I02-Macromolecular Crystallography
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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.
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Jan 2010
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I04-Macromolecular Crystallography
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Open Access
Abstract: The porins OmpF and OmpC are trimeric β-barrel proteins with narrow channels running through each monomer that exclude molecules > 600 Da while mediating the passive diffusion of small nutrients and metabolites across the Gram-negative outer membrane (OM). Here, we elucidate the mechanism by which an entire soluble protein domain (> 6 kDa) is delivered through the lumen of such porins. Following high-affinity binding to the vitamin B12 receptor in Escherichia coli, the bacteriocin ColE9 recruits OmpF or OmpC using an 83-residue intrinsically unstructured translocation domain (IUTD) to deliver a 16-residue TolB-binding epitope (TBE) in the center of the IUTD to the periplasm where it triggers toxin entry. We demonstrate that the IUTD houses two OmpF-binding sites, OBS1 (residues 2–18) and OBS2 (residues 54–63), which flank the TBE and bind with Kds of 2 and 24 μM, respectively, at pH 6.5 and 25 ºC. We show the two OBSs share the same binding site on OmpF and that the colicin must house at least one of them for antibiotic activity. Finally, we report the structure of the OmpF-OBS1 complex that shows the colicin bound within the porin lumen spanning the membrane bilayer. Our study explains how colicins exploit porins to deliver epitope signals to the bacterial periplasm and, more broadly, how the inherent flexibility and narrow cross-sectional area of an IUP domain can endow it with the ability to traverse a biological membrane via the constricted lumen of a β-barrel membrane protein.
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Dec 2010
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Open Access
Abstract: 328366 Apart from its role in insulin receptor (IR) activation, the C-terminus of the B-chain of insulin is also responsible for the formation of insulin dimers. The dimerisation of insulin plays an important role in the endogenous delivery of the hormone and in the administration of insulin to patients. Here, we investigated insulin analogues with selective N-methylations of peptide bond amides at positions B24, B25 or B26 to delineate their structural and functional contribution to the dimer interface. All N-methylated analogues showed impaired binding affinities to IR, which suggests a direct IR-interacting role for the respective amide hydrogens. The dimerisation capabilities of analogues were investigated by isothermal microcalorimetry. Selective N-methylations of B24, B25 or B26 amides resulted in reduced dimerisation abilities compared to native insulin (Kdiss = 8.8 μM). Interestingly, while the N-methylation in [NMeTyrB26]-insulin or [NMePheB24]-insulin resulted in Kd values of 142 and 587 μM, respectively, the [NMePheB25]-insulin did not form dimers even at high concentrations. This effect may be attributed to the loss of intra-molecular hydrogen bonding between NHB25 and COA19, which connects the B-chain β-strand to the core of the molecule. The release of the B-chain β-strand from this hydrogen bond-lock may result in its higher mobility, thereby shifting solution equilibrium towards the monomeric state of the hormone. The study was complemented by analyses of two novel analogue crystal structures. All examined analogues crystallised only in the most stable R6-form of insulin oligomers (even if the dimer interface was totally disrupted), confirming the role of R6-specific intra/inter-molecular interactions for hexamer stability.
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Sep 2011
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-1-Macromolecular Crystallography (fixed wavelength)
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Abstract: Design of inhibitors for N-myristoyltransferase (NMT), an enzyme responsible for protein trafficking in Plasmodium falciparum, the most lethal species of parasites that cause malaria, is described. Chemistry-driven optimization of compound 1 from a focused NMT inhibitor library led to the identification of two early lead compounds 4 and 25, which showed good enzyme and cellular potency and excellent selectivity over human NMT. These molecules provide a valuable starting point for further development.
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Oct 2012
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I24-Microfocus Macromolecular Crystallography
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John
Menting
,
Jonathan
Whittaker
,
Mai B.
Margetts
,
Linda J.
Whittaker
,
Geoffrey K.-W.
Kong
,
Brian J.
Smith
,
Christopher J.
Watson
,
Lenka
záková
,
Emília
Kletvíková
,
Jiří
Jiráček
,
Shu Jin
Chan
,
Donald F.
Steiner
,
Guy G.
Dodson
,
Andrzej M.
Brzozowski
,
Michael A.
Weiss
,
Colin W.
Ward
,
Michael C.
Lawrence
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.
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Jan 2013
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I24-Microfocus Macromolecular Crystallography
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Open Access
Abstract: Despite the recent first structural insight into the insulin-insulin receptor complex, the role of the C terminus of the B-chain of insulin in this assembly remains unresolved. Previous studies have suggested that this part of insulin must rearrange to reveal amino acids crucial for interaction with the receptor. The role of the invariant PheB24, one of the key residues of the hormone, in this process remains unclear. For example, the B24 site functionally tolerates substitutions to d-amino acids but not to l-amino acids. Here, we prepared and characterized a series of B24-modified insulin analogues, also determining the structures of [d-HisB24]-insulin and [HisB24]-insulin. The inactive [HisB24]-insulin molecule is remarkably rigid due to a tight accommodation of the l-His side chain in the B24 binding pocket that results in the stronger tethering of B25-B28 residues to the protein core. In contrast, the highly active [d-HisB24]-insulin is more flexible, and the reverse chirality of the B24C? atom swayed the d-HisB24 side chain into the solvent. Furthermore, the pocket vacated by PheB24 is filled by PheB25, which mimics the PheB24 side and main chains. The B25?B24 downshift results in a subsequent downshift of TyrB26 into the B25 site and the departure of B26-B30 residues away from the insulin core. Our data indicate the importance of the aromatic l-amino acid at the B24 site and the structural invariance/integrity of this position for an effective binding of insulin to its receptor. Moreover, they also suggest limited, B25-B30 only, unfolding of the C terminus of the B-chain upon insulin activation.
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Feb 2013
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I02-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[9948]
Open Access
Abstract: The N-terminus of the B-chain of insulin may adopt two alternative conformations designated as the T- and R-states. Despite the recent structural insight into insulin–insulin receptor (IR) complexes, the physiological relevance of the T/R transition is still unclear. Hence, this study focused on the rational design, synthesis, and characterization of human insulin analogues structurally locked in expected R- or T-states. Sites B3, B5, and B8, capable of affecting the conformation of the N-terminus of the B-chain, were subjects of rational substitutions with amino acids with specific allowed and disallowed dihedral φ and ψ main-chain angles. α-Aminoisobutyric acid was systematically incorporated into positions B3, B5, and B8 for stabilization of the R-state, and N-methylalanine and d-proline amino acids were introduced at position B8 for stabilization of the T-state. IR affinities of the analogues were compared and correlated with their T/R transition ability and analyzed against their crystal and nuclear magnetic resonance structures. Our data revealed that (i) the T-like state is indeed important for the folding efficiency of (pro)insulin, (ii) the R-state is most probably incompatible with an active form of insulin, (iii) the R-state cannot be induced or stabilized by a single substitution at a specific site, and (iv) the B1–B8 segment is capable of folding into a variety of low-affinity T-like states. Therefore, we conclude that the active conformation of the N-terminus of the B-chain must be different from the “classical” T-state and that a substantial flexibility of the B1–B8 segment, where GlyB8 plays a key role, is a crucial prerequisite for an efficient insulin–IR interaction.
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Jun 2014
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I02-Macromolecular Crystallography
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Diamond Proposal Number(s):
[7864]
Open Access
Abstract: The structural characterization of the insulin-insulin receptor (IR) interaction still lacks the conformation of the crucial B21-B30 insulin region, which must be different from that in its storage forms to ensure effective receptor binding. Here, it is shown that insulin analogues modified by natural amino acids at the TyrB26 site can represent an active form of this hormone. In particular, [AsnB26]-insulin and [GlyB26]-insulin attain a B26-turn-like conformation that differs from that in all known structures of the native hormone. It also matches the receptor interface, avoiding substantial steric clashes. This indicates that insulin may attain a B26-turn-like conformation upon IR binding. Moreover, there is an unexpected, but significant, binding specificity of the AsnB26 mutant for predominantly the metabolic B isoform of the receptor. As it is correlated with the B26 bend of the B-chain of the hormone, the structures of AsnB26 analogues may provide the first structural insight into the structural origins of differential insulin signalling through insulin receptor A and B isoforms.
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Oct 2014
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I02-Macromolecular Crystallography
I03-Macromolecular Crystallography
I04-Macromolecular Crystallography
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Diamond Proposal Number(s):
[9948]
Abstract: Heparan sulfate (HS) is a glycosaminoglycan that forms a key component of the extracellular matrix (ECM). Breakdown of HS is carried out by heparanase (HPSE), an endo-β-glucuronidase of the glycoside hydrolase 79 (GH79) family. Overexpression of HPSE results in breakdown of extracellular HS and release of stored growth factors and hence is strongly linked to cancer metastasis. Here we present crystal structures of human HPSE at 1.6-Å to 1.9-Å resolution that reveal how an endo-acting binding cleft is exposed by proteolytic activation of latent proHPSE. We used oligosaccharide complexes to map the substrate-binding and sulfate-recognition motifs. These data shed light on the structure and interactions of a key enzyme involved in ECM maintenance and provide a starting point for the design of HPSE inhibitors for use as biochemical tools and anticancer therapeutics.
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Nov 2015
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I03-Macromolecular Crystallography
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Jitka
Viková
,
Michaela
Collinsová
,
Emília
Kletvíková
,
Miloš
Buděšínský
,
Vojtěch
Kaplan
,
Lenka
Žáková
,
Václav
Veverka
,
Rozálie
Hexnerová
,
Roberto J. Tarazona
Aviñó
,
Jana
Straková
,
Irena
Selicharová
,
Václav
Vaněk
,
Daniel W
Wright
,
Christopher J
Watson
,
Johan P
Turkenburg
,
Andrzej M
Brzozowski
,
Jiří
Jiráček
Diamond Proposal Number(s):
[7864]
Open Access
Abstract: Insulin is a key hormone of human metabolism with major therapeutic importance for both types of diabetes. New insulin analogues with more physiological profiles and better glycemic control are needed, especially analogues that preferentially bind to the metabolic B-isoform of insulin receptor (IR-B). Here, we aimed to stabilize and modulate the receptor-compatible conformation of insulin by covalent intra-chain crosslinking within its B22–B30 segment, using the CuI-catalyzed Huisgen 1,3-dipolar cycloaddition reaction of azides and alkynes. This approach resulted in 14 new, systematically crosslinked insulin analogues whose structures and functions were extensively characterized and correlated. One of the analogues, containing a B26–B29 triazole bridge, was highly active in binding to both IR isoforms, with a significant preference for IR-B. Our results demonstrate the potential of chemistry-driven modulation of insulin function, also shedding new light on the functional importance of hormone’s B-chain C-terminus for its IR-B specificity.
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Jan 2016
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