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At least 397 records · Page 22Linked to original sources
PubMed1999

Strain in protein structures as viewed through nonrotameric side chains: I. their position and interaction.

We studied the relative spatial positioning of nonrotameric side chains with atypical and strained dihedral angles in well-refined protein tertiary structures. The analysis was confined to buried protein cores, which are less error prone to side-chain positioning. More than half of the proteins with two or more nonrotameric residues displayed clusters of two or more (and up to five) nonrotameric residues. The clusters exhibited lower average crystallographic temperature factors compared with isolated nonrotameric residues. Nonrotameric clusters showed significantly tighter packing than corresponding rotameric clusters and had distinct residue compositions that did not correlate with amino acid characteristics such as size, hydrophobicity, turn preference, and the like. Such nonrotameric residue biases would suggest that spatially concentrated strain in protein folds would be minimized by lowered vibrational energy. Furthermore, nonrotameric residues avoided helices and strands and mostly preferred coil regions. If they were in the helical conformation, then they preferred to be within N-terminal segments. Proteins 1999;37:30-43.

Amino Acids↗
PubMed1999

Strain in protein structures as viewed through nonrotameric side chains: II. effects upon ligand binding.

The relation between the spatial positioning of nonrotameric residues and ligands was studied in 112 tertiary structures of protein-ligand complexes with a crystallographic resolution of </= 1. 8 A. Nonrotameric side chains and especially clusters of interacting nonrotameric residues were found to be associated preferentially with ligand- and substrate-binding sites. Asp, Glu, His, Met, and Asn are favored nonrotameric residue types positioned in the first 9-A shell around ligands. Comparison of 20 complexes with associated apo structures suggests that ligand binding induces nonrotamericity and, hence, strain within protein-ligand complexes. The internal energy gain is not neutralized by increased hydrogen bonding or salt-bridge formation involving side chains that become nonrotameric in the complexed structure. It is suggested that the increased internal energy might aid in the formation and ejection of enzymatic products, thereby enhancing activity. These results could prove useful in protein engineering experiments aimed at altering enzymatic activity. Proteins 1999;37:44-55.

Amino Acids↗
PubMedDate not supplied

[Transient erythroblastopenia in children: assessment of a hospital caseload].

Transient erythroblastopenia of childhood (TEC) is an acquired, self-limiting, uncommon disease, characterized by the temporary arrest of red cell production, resulting in moderate to several anemia. We retrospectively evaluated four cases of TEC, identified during an 8-year period of time in our Department of Pediatrics, including one patient, who developed TEC during the course of Kawasaki's syndrome. Clinical and hematological presentations of patients were analyzed and the most recent data of literature were reviewed. In conclusion, we suggest that a better knowledge of this rare and unique hematologic disorder of childhood may help make a correct diagnosis, avoiding unnecessary laboratory tests (e.g. bone marrow aspirate) and inappropriate therapeutic modalities.

Child↗
PubMed1975

A comparison of the heme binding pocket in globins and cytochrome b5.

Of the 85 three-dimensionally characterized residues of cytochrome b5, 51 are found to be structurally and topologically equivalent to the globin fold. When these proteins have been superimposed, the heme irons are found to be less than 1.4 A separated and the heme normals are inclined by less than 9.5 degrees. The proximal histidine of the globins and two adjacent helices are equivalent to the sixth iron ligand and adjacent helices of cytochrome b5. Larger differences in structure are observed on the distal side of the heme, coincident with the most changeable part of the globin structures. The heme itself is rotated by 53 degrees about its normal but such a change is energetically minimal and conservative as the heme side groups are not directly involved in the function of the molecules. The beta-sheet of cytochrome b5 is inserted into a corresponding cavity of the globins forming an additional lining to the heme pocket. The roughly 50 residues missing at the carboxy end of the known cytochrome b5 fragment could correspond in part to the H helix in the globins. While it would seem probable that these similarities represent divergent evolution from a primordial heme-binding protein, the possibility of structural convergence to a functionally satisfactory protein cannot be excluded.

Amino Acid Sequence↗
PubMed1975

The structure of ferrocytochrome b5 at 2.8 A resolution.

Crystals of cytochrome b5 reduced by sodium dithionite are isomorphous with the oxidized form. An electron density difference map between the two forms was calculated at 2.8 A resolution. There are no changes in main chain conformation or internal side chain orientation upon reduction. However, an ion becomes attached at the entrance of the heme crevice causing displacement of a surface lysine side chain on an adjacent molecule. The ion, identified as a cation by the nature of its coordinating ligands, appears to neutralize one of the heme propionate groups which is partially buried. It is proposed that the negatively charged propionate serves to neutralize the net formal positive charge on the heme iron in the oxidized cytochrome and that the neutralization of the heme iron upon reduction then leads to binding of a cation to the propionate.

Animals↗
PubMed2004

[Rectosigmoidectomy and end to end coloanal anastomosis with mechanical stapler for treatement of Hirschsprung disease].

UNLABELLED: The experience of the Pediatric Surgical Service of the Materno Infantil University Hospital from Málaga on surgical treatment of the Hirschsprung disease by means of a modified technique of Swenson and Rehbein operations is presented. MATERIAL AND METHODS: Between 1992 and 2001 25 patients were operated of a rectosigmoidectomy. Of them, 23 were diagnosed of Hirschsprung's disease, one suffered a rectal angiodisplasia and the other one presented with a rectal stenosis secondary to a previous rectosigmoidectomy. In all of them a transabdominal rectosigmoidectomy with coloanal end to end anastomosis by means of a circular intraluminal stapler was performed. In 10 of them (group A), a modified Rehbein operation with intraabdominal anastomosis was performed. In the remaining 15 patients (group B), a modified Swenson operation with exteriorization of the aganglionic colon through the anus and extrabdominal anastomosis was performed. RESULTS: The postoperative course was evaluated by measuring the postoperative fasting time and the first spontaneous deposition. The medium hospital stay was of 9 days, nevertheless in 16 patients (64%) was lower than 7 days. The postoperative complications are presented. It consists in 1 anastomotic leakage (4%), postoperative enterocolitis 1 case (4%) and transient anastomotic stenosis in 4 patients (16%). All of them were treated with conservative treatment except one case of stenosis which needed a sphincterotomy. CONCLUSIONS: The rectosigmoidectomy and coloanal end to end anastomosis with endoluminal stapler is a safe and easy to do technique to treat the Hirschsprung's disease allowing a deep rectal resection which is very difficult to achieve by manual suture. The anastomosis is located in and extraperitoneal position, with a minimum risk of peritoneal involvement in case of anastomotic leakage. The patients presented a fast recovery, a minimum of complications and good functional result.

Anastomosis, Surgical↗
PubMed1998

Association between insulin dependent diabetes mellitus and coeliac disease. A study on 175 diabetes patients.

BACKGROUND: The association between diabetes mellitus and coeliac disease has been known for many years. In a random group of 175 insulin dependent diabetes mellitus patients of varying ages the following tests have been carried out: serum antigliadin antibodies (AGA) of IgA and IgG class, antireticulin antibodies (ARA) and antiendomisyum antibodies (AEA), both of IgA class. MATERIALS AND METHODS: The patients, 85 males and 90 females, had ages ranging from 1 yr to 30 yrs (102 in paediatric age--mainly between 6 and 14 years--and 73 adults). Patients with pathological values for AEA and/or ARA underwent an intestinal biopsy. RESULTS: Out of 175 patients studied, 21 had pathological values for AEA with or without pathological values for ARA and AGA, and 2 patients had only pathological values for ARA. 23 patients (21 with pathological values for AEA with or without ARA and AGA, 2 only for ARA ) underwent intestinal biopsy, all patients with pathological values for AEA had villous atrophy. The prevalence of coeliac disease among IDDM patients was 8.8% (95% CI 3.3 to 14.3) for the children and 16.4% (95% CI 7.9 to 24.9) for the adults. In patients with mucous atrophy, ARA, AGA IgA and IgG were pathological in 85%, 71% and 61% respectively. Symptoms and insulin requirements in all patients affected by coeliac disease before and after one year on a gluten free diet were also evaluated. The patients had clinical features with prevalently one or only few atypical symptoms which disappeared on a gluten free diet. Insulin requirements after one year on a gluten free diet appeared unchanged in coeliac patients. CONCLUSIONS: The need to screen all diabetic patients for coeliac disease is underlined.

Journal Article↗
PubMed1991

Effect of oral melatonin treatment on the seasonal physiology of pony stallions.

This study tested the role of melatonin in the regulation of seasonal physiological change in the pony stallion. Four 3-year-old, Welsh Mountain pony stallions were housed initially under the prevailing short-day photoperiod in December (8 of light [L]:16 h of darkness [D]) before being transferred to long days (16L:8D) on 13 January for the remaining 22 weeks of the study. On Day 76 (11 weeks later) the stallions began an 11-week period of daily melatonin treatment (20 mg orally, 8 h after lights on). Marked changes in mean plasma testosterone, beta-endorphin and cortisol concentrations occurred in response to long days and to subsequent melatonin treatment. Photostimulation produced a sharp rise in overall mean daily testosterone to a peak of 6.74 nmol/litre by Day 30. Values then fell to a nadir (3.17 nmol/litre) by Day 85, suggesting a role for melatonin in the termination of breeding activity in the horse. Cortisol and beta-endorphin values remained low throughout the first 11 weeks, but by Day 105 (Day 30 of melatonin treatment) concentrations had risen sharply, attaining a peak on Day 125 (510 pg beta-endorphin/ml, 50 ng cortisol/ml). Concentrations of both hormones had fallen by Day 77 of melatonin treatment (Day 152), perhaps as a result of refractoriness. Parallelism between beta-endorphin and cortisol suggests a pituitary origin for peripheral beta-endorphin. Diurnal variation in cortisol was observed under long days but no change in beta-endorphin was detected. Long days and melatonin treatment stimulated shedding of the winter and summer coats respectively, whereas growth rate was increased (2.03 kg/week) during the period of melatonin treatment relative to that of long days only (0.37 kg/week). The study provides evidence that the diurnal pattern of melatonin secretion mediates the reproductive and non-sexual responses to photoperiodic change in pony stallions.

Administration, Oral↗
PubMed1989

The primary structure of human secretogranin II, a widespread tyrosine-sulfated secretory granule protein that exhibits low pH- and calcium-induced aggregation.

Secretogranin II (previously also called chromogranin C) is a tyrosine-sulfated secretory protein found in secretory granules in a wide variety of endocrine cells and neurons. Here, we have determined the primary structure of human secretogranin II from a full length cDNA clone and have investigated its properties, predicted from the sequence, by studying the behavior of purified secretogranin II under conditions characteristic of the milieu of secretory granules. Analysis of a 2.35-kilobase cDNA clone isolated from a human pituitary library and identified as secretogranin II by various criteria showed that human presecretogranin II is a 617-residue polypeptide containing an NH2-terminal located signal peptide. Secretogranin II lacks the disulfide-bonded loop structure near the NH2 terminus which is conserved in chromogranin A and chromogranin B (secretogranin I), two other widespread constituents of neuroendocrine secretory granules, but like the latter two proteins contains (i) an -E-N/S-L-X-A/D-X-D/E-X-E-L- motif and (ii) multiple potential dibasic cleavage sites for the generation of smaller, perhaps biologically active peptides. Another structural feature that secretogranin II shares with chromogranin A and chromogranin B (secretogranin I) is the abundance of acidic residues all along the polypeptide chain whose negative charge must somehow be neutralized to allow condensation and packaging of the protein into secretory granules. Experiments with purified secretogranin II showed that in the presence of 10 mM calcium at pH 5.2, conditions characteristic of the milieu of neuroendocrine secretory granules, this protein formed aggregates. Immunoglobulin G, a secretory protein that in vivo is not packaged into secretory granules, did not form aggregates under these in vitro conditions and was excluded from the secretogranin II aggregates. Very little aggregation of secretogranin II was observed in the absence of calcium at pH 5.2 or in the presence of calcium at neutral pH. In vivo, ammonium chloride, which is known to neutralize the pH of acidic intracellular compartments, inhibited the packaging of newly synthesized secretogranin II into secretory granules. Our results suggest that the low pH- and calcium-induced aggregation of secretogranin II may be important for the organization of the secretory granule matrix and raise the possibility that aggregation of secretogranin II may be involved in its sorting to secretory granules.

Amino Acid Sequence↗
PubMed1985

Identification of a trpG-related glutamine amide transfer domain in Escherichia coli GMP synthetase.

An improved method was developed to align related protein sequences and search for homology. A glutamine amide transfer domain was identified in an NH2-terminal segment of GMP synthetase from Escherichia coli. Amino acid residues 1-198 in GMP synthetase are homologous with the glutamine amide transfer domain in trpG X D-encoded anthranilate synthase component II-anthranilate phosphoribosyltransferase and the related pabA-encoded p-aminobenzoate synthase component II. This result supports a model for gene fusion in which a trpG-related glutamine amide transfer domain was recruited to augment the function of a primitive NH3-dependent GMP synthetase. Sequence analyses emphasize that glutamine amide transfer domains are thus far found only at the NH2 terminus of fused proteins. Two rules are formulated to explain trpG and trpG-related fusions. (i) trpG and trpG-related genes must have translocated immediately up-stream of genes destined for fusion in order to position a glutamine amide transfer domain at the NH2 terminus after fusion. (ii) trpG and trpG-related genes could not translocate adjacent to a regulatory region at the 5' end of an operon. These rules explain known trpG-like fusions and explain why trpG and pabA are not fused to trpE and pabB, respectively. Alignment searches of GMP synthetase with two other enzymes that bind GMP, E. coli amidophosphoribosyltransferase and human hypoxanthine-guanine phosphoribosyltransferase, suggest a structurally homologous segment which may constitute a GMP binding site.

Amidophosphoribosyltransferase↗
PubMed1986

Sequence analysis and characterization of a maize gene encoding a high-sulfur zein protein of Mr 15,000.

We have isolated a gene coding for a sulfur-rich zein protein from a maize genomic library. The nucleotide sequence of this gene predicts a protein composed of 180 amino acids, including a 20-amino acid signal peptide. As is true of other zeins, there are no intervening sequences in the gene. Comparison of the nucleotide sequence of this gene with that of a homologous cDNA clone revealed only a single difference resulting in a valine/alanine substitution. The Mr 15,000 zein contains no repetitive nucleotide sequences and shows no homology with genes encoding the Mr 22,000 and 19,000 zeins. Circular dichroism analysis of the Mr 15,000 zein protein revealed that it is composed primarily of beta and turn structures. This gene has a short region of nucleotide sequence homology to the cysteine-rich domain of the Mr 27,000 zein, as well as the cysteine-containing barley B-hordein.

Amino Acid Sequence↗