crotonase fold and the C-terminal part (domains C, D and E) adopts the HAD fold. A new crystal form of MFE1 has captured a conformation in which both active sites are noncompetent. This structure, at 1.7 Å resolution, shows the importance of the interactions between Phe272 in domain B (the linker helix; helix H10 of the crotonase fold) and the beginning of loop 2 (of the crotonase fold) in stabilizing the competent ECH active-site geometry. In addition, protein crystallographic binding studies using optimized crystal-treatment protocols have captured a structure with both the 3-ketodecanoyl-CoA product and NAD+ bound in the HAD active site, showing the interactions between 3-ketodecanoyl-CoA and residues of the C, D and E domains. Structural comparisons show the importance of domain movements, in particular of the C domain with respect to the D/E domains and of the A domain with respect to the HAD part. These comparisons suggest that the N-terminal part of the linker helix, which interacts tightly with domains A and E, functions as a hinge region for movement of the A domain with respect to the HAD part.
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Dec 2020
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