Biomedical subjects

A Coda

Publications and source records attributed to A Coda.

At least 37 records · Page 2Linked to original sources

PubMed1997

[Stoppa's intervention. The complications nd results].

The authors report their experience with the giant prosthetic reinforcement of the visceral sac (Stoppa procedure), developed in the last 6 years operating 126 cases. Postoperative period was regular for two third of the patients, but only in 4 cases we can consider complication severe: 2 cases of preperitoneal haemorrhage with haematoma formation and subsequent recurrence; one sepsis of the preperitoneal space around the prosthesis, cured with drainage and conservative measures without recurrence, and then one peritonitis in a morbid obese individual. There was no mortality. 93.3% of the patients has been clinically controlled after over 6 months (average 27 months; range 6-67 months): 8 recurrences have been observed (3.6% of the hernias operated). 7 required reintervention. Therefore it is possible to affirm that 91% of the operated patients had good results.

Adult↗

PubMed1996

Crystal structure of NH3-dependent NAD+ synthetase from Bacillus subtilis.

NAD+ synthetase catalyzes the last step in the biosynthesis of nicotinamide adenine dinucleotide. The three-dimensional structure of NH3-dependent NAD+ synthetase from Bacillus subtilis, in its free form and in complex with ATP, has been solved by X-ray crystallography (at 2.6 and 2.0 angstroms resolution, respectively) using a combination of multiple isomorphous replacement and density modification techniques. The enzyme consists of a tight homodimer with alpha/beta subunit topology. The catalytic site is located at the parallel beta-sheet topological switch point, where one AMP molecule, one pyrophosphate and one Mg2+ ion are observed. Residue Ser46, part of the neighboring 'P-loop', is hydrogen bonded to the pyrophosphate group, and may play a role in promoting the adenylation of deamido-NAD+ during the first step of the catalyzed reaction. The deamido-NAD+ binding site, located at the subunit interface, is occupied by one ATP molecule, pointing towards the catalytic center. A conserved structural fingerprint of the catalytic site, comprising Ser46, is very reminiscent of a related protein region observed in glutamine-dependent GMP synthetase, supporting the hypothesis that NAD+ synthetase belongs to the newly discovered family of 'N-type' ATP pyrophosphatases.

Amide Synthases↗

PubMed1996

Crystal structure of D-amino acid oxidase: a case of active site mirror-image convergent evolution with flavocytochrome b2.

D-amino acid oxidase is the prototype of the FAD-dependent oxidases. It catalyses the oxidation of D-amino acids to the corresponding alpha-ketoacids. The reducing equivalents are transferred to molecular oxygen with production of hydrogen peroxide. We have solved the crystal structure of the complex of D-amino acid oxidase with benzoate, a competitive inhibitor of the substrate, by single isomorphous replacement and eightfold averaging. Each monomer is formed by two domains with an overall topology similar to that of p-hydroxybenzoate hydroxylase. The benzoate molecule lays parallel to the flavin ring and is held in position by a salt bridge with Arg-283. Analysis of the active site shows that no side chains are properly positioned to act as the postulated base required for the catalytic carboanion mechanism. On the contrary, the benzoate binding mode suggests a direct transfer of the substrate alpha-hydrogen to the flavin during the enzyme reductive half-reaction. The active site Of D-amino acid oxidase exhibits a striking similarity with that of flavocytochrome b2, a structurally unrelated FMN-dependent flavoenzyme. The active site groups (if these two enzymes are in fact superimposable once the mirror-image of the flavocytochrome b2 active site is generated with respect to the flavin plane. Therefore, the catalytic sites of D-amino acid oxidase and flavocytochrome b2 appear to have converged to a highly similar but enantiomeric architecture in order to catalvze similar reactions (oxidation of alpha-amino acids or alpha-hydroxy acids), although with opposite stereochemistry.

4-Hydroxybenzoate-3-Monooxygenase↗

PubMed1996

Structural bases for sulfide recognition in Lucina pectinata hemoglobin I.

The X-ray crystal structure of the sulfide derivative of ferric Lucina pectinata hemoglobin component I (HbI) has been determined at 1.9 A resolution (R-factor 0.186). The heme pocket structural organization of HbI is in keeping with its ligand binding properties. The fast sulfide association rate constant can be related to the presence of Gln(64)E7, as the heme distal residue, together with the protein structural properties in the CD-E distal region. Moreover, the very high sulfide affinity for HbI is reflected by the exceptionally slow ligand dissociation rate. The stabilization of the heme-bound sulfide molecule is achieved through hydrogen bonding to Gln(64)E7, as well as by finely tuned aromatic-electrostatic interactions with the clustered residues Phe(29)B10, Phe(43)CD1 and Phe(68)E11. Such a peculiar arrangement of phenylalanyl residues at the distal ligand binding site has not been observed before in the globin family, and is unique to HbI, a protein functionally devoted to sulfide transport.

Animals↗

PubMed1996

Three-dimensional structure of Xenopus laevis Cu,Zn superoxide dismutase b determined by X-ray crystallography at 1.5 A resolution.

Xenopus laevis Cu,Zn superoxide dismutase (recombinant isoenzyme b) has been crystallized and the structure determined at 1.49 A resolution. The crystals belong to space group P2(1)2(1)2(1), with cell constants a = 73.33, b = 68.86, c = 59.73 A, and contain one dimeric molecule of M(r) 32 000 per asymmetric unit. The structure was solved by molecular-replacement techniques using the semisynthetic Cu,Co bovine enzyme as search model, and refined by molecular dynamics with a crystallographic pseudo-energy term. During the final steps, positional and anisotropic thermal parameters of the atoms were refined. The R factor for the 49 209 unique reflections in the 10.0-1.49 A resolution range is 0.104, for a model comprising 2023 protein atoms, two Cu(2+), two Zn(2+), and 353 water molecules. The overall temperature factor for the model, including solvent, is 20.3 A(2), while the calculated r.m.s. coordinate error for the refined model is 0.036 A. As suggested by the primary structure homology to any other known intracellular eukaryotic superoxide dismutase (> 50%), the typical structural scaffolding of flattened antiparallel eight-stranded (beta-barrel is well conserved in X. laevis Cu,Zn superoxide dismutase b, together with the coordination geometry of the metal centers in the active site. The higher thermal stability of the bb X. laevis superoxide dismutase homodimer, with respect to dimers involving the a-type isoenzyme subunit(s), can be related, on the basis of the high-resolution structure, to side-chain and solvent interactions centered on residue Tyr149, in both b-type subunits. The analysis of the overall solvent structure reveals a number of equivalent water molecule sites in the two subunits, and in homologous superoxide dismutase models. Their locations are discussed in detail and classified on the basis of their structural role.

Journal Article↗

PubMed1996

Crystallization of NAD+ synthetase from Bacillus subtilis.

NAD(+)-synthetase is a ubiquitous enzyme catalyzing the last step in the biosynthesis of NAD+. Mutants of NAD+ synthetase with impaired cellular functions have been isolated, indicating a key role for this enzyme in cellular metabolism. Crystals of the enzyme from Bacillus subtilis suitable for x-ray crystallographic investigation have been grown from polyethylene glycol solutions. Investigation on the structural organization of NAD+ synthetase, an enzyme fundamental for NAD+ biosynthesis, and belonging to the recently characterized amidotransferase enzymatic family, will provide more insight into the catalytic mechanism of deamido-NAD+-->NAD+ conversion, a biosynthetic process that is a potential target for the development of antibiotic compounds against Bacillus sp. and related bacteria.

Amide Synthases↗

PubMed1995

Crystallization and preliminary X-ray analysis of pyruvate kinase type I from Escherichia coli.

Crystals of the fructose-l,6-bisphosphate-dependent pyruvate kinase from Escherichia coli have been grown using the hanging-drop vapour-diffusion technique. The space group was found to be C222(1) with cell dimensions a = 76.8, b = 247.5, c = 132.6 A. Diffraction data to 3.0 A resolution have been recorded and the enzyme molecular symmetry analysed through inspection of the self-rotation function. The crystallized protein is in the allosterically inactive T state.

Journal Article↗

PubMed1995

Crystal structure of Escherichia coli pyruvate kinase type I: molecular basis of the allosteric transition.

BACKGROUND: Pyruvate kinase (PK) plays a major role in the regulation of glycolysis. Its catalytic activity is controlled by the substrate phosphoenolpyruvate and by one or more allosteric effectors. The crystal structures of the non-allosteric PKs from cat and rabbit muscle are known. We have determined the three-dimensional structure of the allosteric type I PK from Escherichia coli, in order to study the mechanism of allosteric regulation. RESULTS: The 2.5 A resolution crystal structure of the unligated type I PK in the inactive T-state shows that each subunit of the homotetrameric enzyme comprises a (beta/alpha)8-barrel domain, a flexible beta-barrel domain and a C-terminal domain. The allosteric and active sites are located at the domain interfaces. Comparison of the T-state E. coli PK with the non-allosteric muscle enzyme, which is thought to adopt a conformation similar to the active R-state, reveals differences in the orientations of the beta-barrel and C-terminal domains of each subunit, which are rotated by 17 degrees and 15 degrees, respectively. Moreover, the relative orientation of the four subunits differs by about 16 degrees in the two enzymes. Highly conserved residues at the subunit interfaces couple these movements to conformational changes in the substrate and allosteric effector binding sites. The subunit rotations observed in the T-state PK induce a shift in loop 6 of the (beta/alpha)8-barrel domain, leading to a distortion of the phosphoenolpyruvate-binding site accounting for the low substrate affinity of the T-state enzyme. CONCLUSIONS: Our results suggest that allosteric control of PK is accomplished through remarkable domain and subunit rotations. On transition from the T- to the R-state all 12 domains of the functional tetramer modify their relative orientations. These concerted motions are the molecular basis of the coupling between the active centre and the allosteric site.

Allosteric Regulation↗

PubMed1995

Structure of a complex of two plasma proteins: transthyretin and retinol-binding protein.

The three-dimensional structure of the complex formed by two plasma proteins, transthyretin and retinol-binding protein, was determined from x-ray diffraction data to a nominal resolution of 3.1 angstroms. One tetramer of transthyretin was bound to two molecules of retinol-binding protein. The two retinol-binding protein molecules established molecular interactions with the same transthyretin dimer, and each also made contacts with one of the other two monomers. Thus, the other two potential binding sites in a transthyretin tetramer were blocked. The amino acid residues of the retinol-binding protein that were involved in the contacts were close to the retinol-binding site.

Amino Acid Sequence↗

PubMed1995

Reptile heme protein structure: X-ray crystallographic study of the aquo-met and cyano-met derivatives of the loggerhead sea turtle (Caretta caretta) myoglobin at 2.0 A resolution.

The X-ray crystal structures of the aquo-met and cyano-met derivatives of the loggerhead sea turtle (Caretta caretta) myoglobin have been determined at 2.0 A resolution (R = 0.182, and 0.178, respectively). The results here reported, representing the first reptile globin solved by X-ray crystallography, have been analyzed in parallel with data for related monomeric hemoproteins, and indicate a strong overall structural similarity between the loggerhead sea turtle and mammalian myoglobins, reflected by the 63% amino acid identity of their primary structures. The root-mean-square deviation between the entire polypeptide backbones of loggerhead sea turtle and sperm whale myoglobins, after structure superposition, is 0.83 A. Upon cyanide binding to the protein distal site, the iron-bound water molecule present in the aquo-met form is displaced by the incoming ligand. Cyanide is oriented towards the inner part of the heme distal site forming a Fe-C-N angle of 133 degrees.

Animals↗

PubMed1995

[Extra-pelvic mesonephric cyst].

The authors report a case of parovarian mesonephryc cyst that came out through femoral canal outside the pelvis and appeared in crural region. Briefly its features are discussed and compared to Literature.

Cysts↗

PubMed1994

Structure of the sulfide-reactive hemoglobin from the clam Lucina pectinata. Crystallographic analysis at 1.5 A resolution.

The crystal structure of the aquo-met form of the sulfide-reactive hemoglobin (component I) from the gill of the symbiont-harboring mollusc, Lucina pectinata, has been solved and refined at 1.5 A resolution, based on synchrotron radiation X-ray diffraction data, and employing molecular replacement techniques. The crystallographic R-factor, calculated for the data in the 15.0 to 1.5 A resolution range, is 0.170, with highly regular stereochemical parameters for the protein model, and including 131 water molecules. The monomeric hemoglobin I chain consists of 142 amino acid residues, which have been partly identified on the basis of the crystallographic analysis. The molecule is characterized by an unusual distribution of aromatic residues, particularly in the region surrounding the distal site in the heme pocket. The heme distal residue is Gln(64)E7, while other notable amino acid substitutions include Trp(21)B2, Phe(29)B10, Leu(46)CD3, Phe(68)E11 and Trp(75)E18. An amino acid insertion (Ser44) is observed between sites CD1 and CD2. In the aquo-met protein, a water molecule is present at the sixth coordination position of the heme iron, and hydrogen bonded to Gln(64)E7. Simple model building shows that a dioxygen molecule, bound to ferrous protein, would contact with its free atom the ring edge of Phe(29)B10, being thus stabilized at the coordination site by an aromatic-electrostatic interaction. Similarly, the unique packing and organization of aromatic residues in the surroundings of the heme distal site is proposed as the molecular basis of the very high affinity of Lucina pectinata hemoglobin I for hydrogen sulfide, considered as one of the two physiological ligands of the protein.

Amino Acid Sequence↗

PubMed1994

Crystallization of the macromolecular complex transthyretin-retinol-binding protein.

Single crystals of the macromolecular complex transthyretin-retinol-binding protein have been obtained. Transthyretin is a carrier of the hormone thyroxine in plasma whereas retinol-binding protein is the specific transporter of the alcohol form of vitamin A in the same medium. This macromolecular complex is found under physiological conditions in plasma and is believed to play an important physiological role. The complex can be formed in vitro by proteins purified from different species. Our crystals are grown with chicken retinol-binding protein complexed to human transthyretin. They are grown by equilibrium dialysis versus 2.3 M ammonium sulphate, 3% ethylene glycol buffered with 0.1 M succinate (pH 5.5). Their space group is I222 (or I2(1)2(1)2(1)) with unit cell parameters a = 222.4 A, b = 163.4 A and c = 55.5 A. Using a conventional X-ray source, we have collected a complete data set of the crystals to a nominal resolution of 3.1 A.

Animals↗

PubMed1994

Crystal structure of the cyanide-inhibited Xenopus laevis Cu,Zn superoxide dismutase at 98 K.

The crystal structure of cyanide-inhibited X. laevis Cu,Zn superoxide dismutase has been studied and refined based on diffraction data collected at 98 K. The final R-factor for the 27,299 reflections in the 10.0-1.7 A resolution range is 0.170. The cyanide anion, which is a competitive inhibitor expected to mimic the superoxide binding mode, binds directly to the active site copper atom, replacing the coordinated water molecule. Moreover, the anion establishes a strong electrostatic interaction with the guanidinium group of the conserved active site residue Arg141. The coordination sphere of Cu2+ is partly altered with respect to the uninhibited enzyme: a displacement of 0.41 A in subunit A, and 0.27 A in subunit B of the dimeric enzyme is observed for the Cu2+ ions. Only two ligands in the Cu2+ coordination sphere (His46 and His118) are significantly affected by cyanide binding, whereas virtually no rearrangement of the Zn2+ ligands is reported.

Animals↗

PubMed1994

Crystal structure of apo-avidin from hen egg-white.

The three-dimensional structure of hen egg-white apo-avidin, crystallized in a tetragonal crystal form, has been refined to a crystallographic R-factor of 0.164 (for the 6390 observed reflections in the 10.0 to 2.8 A resolution range). As in the case of holo-avidin, from which starting atomic co-ordinates were derived, the functional tetramer shows 2-pseudo 22 molecular symmetry. Each promoter is organized in an eight-stranded antiparallel orthogonal beta-barrel, with extended loop regions, which define the biotin binding pocket in the protomer core. In the absence of biotin the binding site is only partly occupied by water molecules. The structure of the binding site residues, as observed in apo-avidin, is highly complementary to that of the incoming biotin molecule, accounting for prompt and specific recognition. A crystal lattice contact may play a role in stabilizing the conformation of one protein loop, part of the biotin-binding pocket.

Amino Acid Sequence↗

PubMed1994

[Hemorrhagic pseudocyst of the spleen].

The authors report a rare case of haemorrhagic pseudocyst of the spleen in a 37 years old female who had always enjoyed very good health and who didn't remember any previous chest or abdominal traumas. Due to the initial refusal of the patient to undergo splenectomy, it has been possible to follow pathology progress. An echography of the cyst 6 months later, showed a maximum diameter increase of more than 2 cm and a further thinning of the cyst wall. Afterwards the patient decided to undergo the operation. The spleen showed a hollow of 10 cm of maximum diameter, with a degraded haematic content; the final histological examination confirmed the initial diagnosis of haemorrhagic pseudocyst of the spleen.

Adult↗

PubMed1993

X-ray crystal structure of ferric Aplysia limacina myoglobin in different liganded states.

The X-ray crystal structure of the ligand-free ferric form of Aplysia limacina myoglobin (pH 6.0) has been refined at 1.7 A resolution (R = 15.1%), and its cyanide, thiocyanate and imidazole derivatives studied by difference Fourier techniques at atomic resolution. The crystallographic R-factors of the three different derivatives reported are 16.1%, 16.1% and 15.6% at 1.8 A, 2.0 A and 2.0 A resolution, respectively. The present results have been analyzed in parallel with previous crystallographic studies on the molecular structures of the fluoride and azide derivatives of ferric Aplysia limacina myoglobin. Ligand binding to the distal site of the heme pocket results in different networks of hydrogen bonds involving to various degrees the bound ligand, residue Arg(66)E10, the heme propionate III, ordered water molecules and/or protein backbone atoms from the CD region. In particular, Arg(66)E10 stabilizes the bound ligand and compensates for the absence of the hydrogen bond donor residue HisE7, commonly present in oxygen-carrying globins.

Animals↗

PubMed1993

Crystallisation and preliminary crystallographic analysis of recombinant Xenopus laevis Cu,Zn superoxide dismutase b.

The recombinant Cu,Zn superoxide dismutase from the South African frog Xenopus laevis, expressed in E. coli, has been crystallized in a form suitable for high resolution crystallographic investigations. The crystals grow from polyethylene glycol solutions, at pH 6.0, 28 degrees C, and belong to the orthorhombic space group P2(1)2(1)2(1) with unit cell edges a = 73.33, b = 68.86, c = 59.73 A, one protein dimer (32,000 M(r)) per asymmetric unit. Diffraction data have been collected to 3.0 A resolution, and a molecular replacement solution found for Xenopus laevis superoxide dismutase using the bovine enzyme as search model. The crystallographic R-factor corresponding to this solution is 0.412, in the 15.0-3.0 A resolution range.

Animals↗