[Show abstract][Hide abstract] ABSTRACT: Malaria is caused by a protozoan parasite that replicates within an intraerythrocytic parasitophorous vacuole. Release (egress) of malaria merozoites from the host erythrocyte is a highly regulated and calcium-dependent event that is critical for disease progression. Minutes before egress, an essential parasite serine protease called SUB1 is discharged into the parasitophorous vacuole, where it proteolytically processes a subset of parasite proteins that play indispensable roles in egress and invasion. Here we report the first crystallographic structure of Plasmodium falciparum SUB1 at 2.25 Å, in complex with its cognate prodomain. The structure highlights the basis of the calcium dependence of SUB1, as well as its unusual requirement for interactions with substrate residues on both prime and non-prime sides of the scissile bond. Importantly, the structure also reveals the presence of a solvent-exposed redox-sensitive disulphide bridge, unique among the subtilisin family, that likely acts as a regulator of protease activity in the parasite.
[Show abstract][Hide abstract] ABSTRACT: Insulin receptor signalling has a central role in mammalian biology, regulating cellular metabolism, growth, division, differentiation and survival. Insulin resistance contributes to the pathogenesis of type 2 diabetes mellitus and the onset of Alzheimer's disease; aberrant signalling occurs in diverse cancers, exacerbated by cross-talk with the homologous type 1 insulin-like growth factor receptor (IGF1R). Despite more than three decades of investigation, the three-dimensional structure of the insulin-insulin receptor complex has proved elusive, confounded by the complexity of producing the receptor protein. Here we present the first view, to our knowledge, of the interaction of insulin with its primary binding site on the insulin receptor, on the basis of four crystal structures of insulin bound to truncated insulin receptor constructs. The direct interaction of insulin with the first leucine-rich-repeat domain (L1) of insulin receptor is seen to be sparse, the hormone instead engaging the insulin receptor carboxy-terminal α-chain (αCT) segment, which is itself remodelled on the face of L1 upon insulin binding. Contact between insulin and L1 is restricted to insulin B-chain residues. The αCT segment displaces the B-chain C-terminal β-strand away from the hormone core, revealing the mechanism of a long-proposed conformational switch in insulin upon receptor engagement. This mode of hormone-receptor recognition is novel within the broader family of receptor tyrosine kinases. We support these findings by photo-crosslinking data that place the suggested interactions into the context of the holoreceptor and by isothermal titration calorimetry data that dissect the hormone-insulin receptor interface. Together, our findings provide an explanation for a wealth of biochemical data from the insulin receptor and IGF1R systems relevant to the design of therapeutic insulin analogues.
[Show abstract][Hide abstract] ABSTRACT: The paper reports the purification and characterization of the first penicillin acylase from Bacillus subtilis. YxeI, the protein annotated as hypothetical, coded by the gene yxeI in the open reading frame between iol and hut operons in B. subtilis was cloned and expressed in Eshcherichia coli, purified and characterized. The purified protein showed measurable penicillin acylase activity with penicillin V. The enzyme was a homotetramer of 148 kDa. The apparent K(m) of the enzyme for penicillin V and the synthetic substrate 2-nitro-5-(phenoxyacetamido)-benzoic acid was 40 mM and 0.63 mM, respectively, and the association constants were 8.93×10(2) M(-1) and 2.51×10(5) M(-1), respectively. It was inhibited by cephalosporins and conjugated bile salts, substrates of the closely related bile acid hydrolases. It had good sequence homology with other penicillin V acylases and conjugated bile acid hydrolases, members of the Ntn hydrolase family. The N-terminal nucleophile was a cysteine which is revealed by a simple removal of N-formyl-methionine. The activity of the protein was affected by high temperature, acidic pH and the presence of the denaturant guanidine hydrochloride.
International journal of biological macromolecules 01/2012; 50(1):25-30. DOI:10.1016/j.ijbiomac.2011.09.018 · 2.86 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Many critical cellular functions are performed by multisubunit circular protein oligomers whose internal geometry has evolved to meet functional requirements. The subunit number is arguably the most critical parameter of a circular protein assembly, affecting the internal and external diameters of the assembly and often impacting on the protein's function. Although accurate structural information has been obtained for several circular proteins, a lack of accurate information on alternative oligomeric states has prevented engineering such transitions. In this study we used the bacterial transcription regulator TRAP as a model system to investigate the features that define the oligomeric state of a circular protein and to question how the subunit number could be manipulated.
We find that while Bacillus subtilis and Bacillus stearothermophilus TRAP form 11-subunit oligomers, the Bacillus halodurans TRAP exclusively forms 12-subunit assemblies. Significantly, the two states of TRAP are related by a simple rigid body rotation of individual subunits around inter-subunit axes. We tested if such a rotation could be induced by insertion or deletion mutations at the subunit interface. Using wild type 11-subunit TRAP, we demonstrate that removal of five C-terminal residues at the outer side of the inter-subunit axis or extension of an amino acid side chain at the opposite, inner side, increased the subunit number from 11 to 12. Our findings are supported by crystal structures of TRAP oligomers and by native mass spectrometry data.
The subunit number of the TRAP oligomer can be manipulated by introducing deletion or addition mutations at the subunit interface. An analysis of available and emerging structural data on alternative oligomeric states indicates that the same principles may also apply to the subunit number of other circular assemblies suggesting that the deletion/addition approach could be used generally to engineer transitions between different oligomeric states.
PLoS ONE 10/2011; 6(10):e25296. DOI:10.1371/journal.pone.0025296 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Scientific contact lies at the heart of research and that between China and the U.K. is an important example of how it can come about. In 1911, when the Biochemical Society began, U.K. science was developing fast with profound discoveries in physics (the Rutherford atomic model) and biochemistry (the discovery of vitamins). In China, however, there was great social and political instability and a revolution. Since then, the turbulence of two world wars and a variety of deep global political tensions meant that the contacts between China and U.K. did not reflect the prodigious growth of biochemistry. There was, however, one particular and remarkable contact, that made by Joseph Needham, an outstanding biochemist. He visited China between 1943 and 1946, contacting many Chinese universities that were severely dislocated by war. Showing remarkable diplomatic abilities, Needham managed to arrange delivery of research and teaching equipment. His activities helped the universities to carry out their functions under near-impossible conditions and reminded them that they had friends abroad. Most remarkably, Joseph Needham developed an extraordinary grasp of Chinese culture, science and history and he opened the West to the extent and importance of Chinese science. Formal scientific and intellectual contacts between the scientific academic bodies in China and U.K., notably the Chinese Academy of Science and the Royal Society, resumed after British recognition of the Chinese Communist government in 1950. The delegations included outstanding scientists in biochemistry and related disciplines. Research activities, such as that concerning influenza, were soon established, whereas institutions, such as the Royal Society and the Wellcome Trust, acted a little later to support research. The outcomes have been long-term collaborations in such areas as insulin structure and function. There are now numerous joint activities in biochemistry and biomedicine supported by the MRC (Medical Research Council), BBSRC (Biotechnology and Biological Sciences Research Council), NERC (Natural Environment Research Council), EPSRC (Engineering and Physical Sciences Research Council) and UKRC (UK Research Councils). The present contacts and the associated research are very considerable and growing. It is clear that biochemistry in both countries has much to offer each other, and there is every reason to believe that these contacts will continue to expand in the future.
Biochemical Society Transactions 10/2011; 39(5):1313-22. DOI:10.1042/BST0391313 · 3.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Insulin is a key protein hormone that regulates blood glucose levels and, thus, has widespread impact on lipid and protein metabolism. Insulin action is manifested through binding of its monomeric form to the Insulin Receptor (IR). At present, however, our knowledge about the structural behavior of insulin is based upon inactive, multimeric, and storage-like states. The active monomeric structure, when in complex with the receptor, must be different as the residues crucial for the interactions are buried within the multimeric forms. Although the exact nature of the insulin's induced-fit is unknown, there is strong evidence that the C-terminal part of the B-chain is a dynamic element in insulin activation and receptor binding. Here, we present the design and analysis of highly active (200-500%) insulin analogues that are truncated at residue 26 of the B-chain (B(26)). They show a structural convergence in the form of a new beta-turn at B(24)-B(26). We propose that the key element in insulin's transition, from an inactive to an active state, may be the formation of the beta-turn at B(24)-B(26) associated with a trans to cis isomerisation at the B(25)-B(26) peptide bond. Here, this turn is achieved with N-methylated L-amino acids adjacent to the trans to cis switch at the B(25)-B(26) peptide bond or by the insertion of certain D-amino acids at B(26). The resultant conformational changes unmask previously buried amino acids that are implicated in IR binding and provide structural details for new approaches in rational design of ligands effective in combating diabetes.
Proceedings of the National Academy of Sciences 02/2010; 107(5):1966-70. DOI:10.1073/pnas.0911785107 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The two hemoglobin structures determined by Max Perutz, the liganded R-state, which has high oxygen affinity, and the unliganded T-state with low oxygen affinity, were landmarks in molecular and structural biology (Perutz and Lehman, Nature 1968, 219, 902-909; Bolton and Perutz, Nature 1970, 28, 551-552; Perutz et al., Nature 1968, 219, 131-139). They provided the basis of a structural mechanism that connected beautifully to the theory of cooperativity in protein systems, formulated at about the same time by Monod et al. (J Mol Biol 1965, 12, 88-1118). Over the last 40 years there have been extensive biochemical and structural studies on hemoglobin's structure and the mechanisms that govern its co-operativity, specificity, and other physiological properties. There are still however a number of unresolved issues over the molecule's properties, for example the mechanism responsible for the affects of pH on oxygen affinity, i.e., the Bohr and Root effects. In this communication the differences in the geometry at the a-heme of unliganded and liganded human and the Antarctic fish (Trematomus) hemoglobin will be described and their relevance to affinity considered.
[Show abstract][Hide abstract] ABSTRACT: Formation of PrP aggregates is considered to be a characteristic event in the pathogenesis of TSE diseases, accompanied by brain inflammation and neurodegeneration. Factors identified as contributing to aggregate formation are of interest as potential therapeutic targets. We report that in vitro proteolysis of ovine PrP(94-233) (at neutral pH and in the absence of denaturants) by the protease cathepsin S, a cellular enzyme that also shows enhanced expression in pathogenic conditions, occurs selectively in the region 135-156. This results in an unusually efficient, concentration-dependent conformational conversion of a large subfragment of PrP(94-233) into a soluble beta-structured oligomeric intermediate species, that readily forms a thioflavin-T-positive aggregate. N-terminal sequencing of the proteolysis fragments shows the aggregating species have marked sequence similarities to truncated PrP variants known to confer unusually severe pathogenicity when transgenically expressed in PrP(o/o) mice. Circular dichroism analysis shows that PrP fragments 138-233, 144-233 and 156-233 are significantly less stable than PrP(94-233). This implies an important structural contribution of the beta1 sequence within the globular domain of PrP. We propose that the removal or detachment of the beta1 sequence enhances beta-oligomer formation from the globular domain, leading to aggregation. The cellular implications are that specific proteases may have an important role in the generation of membrane-bound, potentially toxic, beta-oligomeric PrP species in pre-amyloid states of prion diseases. Such species may induce cell death by lysis, and also contribute to the transport of PrP to neuronal targets with subsequent amplification of pathogenic effects.
Biophysics of Structure and Mechanism 10/2008; 38(2):209-18. DOI:10.1007/s00249-008-0371-3 · 2.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Recent advances in computer hardware and software have led to the development of increasingly successful molecular simulations of protein structural dynamics that are intrinsic to biological processes. These simulations have resulted in models that increasingly agree with experimental observations, suggest new experiments and provide insights into biological mechanisms. Used in combination with data obtained with sophisticated experimental techniques, simulations are helping us to understand biological complexity at the atomic and molecular levels and are giving promising insights into the genetic, thermodynamic and functional/mechanistic behaviour of biological processes. Here, we highlight some examples of such approaches that illustrate the current state and potential of the field of molecular simulation.
[Show abstract][Hide abstract] ABSTRACT: The malaria parasite proliferates in the bloodstream of its vertebrate host by invading and replicating within erythrocytes. To achieve successful invasion, a number of discrete and essential events need to take place at the parasite-host cell interface. Erythrocyte-binding antigen 175 (EBA-175) is a member of a family of Plasmodium falciparum erythrocyte-binding proteins involved in the formation of a tight junction, a necessary step in invasion. Here we present the crystal structure of EBA-175 region VI (rVI), a cysteine-rich domain that is highly conserved within the protein family and is essential for EBA-175 trafficking. The structure was solved by selenomethionine single-wavelength anomalous dispersion at 1.8 A resolution. It reveals a homodimer, containing in each subunit a compact five-alpha-helix core that is stabilized by four conserved disulfide bridges. rVI adopts a novel fold that is likely conserved across the protein family, indicating a conserved function. It shows no similarity to the Duffy-binding-like domains of EBA-175 involved in erythrocyte binding, indicating a distinct role. Remarkably, rVI possesses structural features related to the KIX-binding domain of the coactivator CREB-binding protein, supporting the binding and trafficking roles that have been ascribed to it and providing a rational basis for further experimental investigation of its function.
[Show abstract][Hide abstract] ABSTRACT: The determination of the structure of the insulin hexamer has made it possible to design amino acid substitutions which alter
insulin’s activity and association properties. This has given insight into insulin’s biological function and has led to improvement
in clinical preparations of insulin.
[Show abstract][Hide abstract] ABSTRACT: Conformational transitions and functional stability of the bile salt hydrolase (BSH; cholylglycine EC: 22.214.171.124) from Bifidobacterium longum (BlBSH) cloned and expressed in E. coli were studied under thermal, chemical and pH-mediated denaturation conditions using fluorescence and CD spectroscopy. Thermal and Gdn-HCl-mediated denaturation of BlBSH is a multistep process of inactivation and unfolding. The inactivation and unfolding of the enzyme was found to be irreversible. Enzyme activity seems sensitive to even minor conformational changes at the active site. Thermal denaturation as such did not result in any insoluble protein aggregates. However, on treating with 0.25 - 1 M Gdn-HCl the enzyme showed increasing aggregation at temperatures of 40 - 55 degrees C indicating more complex structural changes taking place in the presence of chemical denaturants. The enzyme secondary structure was still intact at acidic pH (pH 1 - 3). The perturbation in the tertiary structure at the acidic pH was detected through freshly formed solvent exposed hydrophobic patches on the enzyme. These changes could be due to the formation of an acid-induced molten globule-like state.
International Union of Biochemistry and Molecular Biology Life 03/2007; 59(2):118-25. DOI:10.1080/15216540701245014 · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Bile salt hydrolase (BSH) is an enzyme produced by the intestinal microflora that catalyzes the deconjugation of glycine- or taurine-linked bile salts. The crystal structure of BSH reported here from Bifidobacterium longum reveals that it is a member of N-terminal nucleophil hydrolase structural superfamily possessing the characteristic alphabetabetaalpha tetra-lamellar tertiary structure arrangement. Site-directed mutagenesis of the catalytic nucleophil residue, however, shows that it has no role in zymogen processing into its corresponding active form. Substrate specificity was studied using Michaelis-Menten and inhibition kinetics and fluorescence spectroscopy. These data were compared with the specificity profile of BSH from Clostridium perfrigens and pencillin V acylase from Bacillus sphaericus, for both of which the three-dimensional structures are available. Comparative analysis shows a gradation in activity toward common substrates, throwing light on a possible common route toward the evolution of pencillin V acylase and BSH.
[Show abstract][Hide abstract] ABSTRACT: The nature of the factors leading to the conversion of the cellular prion protein (PrP(C)) into its amyloidogenic isoform (PrP(Sc)) is still matter of debate in the field of structural biology. The NMR structures of non-mammalian PrP(C) (non-mPrP) from frog, chicken and turtle [Calzolai, L., Lysek, D.A., Perez, D.R., Guntert, P. and Wuthrich, K. (2005) Prion protein NMR structures of chickens, turtles, and frogs. Proc. Natl. Acad. Sci. USA 102, 651-655] have provided some new and valuable information on the scaffolding elements that preserve the PrP(C) folding, despite their low sequence identity with the mammalian prions (mPrP). The present molecular dynamics study of non-mPrP(C) focuses on the hydration properties of these proteins in comparison with the mammalian ones. The data reveal new insights in the PrP hydration and focus on the implications for PrP(C) folding stability and its propensity for interactions. In addition, for the first time, a role in disfavoring the PrP(C) aggregation is suggested for a conserved beta-bulge which is stabilized by the local hydration.
[Show abstract][Hide abstract] ABSTRACT: Computer simulations at the atomic level have arrived at a stage where they provide realistic modeling of flexibility in proteins (and the mobility of their associated solvent) that is important in understanding the nature of molecular motions. This can now be extended to the molecular and atomic motions that are associated with protein mechanisms. Moreover, the derived data agree reasonably accurately with experimental measurements of several kinetic and thermodynamic parameters. Fundamental insights emerge on the roles that this intrinsic flexibility plays in the thermodynamic characteristics of macromolecules in solution; these equip the investigator to probe the consequences of cognate interactions and ligand binding on entropy and enthalpy. Thus simulations can now provide a powerful tool for investigating protein mechanisms that complements the existing and the emerging experimental techniques.
Cellular and Molecular Life Sciences CMLS 02/2006; 63(2):207-19. DOI:10.1007/s00018-005-5236-7 · 5.81 Impact Factor