Biomedical subjects

C Cambillau

Publications and source records attributed to C Cambillau.

At least 109 records · Page 6Linked to original sources

PubMed1992

X-ray structure of a biantennary octasaccharide-lectin complex refined at 2.3-A resolution.

The structure and flexibility of saccharides have a profound and specific influence in several biological processes such as protein protection and the maintenance of conformational integrity, and in recognition events involving viruses, enzymes, and lectins. To establish the structural bases of these phenomena, we describe herein the extensively refined 2.3-A resolution x-ray structure of a biantennary octasaccharide of the N-acetyllactosamine type, complexed to isolectin I from Lathyrus ochrus. The two octasaccharides are located in clefts at each end of the long axis of the lectin. The conformations of both the lectin and the saccharide are slightly modified upon binding. The complex is stabilized by numerous hydrogen bonds, many of them involving water molecules. It is also stabilized by van der Waals interactions, including some with aromatic residues. A more general model of a possible lectin-glycoprotein interaction is also proposed.

Binding Sites↗

PubMed1992

Stimulation of rat pancreatic tumoral AR4-2J cell proliferation by pituitary adenylate cyclase-activating peptide.

In the present work the effects of the novel neuropeptide Pituitary Adenylate Cyclase Activating Peptide (PACAP) on both AR4-2J cell growth and the modulation of ornithine decarboxylase activity were investigated. Both PACAP38 and the amidated form PACAP27 caused a concentration-dependent stimulation of AR4-2J cell growth; the maximal increase was seen at 1 nmol/L (30% above control, P less than 0.01) with a half-maximal effect at 0.01 nmol/L. Ornithine decarboxylase activity was also increased by PACAP in a dose-dependent manner, reaching half-maximal stimulation at 0.5 nmol/L. The addition of 1 nmol/L of somatostatin analog SMS 201-995 totally suppressed PACAP-stimulated AR4-2J cell growth. Vasoactive intestinal polypeptide (3 mumol/L) and 8-bromo-cyclic adenosine monophosphate (1 mmol/L) had no effect on cell proliferation. Treatment of cells by pertussis toxin (25 ng.mL-1.day-1) suppressed PACAP-stimulated AR4-2J cell growth but enhanced PACAP-induced stimulation of adenylate cyclase activity. It was concluded that PACAP stimulates AR4-2J cell proliferation by a mechanism that seems independent of cyclic adenosine monophosphate production. The mitogenic effect of PACAP depends on a pertussis toxin-sensitive G protein and is associated with an increase of ornithine decarboxylase activity.

Adenylate Cyclase Toxin↗

PubMed1992

Characterization of a membrane tyrosine phosphatase in AR42J cells: regulation by somatostatin.

A phosphotyrosyl protein phosphatase (PTPase) activity has been characterized in the plasma membranes of confluent AR42J pancreatic tumor cells using 32P-labeled poly(Glu, Tyr) as substrate. Membrane PTPase activity exhibited an apparent Michaelis constant of 3 microM and an apparent maximal velocity of 0.9 nmol.min-1.mg-1. It was inhibited by orthovanadate, zinc, poly(Glu,Tyr) and was stimulated by EDTA and dithiothreitol. Gel filtration of solubilized plasma membranes gave a peak of enzyme activity at a relative molecular weight of 70,000. Plasma membrane PTPase activity was changed during AR42J cell growth. At the beginning of culture, the control PTPase activity was minimal. Over the 5 days of culture, PTPase activity increased to reach a maximum (3.5-fold over control activity) preceding confluency by 2 days. Then the high level of PTPase activity was sustained until confluency. Incubation of the cells with the stable somatostatin analogue SMS 201-995 (SMS) resulted in a rapid and transient activation of crude membrane PTPase activity. Activation reached a maximum level within 5 min of addition and return to control levels within 20 min. The effect of SMS was dose dependent with half-maximal and maximal activation occurring at 6 pM and 0.1 nM SMS respectively.

Animals↗

PubMed1991

Effects of gene mutations in lipoprotein and hepatic lipases as interpreted by a molecular model of the pancreatic triglyceride lipase.

A molecular model of human pancreatic lipase (Winkler, F. K., D'Arcy, A., and Hunziker, W. (1990) Nature 343, 771-774) is used to explain the possible structural effects of the amino acid mutations identified to date in the human lipoprotein and hepatic lipase genes. A sequence homology profile was used to evaluate the alignment of the amino acid sequences of all three lipolytic enzymes (Kirchgessner, T. G., Chuat, J.-C., Heinzmann, C., Etienne, J., Guilhot, S., Svenson, K., Ameis, D., Pilon, C., D'Auriol, L., Andalibi, A., Schotz, M. C., Galibert, F., and Lusis, A. J. (1989) Proc. Natl. Acad. Sci. U. S. A. 86, 9647-9651) with respect to the secondary structure elements identified in the pancreatic lipase. As expected, maximum homology is observed in internal regions namely the hydrophobic strands of the central beta-pleated sheet. This observation strongly supports the hypothesis that all three molecules exhibit a very similar three-dimensional structure, particularly in the N-terminal catalytic domain. There is considerable variation in some of the surface loops connecting the individual strands, whereas others are conserved. It is hypothesized that the most conserved loops located around the active site are responsible for the catalytic function (similar for all three enzymes), whereas those that markedly differ are involved in the regulation at the molecular level, namely the binding of colipase (pancreatic enzyme) and apolipoprotein CII (lipoprotein lipase). The currently available library of hepatic and lipoprotein gene mutations seems to indicate that the majority of mutants disrupt the folding of the polypeptide chain, rather than affect specific constellations in and around the catalytic site or regulatory loops.

Amino Acid Sequence↗

PubMed1991

Systematic use of the incomplete factorial approach in the design of protein crystallization experiments.

We have used the Incomplete Factorial Approach (Carter, C. W., and Carter, C. W., Jr. (1979) J. Biol. Chem. 254, 12219-12223) in conjunction with the program Cristal (Roussel, A., Serre, L., Frey M., and Fontecilla-Camps, J. (1990) J. Crystal Growth 106, 405-409) to crystallize six different proteins. We were able to obtain crystals and to identify the critical factors for crystallization for each of these six proteins. In some of the cases, we succeeded on the first try while using only minute amounts of protein. This study proves that the Incomplete Factorial Approach is a powerful tool in identifying the factors that need to be varied to achieve crystallization. Single crystals of adequate size were obtained for all the proteins reported here, although some did not diffract well enough to be studied by x-ray diffraction methods; the asymmetric units of these latter crystals contain a large metric units of these latter crystals contain a large number of molecules, which is most likely due to the presence of significant amounts of carbohydrate in the proteins.

Animals↗

PubMed1991

Data bank of three-dimensional structures of disaccharides: Part II, N-acetyllactosaminic type N-glycans. Comparison with the crystal structure of a biantennary octasaccharide.

Conformational energy maps and descriptions of structures at the local minima are presented for the following fragments found in N-acetyllactosaminic type glycans of N-glycoproteins: GlcNAc beta(1-2)Man, GlcNAc beta(1-4)Man, GlcNAc beta(1-6)Man, Gal beta(1-4)GlcNAc, GlcNAc beta(1-3)Gal, Fuc alpha(1-6)GlcNAc, Fuc alpha(1-3)GlcNAc, Xyl beta(1-2)Man, Gal beta(1-3)GlcNAc and GlcNAc beta(1-6)Gal. These results are the second part of a data bank on glycoprotein moieties; five disaccharides found in oligomannose type N-glycans were analysed earlier (Imberty et al., 1990, Glycoconjugate J 7:27-54). In the present study, three to seven minima are found for each dimer. Conformations of disaccharide fragments found in the crystal structure of the complex of a biantennary octasaccharide with Lathyrus ochrus lectin are plotted on these energy maps. While the observed conformations are at predicted minima, they are not always at the minimum predicted to have the lowest energy. Further, not all observed conformations are stabilized by the exo-anomeric effect. We conclude that these oligosaccharides are highly flexible.

Carbohydrate Conformation↗

PubMed1991

Monoclonal antibody 117,C-11 recognizes three exposed regions on the surface of the Lathyrus ochrus isolectin I.

A mouse IgA monoclonal antibody, MoAb 117,C-11, was produced against the glucose/mannose specific isolectin I (LoLI) from Lathyrus ochrus seeds, a legume two-chain lectin comprising two heavy subunits non covalently associated to two light subunits. The MoAb reacted in ELISA with three different peptides representing three distinct amino acid stretches present on the surface of the heavy subunits of LoLI. Since these three stretches are too far apart to build a discontinuous/conformational epitope, it is presumed that they act as continuous/sequential epitopes. The presence of a complete or partial TGNV sequence within these epitopes could account for their reactivity towards the MoAb, as shown by inhibition studies using a chemically synthesized TGNV peptide. MoAb 117,C-11 also reacted with closely related two-chain lectins.

Amino Acid Sequence↗

PubMed1990

X-ray structure of a (alpha-Man(1-3)beta-Man(1-4)GlcNAc)-lectin complex at 2.1-A resolution. The role of water in sugar-lectin interaction.

We describe herein the high resolution refined x-ray structure of a trisaccharide, which is a part of the N-acetyllactosamine type glycan found in the majority of the N-glycosyl-proteins, complexed to the isolectin I. According to the potentials used by Imberty et al. (Imburty, A., Gerber, S., Tran, V., and Pérez, S. (1990) Glycoconjugate J. 7, 27-54) the trisaccharide is in a low-energy state. Only one mannose moiety establishes direct hydrogen bonds with the lectin, as it is the case for monosaccharide-lectin complexes. The comparison of our trisaccharide with the one determined in solution by Warin et al. (Warin, V., Baert, F., Fouret, R., Strecker, G., Fournet, B., and Montreuil, J. (1979) Carbohydr. Res. 76, 11-22) shows that both adopt roughly the same conformation. The differences in these two sugar structures allow us to assign the role of water molecules present in the vicinity of our trisaccharide for the stabilization of this sugar-lectin complex.

Carbohydrate Sequence↗

PubMed1990

Crystallization and preliminary X-ray study of a recombinant cutinase from Fusarium solani pisi.

Recombinant cutinase from Fusarium solani pisi is expressed and excreted with very high yields in Escherichia coli cultures. Cutinase was crystallized at 20 degrees C using the vapour diffusion technique, with polyethylene glycol 6000 as precipitant. Best crystals were obtained at pH 7.0 with polyethylene glycol 6000 as precipitant. Best crystals were obtained at pH 7.0 with polyethylene glycol at 15 to 20%. They are monoclinic, with space group P2(1) and cell dimensions a = 35.1 A, b = 67.4 A, c = 37.05 A and beta = 94.0 degrees; they diffract beyond 1.5 A resolution. The asymmetric unit contains one molecule of 22,000 Da (Vm = 1.98 A3/Da; 38% water).

Carboxylic Ester Hydrolases↗

PubMed1990

X-ray crystal structure determination and refinement at 1.9 A resolution of isolectin I from the seeds of Lathyrus ochrus.

Orthorhombic crystals of isolectin I (LOLI) from the seeds of Lathyrus ochrus were first obtained during the STS 29 space shuttle mission. Subsequently, isostructural crystals were also obtained in the laboratory. They belong to the space group P2(1)2(1)2, with cell dimensions a = 135.84 A, b = 63.12 A and c = 54.54 A with one functional entity, a dimer, in the asymmetric unit (Vm = 2.2 A3/Da). The three-dimensional structure of LOLI, which was solved by the molecular replacement method using a 3 A resolution model of pea lectin, has subsequently been refined by using crystallographic data between 8.0 A and 1.9 A resolution, coupled to molecular dynamics and energy minimization techniques. The conventional R-factor is 0.185 for Fo greater than 1 sigma(Fo). The final model includes 220 well-defined water molecules and has root-mean-square deviations from ideal bond distances and angles of 0.004 A and 3 degrees, respectively. Only slight conformation differences have been found between the two alpha beta monomers. The molecular structure of LOLI, the first to be determined from the genus Lathyrus, is very similar to those of concanavalin A, pea lectin and favin. Differences are confined to the loop regions and beta-chain termini. Comparison of equivalent C alpha atom positions between our final model and the pea lectin structure shows slight differences in the association of the two monomers, which are probably due to the different environments in the crystals. The root-mean-square deviation between C alpha atoms of LOLI and pea lectin is 0.40 A. The metal binding sites are very similar in pea lectin, concanavalin A and LOLI. The sugar-binding sites of LOLI are occupied by four well-ordered water molecules each. The cleavage site for one of the monomers is specially well defined in the final electron density map: the amino group of Glul (alpha) seems to form a salt bridge with the carboxylate group of the terminal Asn181 (beta). A detailed analysis of the difference in crystal packing contacts between pea lectin and LOLI shows that, as might be expected, several of the intermolecular interactions are mediated by residues that correspond to substitutions in the LOLI amino acid sequence.

Amino Acid Sequence↗

PubMed1990

Co-crystallization and preliminary X-ray diffraction studies of Lathyrus ochrus isolectin I with di- and trisaccharides, and a biantennary octosaccharide.

Isolectin I (LOL I) isolated from the seeds of Lathyrus ochrus has been crystallized in the presence of four different oligosaccharides from an N-acetyllactosaminic type biantennary glycan of human lactotransferrin. The crystals containing putative complexes of LOL I with two different disaccharides are isostructural with the saccharide-free LOL I form (space group P2(1)2(1)2, a = 135.8 A, b = 63.1 A and c = 54.5 A). The LOL I-trisaccharide complex crystallizes in the same space group with small but significant changes in the cell dimensions: a = 136.9 A,b = 63.4 A and c = 54.6 A. Both crystal forms diffract strongly up to at least 1.8 A resolution. One functional entity, an alpha 2 beta 2 tetramer in the asymmetric unit (Mr = 52,000) give a Vm of 2.2 A3/dalton, or a solvent content of approximately 44%. The putative LOL I-octosaccharide complex crystallizes in the monoclinic space group C2 with cell dimensions a = 78.3 A, b = 75.4 A, c = 103.9 A and beta = 92 degrees. The crystals diffract to a resolution of 2.3 A and are suitable for crystallographic investigations. An alpha 2 beta 2 tetramer complexed to two octosaccharides (Mr = 55,000) in the asymmetric unit leads to a Vm value of 2.8 A3/dalton (57% solvent).

Carbohydrate Sequence↗

PubMed1990

Solubilization and characterization of active somatostatin receptors from rat pancreas.

Somatostatin receptors were solubilized from rat pancreatic membranes with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonic acid (CHAPS). The binding of an iodinated somatostatin analog [125I-Tyr3]SMS to the soluble fraction was time-dependent, saturable, and reversible. Scatchard analysis of equilibrium binding data indicated that the soluble extract contained a single class of somatostatin binding sites with a Kd of 0.3 nM and a Bmax of 210 fmol/mg. As observed with membrane-bound receptors, soluble binding receptors were sensitive to the GTP analog GTP gamma S indicating that they are functionally linked to a G protein. A molecular weight of about 400,000 was determined for soluble receptors under native conditions by gel filtration. In denaturing gel electrophoresis, photoaffinity labeling of soluble receptors identified a major protein of Mr = 100,000 and two minor proteins of Mr = 56,000 and 21,000. Isoelectric focusing of soluble receptors revealed that the somatostatin receptor is an acidic protein with pI 4.8. The soluble somatostatin receptor is a glycoprotein which can be specifically bound to the wheat germ agglutinin lectin and eluted by triacetyl-chitotriose.

Animals↗

PubMed1990

Three-dimensional structures of complexes of Lathyrus ochrus isolectin I with glucose and mannose: fine specificity of the monosaccharide-binding site.

The structure of the methyl-alpha-D-mannopyranoside-LOL I complex has been solved by the molecular replacement method using the refined saccharide-free LOL I coordinates as starting model. The methyl-alpha-D-mannopyranoside-LOL I complex was refined by simulated annealing using the program X-PLOR. The final R-factor value is 0.182 [Fo greater than 1 sigma(Fo)]. The isostructural methyl-alpha-D-glucopyranoside-LOL I complex was refined by X-Ray coupled energy minimization using the methyl-alpha-D-mannopyranoside-LOL I structure as a starting model to an R factor of 0.179 (all data). In both crystal forms, each dimer binds two molecules of sugar in pockets found near the calcium ions. The two saccharide moieties, which are in the C1 chair conformation, establish the same hydrogen bond pattern with the lectin. However, the van der Waals contacts are different between the O2, C2, C6, and O6 atoms of the two molecules and the backbone atoms of residues 208-211. Mannose, due to its axial C2 conformation, encloses the backbone atoms of the protein in a clamplike way. Van der Waals energy calculations suggest that this better complementarity of the mannoside molecule with the lectin could explain its higher affinity for isolectin I.

Binding Sites↗

PubMed1990

CRYStallize: a crystallographic symmetry display and handling subpackage in TOM/FRODO.

We have implemented in TOM/FRODO a protein crystallographic symmetry display and handling package, called CRYStallize. This package is designed as an aid in solving protein structures by molecular replacement methods. It allows the rotation/translation solutions provided by molecular replacement programs to be checked in a fast and easy way. Using CRYStallize, approximate solutions can also be improved by manual modifications. Symmetry-related objects, represented as surfaces, can be generated and handled in the same way as the reference molecules, thus permitting an efficient analysis of crystal packing and site accessibility. This program is available in the TOM/FRODO software release, which runs on the Silicon-Graphics workstations.

Computer Graphics↗

PubMed1989

Crystallization and preliminary X-ray study of horse pancreatic lipase.

Horse (Equus caballus) pancreatic lipase (EC 3.1.1.3) has been crystallized using the hanging drop method of vapour diffusion at 20 degrees C. The best crystals were grown from an 8 mg/ml solution in 10 to 20% (w/v) polyethylene glycol 8000, 10 mM-MgCl2, 0.1 M-NaCl, 0.1 M-Mes buffer (pH 5.6). They reach dimensions of 0.8 mm x 0.4 mm x 0.6 mm. X-ray examination of the lipase crystals shows that they are orthorombic with a space group P2(1)2(1)2(1). Their cell dimensions are a = 79.8 A, b = 97.2 A c = 145.3 A. Two molecules per asymmetric unit give a Vm value of 2.82 A3/dalton (56% water content). Lipase crystals strongly diffract to at least 1.8 A resolution. Some molecular properties of horse lipase compared to those of the better-known porcine enzyme are also presented.

Animals↗

PubMed1989

Interactions of rutaecarpine alkaloids with specific binding sites for 2,3,7,8-tetrachlorodibenzo-p-dioxin in rat liver.

Rutaecarpine alkaloids have the capacity to inhibit specific 2,3,7,8-[1,6-3H]tetrachlorodibenzo-p-dioxin (TCDD) binding in rat liver cytosol, as analysed by electrofocusing in polyacrylamide gel. The IC50 value for binding of 7,8-dehydrorutaecarpine was estimated to approximately 7 nM indicating a high-affinity interaction, whereas rutaecarpine appeared less active (IC50 approximately 110 nM). These findings are of interest in view of the fact that analogues to these compounds may be formed following UV-irradiation of tryptophan and that such photo-products have been suggested to constitute (the) endogenous ligand(s) for the TCDD receptor. As further support of this notion, the rutaecarpine alkaloids investigated could be fitted into a rectangle of 6.8 x 13.7 A, a characteristic common for most high affinity ligands of the TCDD receptor hitherto studied. In view of their structural similarity to dehydrorutaecarpine and the agreement of their mol. wt with that of the photoproduct with the highest affinity for the TCDD receptor, we suggest deaza-analogues of dehydrorutaecarpine to represent possible candidates for the endogenous TCDD receptor ligand.

Alkaloids↗

PubMed1989

Direct inhibitory effects of a somatostatin analog, SMS 201-995, on AR4-2J cell proliferation via pertussis toxin-sensitive guanosine triphosphate-binding protein-independent mechanism.

Somatostatin has been demonstrated to negatively regulate pancreatic growth in vivo. In this study we used the AR4-2J rat pancreatic acinar tumor cell line to investigate the effect of a stable somatostatin analog, SMS 201-995 (SMS) on cell proliferation. SMS induced an antiproliferative effect on both serum or epidermal growth factor (EGF)-induced cell proliferation; exposure of the cells for 48 h to SMS caused a slight inhibition of serum-induced proliferation (maximal inhibition, 26%) and abolished the growth-promoting effect of EGF. Maximal effect was observed with 10 nM SMS, and half-maximal (IC50) effect with 0.06-0.1 nM SMS. Binding studies with an iodinated derivative of SMS, [125I-Tyr3]SMS, revealed the presence of a single class of high affinity binding sites on AR4-2J plasma membranes with an equilibrium dissociation constant of 0.2 +/- 0.03 nM and a binding site number of 1.1 +/- 0.07 pmol/mg protein. Addition of the nonhydrolyzable GTP analog, guanosine 5-[gamma-thio] triphosphate (GTP gamma S), increased the rate of dissociation of the specifically bound peptide in agreement with the coupling of somatostatin receptors with a GTP-binding regulatory protein. The good agreement between the IC50 for SMS inhibition of cell proliferation and the apparent Kd for binding indicates that the characterized binding sites are the somatostatin receptors that mediate the antiproliferative effect of SMS. When cells were grown in serum-free medium EGF stimulated AR4-2J cell proliferation with half-maximal (ED50) and maximal effects at 0.6 and 10 nM EGF, respectively. This stimulatory effect of EGF was mediated by specific receptors, since binding studies with [125I]EGF indicated that AR4-2J cells contained a single class of EGF receptors (13,000 sites/cell), with an affinity constant for [125I]EGF (Kd = 0.9 +/- 0.09 nM) close to the ED50 for EGF stimulation of cell growth. To examine if SMS-induced growth inhibition involved a cAMP-dependent mechanism we first studied the effect of SMS on cAMP production. SMS had no effect on basal cAMP, but completely inhibited VIP-stimulated cAMP production with an IC50 of 0.2 nM. Pertussis toxin, which is known to abolish the inhibitory effect of somatostatin on adenylate cyclase activity in AR4-2J cells, did not reverse the ability of SMS to inhibit cell proliferation as well as EGF-induced cell proliferation. These data indicate that the antiproliferative effect of SMS does not involve the GTP-binding protein-mediated negative coupling of somatostatin receptors to adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenylate Cyclase Toxin↗

PubMed1988

Crystallization and preliminary X-ray studies of two isolectins from the seeds of Lathyrus ochrus.

Two isolectins from the seeds of Lathyrus ochrus, LOL I and LOL II, which specifically bind N-acetyllactosamine, have been crystallized using the hanging-drop method and the interface diffusion method, respectively. In the case of LOL I, 2-methylpentane-2,4-diol, polyethylene-glycol 400 or ammonium sulphate have been used as precipitating agents. The best crystals of LOL I were grown at room temperature from a solution of 40% (v/v) methylpentane diol, 50 mM-Hepes at pH 7.5. LOL II crystals have been grown at room temperature from a solution of 32% (v/v) methylpentane diol, 50 mM-2-(N-morpholino)-ethanesulphonic acid at pH 5.5. X-ray examination of the LOL I and LOL II crystals shows that both are monoclinic, space group P2(1). Their cell dimensions are: LOL I, a = 56.4 A, b = 138.8 A, c = 62.9 A, beta = 91 degrees; and LOL II, a = 54.8 A, b = 71.4 A, c = 105.5 A, beta = 105 degrees. Density measurements of the crystals of LOL I indicate that there are two molecules per asymetric unit (Vm = 2.07 A3/dalton). LOL I crystals diffract strongly up to at least 1.8 resolution. Putative crystals of complexes of LOL I with various glycosides were obtained through co-crystallization under the conditions used for the native protein.

Crystallization↗