[Show abstract][Hide abstract] ABSTRACT: The influenza virus neuraminidase (NA) is essential for the virus life cycle. The rise of resistance mutations against current antiviral therapies has increased the need for the development of novel inhibitors. Recent efforts have targeted a cavity adjacent to the catalytic site (the 150-cavity) in addition to the primary catalytic subsite in order to increase specificity and reduce the likelihood of resistance. This study details structural and in vitro analyses of a class of inhibitors that bind uniquely in both subsites. Crystal structures of three inhibitors show occupation of the 150-cavity in two distinct and novel binding modes. We believe these are the first nanomolar inhibitors of NA to be characterized in this way. Furthermore, we show that one inhibitor, binding within the catalytic site, offers reduced susceptibility to known resistance mutations via increased flexibility of a pendant pentyloxy group and the ability to pivot about a strong hydrogen-bonding network.
[Show abstract][Hide abstract] ABSTRACT: A series of C3 O-functionalized 2-acetamido-2-deoxy-Δ(4)-β-d-glucuronides were synthesized to explore noncharge interactions in subsite 2 of the influenza virus sialidase active site. In complex with A/N8 sialidase, the parent compound (C3 OH) inverts its solution conformation to bind with all substituents well positioned in the active site. The parent compound inhibits influenza virus sialidase at a sub-μM level; the introduction of small alkyl substituents or an acetyl group at C3 is also tolerated.
[Show abstract][Hide abstract] ABSTRACT: Novel 3-C-alkylated-Neu5Ac2en derivatives have been designed to target the expanded active site cavity of influenza virus sialidases with an open 150-loop, currently seen in X-ray crystal structures of influenza A virus group-1 (N1, N4, N5, N8), but not group-2 (N2, N9), sialidases. The compounds show selectivity for inhibition of H5N1 and pdm09 H1N1 sialidases over an N2 sialidase, providing evidence of the relative 150-loop flexibility of these sialidases. In a complex with N8 sialidase, the C3 substituent of 3-phenylally-Neu5Ac2en occupies the 150-cavity while the central ring and the remaining substituents bind the active site as seen for the unsubstituted template. This new class of inhibitors, which can 'trap' the open 150-loop form of the sialidase, should prove useful as probes of 150-loop flexibility.
[Show abstract][Hide abstract] ABSTRACT: The effector domain (ED) of the influenza virus virulence factor NS1 is capable of interaction with a variety of cellular and viral targets, although regulation of these events is poorly understood. Introduction of a W187A mutation into the ED abolishes dimer formation; however, strand-strand interactions between mutant NS1 ED monomers have been observed in two previous crystal forms. A new condition for crystallization of this protein [0.1 M Bis-Tris pH 6.0, 0.2 M NaCl, 22%(w/v) PEG 3350, 20 mM xylitol] was discovered using the hanging-drop vapour-diffusion method. Diffraction data extending to 1.8 Å resolution were collected from a crystal grown in the presence of 40 mM thieno[2,3-b]pyridin-2-ylmethanol. It was observed that there is conservation of the strand-strand interface in crystals of this monomeric NS1 ED in three different space groups. This observation, coupled with conformational changes in the interface region, suggests a potential role for β-sheet augmentation in NS1 function.
Acta Crystallographica Section F Structural Biology and Crystallization Communications 08/2011; 67(Pt 8):858-61. DOI:10.1107/S1744309111019312 · 0.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Influenza virus sialidase has an essential role in the virus' life cycle. Two distinct groups of influenza A virus sialidases have been established, that differ in the flexibility of the '150-loop', providing a more open active site in the apo form of the group-1 compared to group-2 enzymes. In this study we show, through a multidisciplinary approach, that novel sialic acid-based derivatives can exploit this structural difference and selectively inhibit the activity of group-1 sialidases. We also demonstrate that group-1 sialidases from drug-resistant mutant influenza viruses are sensitive to these designed compounds. Moreover, we have determined, by protein X-ray crystallography, that these inhibitors lock open the group-1 sialidase flexible 150-loop, in agreement with our molecular modelling prediction. This is the first direct proof that compounds may be developed to selectively target the pandemic A/H1N1, avian A/H5N1 and other group-1 sialidase-containing viruses, based on an open 150-loop conformation of the enzyme.
[Show abstract][Hide abstract] ABSTRACT: The tenovins and cambinol are two classes of sirtuin inhibitor that exhibit antitumor activity in preclinical models. This report describes modifications to the core structure of cambinol, in particular by incorporation of substituents at the N1-position, which lead to increased potency and modified selectivity. These improvements have been rationalized using molecular modeling techniques. The expected functional selectivity in cells was also observed for both a SIRT1 and a SIRT2 selective analog.
[Show abstract][Hide abstract] ABSTRACT: The Streptococcus pneumoniae genomes encode up to three sialidases (or neuraminidases), NanA, NanB and NanC, which are believed to be involved in removing sialic acid from host cell surface glycans, thereby promoting colonization of the upper respiratory tract. Here, we present the crystal structure of NanB to 1.7 A resolution derived from a crystal grown in the presence of the buffer Ches (2-N-cyclohexylaminoethanesulfonic acid). Serendipitously, Ches was found bound to NanB at the enzyme active site, and was found to inhibit NanB with a K(i) of approximately 0.5 mM. In addition, we present the structure to 2.4 A resolution of NanB in complex with the transition-state analogue Neu5Ac2en (2-deoxy-2,3-dehydro-N-acetyl neuraminic acid), which inhibits NanB with a K(i) of approximately 0.3 mM. The sulphonic acid group of Ches and carboxylic acid group of Neu5Ac2en interact with the arginine triad of the active site. The cyclohexyl group of Ches binds in the hydrophobic pocket of NanB occupied by the acetamidomethyl group of Neu5Ac2en. The topology around the NanB active site suggests that the enzyme would have a preference for alpha2,3-linked sialoglycoconjugates, which is confirmed by a kinetic analysis of substrate binding. NMR studies also confirm this preference and show that, like the leech sialidase, NanB acts as an intramolecular trans-sialidase releasing Neu2,7-anhydro5Ac. All three pneumoccocal sialidases possess a carbohydrate-binding domain that is predicted to bind sialic acid. These studies provide support for a possible differential role for NanB compared to NanA in pneumococcal virulence.
[Show abstract][Hide abstract] ABSTRACT: The crystal structure of citrate synthase from the thermophilic Archaeon Sulfolobus solfataricus (optimum growth temperature = 85 degrees C) has been determined, extending the number of crystal structures of citrate synthase from different organisms to a total of five that span the temperature range over which life exists (from psychrophile to hyperthermophile). Detailed structural analysis has revealed possible molecular mechanisms that determine the different stabilities of the five proteins. The key to these mechanisms is the precise structural location of the additional interactions. As one ascends the temperature ladder, the subunit interface of this dimeric enzyme and loop regions are reinforced by complex electrostatic interactions, and there is a reduced exposure of hydrophobic surface. These observations reveal a progressive pattern of stabilization through multiple additional interactions at solvent exposed, loop and interfacial regions.
European Journal of Biochemistry 01/2003; 269(24):6250-60. DOI:10.1046/j.1432-1033.2002.03344.x · 3.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Crystals of Sso10b from the hyperthermophilic archaeon Sulfolobus solfataricus have been grown that diffract to 2.6 A resolution. The protein is a highly abundant non-specific double-stranded DNA-binding protein, conserved throughout the archaea, that has been implicated in playing a role in the architecture of archaeal chromatin.
[Show abstract][Hide abstract] ABSTRACT: Comparative structural studies on proteins derived from organisms with growth optima ranging from 15 to 100°C are beginning to shed light on the mechanisms of protein thermoadaptation. One means of sustaining hyperthermostability is for proteins to exist in higher oligomeric forms than their mesophilic homologues. Triosephosphate isomerase (TIM) is one of the most studied enzymes, whose fold represents one of nature’s most common protein architectures. Most TIMs are dimers of approximately 250 amino acid residues per monomer. Here, we report the 2.7 Å resolution crystal structure of the extremely thermostable TIM from Pyrococcus woesei, a hyperthermophilic archaeon growing optimally at 100°C, representing the first archaeal TIM structure. P. woesei TIM exists as a tetramer comprising monomers of only 228 amino acid residues. Structural comparisons with other less thermostable TIMs show that although the central β-barrel is largely conserved, severe pruning of several helices and truncation of some loops give rise to a much more compact monomer in the small hyperthermophilic TIM. The classical TIM dimer formation is conserved in P. woesei TIM. The extreme thermostability of PwTIM appears to be achieved by the creation of a compact tetramer where two classical TIM dimers interact via an extensive hydrophobic interface. The tetramer is formed through largely hydrophobic interactions between some of the pruned helical regions. The equivalent helical regions in less thermostable dimeric TIMs represent regions of high average temperature factor. The PwTIM seems to have removed these regions of potential instability in the formation of the tetramer. This study of PwTIM provides further support for the role of higher oligomerisation states in extreme thermal stabilisation.
[Show abstract][Hide abstract] ABSTRACT: Crystals have been grown of 2-keto-3-deoxygluconate aldolase (KDG aldolase) from the hyperthermophilic archaeon Sulfolobus solfataricus that diffract to 2.2 A resolution. The enzyme catalyses the reversible aldol cleavage of 2-keto-3-dexoygluconate to pyruvate and glyceraldehyde, the third step of a modified non-phosphorylated Entner-Doudoroff pathway of glucose oxidation. S. solfataricus grows optimally at 353 K and the enzyme itself has a half-life of 2.5 h at 373 K. Knowledge of the crystal structure of KDG aldolase will further understanding of the basis of protein hyperthermostability and create a target for site-directed mutagenesis of active-site residues, with the aim of altering substrate specificity. Three crystal forms have been obtained: orthorhombic crystals of space group P2(1)2(1)2(1), which diffract to beyond 2.15 A, monoclinic crystals of space group C2, which diffract to 2.2 A, and cubic crystals of space group P4(2)32, which diffract to 3.4 A.
[Show abstract][Hide abstract] ABSTRACT: The kinetics and mechanism of the citrate synthase from a moderate thermophile, Thermoplasma acidophilum (TpCS), are compared with those of the citrate synthase from a mesophile, pig heart (PCS). All discrete steps in the mechanistic sequence of PCS can be identified in TpCS. The catalytic strategies identified in PCS, destabilization of the oxaloacetate substrate carbonyl and stabilization of the reactive species, acetyl-CoA enolate, are present in TpCS. Conformational changes, which allow the enzyme to efficiently catalyze both condensation of acetyl-CoA thioester and subsequently hydrolysis of citryl-CoA thioester within the same active site, occur in both enzymes. However, significant differences exist between the two enzymes. PCS is a characteristically efficient enzyme: no internal step is clearly rate-limiting and the condensation step is readily reversible. TpCS is a less efficient catalyst. Over a broad temperature range, inadequate stabilization of the transition state for citryl-CoA hydrolysis renders this step nearly rate-limiting for the forward reaction of TpCS. Further, excessive stabilization of the citryl-CoA intermediate renders the condensation step nearly irreversible. Values of substrate and solvent deuterium isotope effects are consistent with the kinetic model. Near its temperature optimum (70 degrees C), there is a modest increase in the reversibility of the condensation step for TpCS, but reversibility still falls short of that shown by PCS at 37 degrees C. The root cause of the catalytic inefficiency of TpCS may lie in the lack of protein flexibility imposed by the requirement for thermal stability of the protein itself or its temperature-labile substrate, oxaloacetate.
[Show abstract][Hide abstract] ABSTRACT: A homology-modelled structure of dihydrolipoamide dehydrogenase from the halophilic archaeon, Haloferax volcanii, has been generated using the crystal structure of the enzyme from Pseudomonas fluorescens. Analysis of the halophilic enzyme structure identified a potential K+-binding site comprising four co-ordinated glutamate residues (E423 and E426 from each monomer) at the subunit interface of the dimeric protein. Whilst E426 is conserved throughout non-halophilic dihydrolipoamide dehydrogenases, E423 is only present in the halophilic enzyme. Four site-directed mutations of the Haloferax dihydrolipoamide dehydrogenase have been made (E423D, E423Q, E423S, and E423A) and the recombinant mutants expressed and characterised. From an analysis of their kinetic properties, salt-dependent activities and thermal stabilities, it is concluded that this site has an important influence on the halophilicity of the enzyme. The findings support the view that the arrangement and interaction of the negatively charged amino acids are as important as the total net charge in determining the adaptation of proteins to high salt concentrations.
European Journal of Biochemistry 10/1997; 248(2):362-8. DOI:10.1111/j.1432-1033.1997.00362.x · 3.58 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The crystal structure of the closed form of citrate synthase, with citrate and CoA bound, from the hyperthermophilic Archaeon Pyrococcus furiosus has been determined to 1.9 A. This has allowed direct structural comparisons between the same enzyme from organisms growing optimally at 37 degrees C (pig), 55 degrees C (Thermoplasma acidophilum) and now 100 degrees C (Pyrococcus furiosus). The three enzymes are homodimers and share a similar overall fold, with the dimer interface comprising primarily an eight alpha-helical sandwich of four antiparallel pairs of helices. The active sites show similar modes of substrate binding; moreover, the structural equivalence of the amino acid residues implicated in catalysis implies that the mechanism proceeds via the same acid-base catalytic process. Given the overall structural and mechanistic similarities, it has been possible to make detailed structural comparisons between the three citrate synthases, and a number of differences can be identified in passing from the mesophilic to thermophilic to hyperthermophilic citrate synthases. The most significant of these are an increased compactness of the enzyme, a more intimate association of the subunits, an increase in intersubunit ion pairs, and a reduction in thermolabile residues. Compactness is achieved by the shortening of a number of loops, an increase in the number of atoms buried from solvent, an optimized packing of side chains in the interior, and an absence of cavities. The intimate subunit association in the dimeric P. furiosus enzyme is achieved by greater complementarity of the monomers and by the C-terminal region of each monomer folding over the surface of the other monomer, in contrast to the pig enzyme where the C-terminus has a very different fold. The increased number of intersubunit ion pairs is accompanied by an increase in the number involved in networks. Interestingly, all loop regions in the P. furiosus enzyme either are shorter or contain additional ion pairs compared with the pig enzyme. The possible relevance of these structural features to enzyme hyperthermostability is discussed.
[Show abstract][Hide abstract] ABSTRACT: The gene encoding the enzyme citrate synthase has been cloned and sequenced from the hyperthermophilic Archaeon Pyrococcus furiosus, and the derived amino acid sequence has been phylogenetically compared with citrate synthases from archaeal, bacterial and eukaryal organisms. The gene has been over-expressed in Escherichia coli to produce an active enzyme that has then been characterized with respect to its kinetic, oligomeric and hyperthermostable properties. A structurally-based sequence alignment was made to the citrate synthase from the thermophilic Archaeon Thermoplasma acidophilum, the crystal structure of which we have determined recently. From this alignment, a homology-modelled structure for the P.furiosus citrate synthase was generated and analysed.
Protein engineering 07/1995; 8(6):583-92. DOI:10.1093/protein/8.6.583
[Show abstract][Hide abstract] ABSTRACT: Citrate synthases from both thermophilic and halophilic Archaea have been purified to homogeneity using affinity chromatography on Matrex Gel Red A and elution with a combination of substrate (oxaloacetate) and product (coenzyme A). In a number of cases, purification from cell-extract to protein suitable for N-terminal sequencing can be achieved by this single-step procedure. The method is particularly useful in the rapid purification of a thermophilic archaeal citrate synthase from a cloned gene expressed in a mesophilic host.
[Show abstract][Hide abstract] ABSTRACT: Single crystals of citrate synthase from the Archaeon Thermoplasma acidophilum were obtained in two forms using the hanging drop vapour diffusion method and polyethylene glycol 3350 as precipitant. Type 1 crystals belong to the orthorhombic space group P222(1), with unit cell dimensions a = 80.9 A, b = 103.8 A, c = 98.3 A and one dimer in the asymmetric unit. Type 2 crystals belong to the monoclinic space group P2(1), with unit cell dimensions a = 53.8 A, b = 173.8 A, c = 86.7 A and beta = 97.1 degrees and two dimers in the asymmetric unit.