| 1. |
- Ambort, Daniel, 1978, et al.
(författare)
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Function of the CysD domain of the gel-forming MUC2 mucin.
- 2011
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Ingår i: Biochem Journal. ; 436, s. 61-70
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Tidskriftsartikel (refereegranskat)abstract
- The colonic human MUC2 mucin forms a polymeric gel by covalent disulfide bonds in its N- and C-termini. The middle part of MUC2 is largely composed of two highly O-glycosylated mucin domains that are interrupted by a CysD domain of unknown function. We studied its function as recombinant proteins fused to a removable immunoglobulin Fc domain. Analysis of affinity-purified fusion proteins by native gel electrophoresis and gel filtration showed that they formed oligomeric complexes. Analysis of the individual isolated CysD parts showed that they formed dimers both when flanked by two MUC2 tandem repeats and without these. Cleavages of the two non-reduced CysD fusion proteins and analysis by MS revealed the localization of all five CysD disulfide bonds and that the predicted C-mannosylated site was not glycosylated. All disulfide bonds were within individual peptides showing that the domain was stabilized by intramolecular disulfide bonds and that CysD dimers were of non-covalent nature. These observations suggest that CysD domains act as non-covalent cross-links in the MUC2 gel, thereby determining the pore sizes of the mucus.
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| 2. |
- Grahn, Elin, et al.
(författare)
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Crystallization and preliminary X-ray crystallographic studies of a lectin from the mushroom Marasmius oreades
- 2004
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Ingår i: Acta Crystallographica Section D: Biological Crystallography. - 1399-0047 .- 0907-4449. ; 60:11, s. 2038-2039
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Tidskriftsartikel (refereegranskat)abstract
- The Marasmius oreades agglutinin (MOA) recognizes blood group B oligosaccharides. This mushroom lectin belongs to the ricin superfamily and is currently the only lectin known with exclusive specificity for Galα1,3Gal-structures, as occur in the subterminally fucosylated blood group B epitope Galα1,3(Fucα1,2)Galβ1,4GlcNAc (MOA's preferred ligand) or without fucosylation in the xenotransplantation epitope. MOA has been co-crystallized with the linear blood group B trisaccharide Galα1,3Galβ1,4GlcNAc using the hanging-drop vapour-diffusion technique at room temperature. MOA crystals were grown in the presence of ammonium formate and HEPES buffer. A 3.0 Å data set has been collected. Preliminary analysis of the X-ray data is consistent with space group P3 1 or P3 2 and unit-cell parameters a = b = 105, c = 113 Å, with two dimers per asymmetric unit. © 2004 International Union of Crystallography.
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| 3. |
- Holmner, Åsa, et al.
(författare)
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Blood group antigen recognition by Escherichia coli heat-labile enterotoxin
- 2007
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Ingår i: Journal of Molecular Biology. - London : Elsevier BV. - 0022-2836 .- 1089-8638. ; 371:3, s. 754-764
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Tidskriftsartikel (refereegranskat)abstract
- In a number of bacterial infections, such as Helicobacter pylori, Campylobacter jejuni and Vibrio cholerae infections, a correlation between the severity of disease and blood group phenotype of infected individuals has been observed. In the present investigation, we have studied the molecular basis of this effect for enterotoxigenic Escherichia coli (ETEC) infections. ETEC are non-invasive bacteria, which act through second messenger pathways to cause diarrhea. It has been suggested that the major virulence factor of ETEC from human isolates, i.e. the human heat-labile enterotoxin (hLT), recognizes certain blood group epitopes, although the molecular basis of blood group antigen recognition is unknown. The 2.5 angstrom crystal structure of the receptor-binding B-subunit of hLT in complex with the blood group A antigen analog GalNAc alpha 3(Fuc alpha-2)Gal beta 4(Fuc alpha-3)Glc beta provides evidence of a previously unknown binding site in the native toxin. The structure reveals the molecular interactions underlying blood group antigen recognition and suggests how this protein can discriminate between different blood group epitopes. These results support the previously debated role of hLT in the blood group dependence of ETEC infections. Similar observations regarding the closely related cholera toxin in V. cholera infections are also discussed. (c) 2007 Elsevier Ltd. All rights reserved.
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| 4. |
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| 5. |
- Holmner, Åsa, et al.
(författare)
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Crystal Structures Exploring the Origins of the Broader Specificity of Escherichia coli Heat-Labile Enterotoxin Compared to Cholera Toxin.
- 2011
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Ingår i: Journal of molecular biology. - : Elsevier BV. - 1089-8638 .- 0022-2836. ; 406:3, s. 387-402
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Tidskriftsartikel (refereegranskat)abstract
- Cholera toxin (CT) and Escherichia coli heat-labile enterotoxin (LT) are structurally and functionally related and share the same primary receptor, the GM1 ganglioside. Despite their extensive similarities, these two toxins exhibit distinct ligand specificities, with LT being more promiscuous than CT. Here, we have attempted to rationalize the broader binding specificity of LT and the subtle differences between the binding characteristics of LTs from human and porcine origins (mediated by their B subunit pentamers, hLTB and pLTB, respectively). The analysis is based on two crystal structures of pLTB in complexes with the pentasaccharide of its primary ligand, GM1, and with neolactotetraose, the carbohydrate determinant of a typical secondary ligand of LTs, respectively. Important molecular determinants underlying the different binding specificities of LTB and CTB are found to be contributed by Ser95, Tyr18 and Thr4 (or Ser4 of hLTB), which together prestabilize the binding site by positioning Lys91, Glu51 and the adjacent loop region (50-61) containing Ile58 for ligand binding. Glu7 and Ala1 may also play an important role. Many of these residues are closely connected with a recently identified second binding site, and there appears to be cross-talk between the two binding sites. Binding to N-acetyllactosamine-terminated receptors is further augmented by Arg13 (present in pLT and some hLT variants), as previously predicted.
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| 6. |
- Holmner, Åsa, et al.
(författare)
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Novel binding site identified in a hybrid between cholera toxin and heat-labile enterotoxin: 1.9 A crystal structure reveals the details.
- 2004
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Ingår i: Structure (London, England : 1993). - : Elsevier BV. - 0969-2126 .- 1878-4186. ; 12:9, s. 1655-67
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid between the B subunits of cholera toxin and Escherichia coli heat-labile enterotoxin has been described, which exhibits a novel binding specificity to blood group A and B type 2 determinants. In the present investigation, we have determined the crystal structure of this protein hybrid, termed LCTBK, in complex with the blood group A pentasaccharide GalNAcalpha3(Fucalpha2)Galbeta4(Fucalpha3)GlcNAcbeta, confirming not only the novel binding specificity but also a distinct new oligosaccharide binding site. Binding studies revealed that the new specificity can be ascribed to a single mutation (S4N) introduced into the sequence of Escherichia coli heat-labile enterotoxin. At a resolution of 1.9 A, the new binding site is resolved in excellent detail. Main features include a complex network of water molecules, which is well preserved by the parent toxins, and an unexpectedly modest contribution to binding by the critical residue Asn4, which interacts with the ligand only via a single water molecule.
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| 7. |
- Johansson, Tomas, et al.
(författare)
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X-ray structure of domain I of the proton-pumping membrane protein transhydrogenase from Escherichia coli.
- 2005
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Ingår i: Journal of molecular biology. - : Elsevier BV. - 0022-2836 .- 1089-8638. ; 352:2, s. 299-312
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Tidskriftsartikel (refereegranskat)abstract
- The dimeric integral membrane protein nicotinamide nucleotide transhydrogenase is required for cellular regeneration of NADPH in mitochondria and prokaryotes, for detoxification and biosynthesis purposes. Under physiological conditions, transhydrogenase couples the reversible reduction of NADP+ by NADH to an inward proton translocation across the membrane. Here, we present crystal structures of the NAD(H)-binding domain I of transhydrogenase from Escherichia coli, in the absence as well as in the presence of oxidized and reduced substrate. The structures were determined at 1.9-2.0 A resolution. Overall, the structures are highly similar to the crystal structure of a previously published NAD(H)-binding domain, from Rhodospirillum rubrum transhydrogenase. However, this particular domain is unique, since it is covalently connected to the integral-membrane part of transhydrogenase. Comparative studies between the structures of the two species reveal extensively differing surface properties and point to the possible importance of a rigid peptide (PAPP) in the connecting linker for conformational coupling. Further, the kinetic analysis of a deletion mutant, from which the protruding beta-hairpin was removed, indicates that this structural element is important for catalytic activity, but not for domain I:domain III interaction or dimer formation. Taken together, these results have important implications for the enzyme mechanism of the large group of transhydrogenases, including mammalian enzymes, which contain a connecting linker between domains I and II.
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| 8. |
- Krengel, Ute, 1964, et al.
(författare)
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Preliminary X-ray crystallographic analysis of the secreted chorismate mutase from Mycobacterium tuberculosis: A tricky crystallization problem solved
- 2006
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Ingår i: Acta Crystallographica Section F: Structural Biology and Crystallization Communications. - 1744-3091. ; 62:5, s. 441-445
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Tidskriftsartikel (refereegranskat)abstract
- Chorismate mutase catalyzes the conversion of chorismate to prephenate in the biosynthesis of the aromatic amino acids tyrosine and phenylalanine in bacteria, fungi and plants. Here, the crystallization of the unusual secreted chorismate mutase from Mycobacterium tuberculosis (encoded by Rv1885c), a 37.2 kDa dimeric protein belonging to the AroQγ subclass of mutases, is reported. Crystal optimization was non-trivial and is discussed in detail. To obtain crystals of sufficient quality, it was critical to initiate crystallization at higher precipitant concentration and then transfer the drops to lower precipitant concentrations within 5-15 min, in an adaptation of a previously described technique [Saridakis & Chayen (2000), Protein Sci. 9, 755-757]. As a result of the optimization, diffraction improved from 3.5 to 1.3 Å resolution. The crystals belong to space group P21, with unit-cell parameters a = 42.6, b = 72.6, c = 62.0 Å., β = 104.5°. The asymmetric unit contains one biological dimer, with 167 amino acids per protomer. A soak with a transition-state analogue is also described.
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| 9. |
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| 10. |
- Oswald, Christine, et al.
(författare)
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Crystallization and preliminary crystallographic analysis of the NAD(H)-binding domain of Escherichia coli transhydrogenase
- 2004
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Ingår i: Acta Crystallographica Section D: Biological Crystallography. - 1399-0047 .- 0907-4449. ; 60:4, s. 743-745
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Tidskriftsartikel (refereegranskat)abstract
- Transhydrogenase is a proton-pumping membrane protein that is required for the cellular regeneration of NADPH. The NAD(H)-binding domain (domain I) of transhydrogenase from Escherichia coli was crystallized using the hanging-drop vapour-diffusion technique at room temperature. The crystals, which were grown from PEG 4000 and ammonium acetate in citrate buffer, belong to the triclinic space group P1, with unit-cell parameters a = 38.8, b = 66.8, c = 76.4 Å, α = 67.5, β = 80.8, γ = 81.5°. X-ray diffraction data were collected to 1.9 Å resolution using synchrotron radiation. The crystals contain one dimer of transhydrogenase domain I per asymmetric unit. © 2004 International Union of Crystallography. Printed in Denmark - all rights reserved.
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