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Biomedical subjects

M Paoli

Publications and source records attributed to M Paoli.

At least 19 recordsLinked to original sources
PubMed2001

Protein folds propelled by diversity.

Many proteins involved in key biological processes are modular in nature. A group of these, the beta-propeller proteins, fold by packing 4-stranded beta-sheets in a circular array. The members of this group are increasingly numerous and, although their modular building blocks all preserve the same basic conformation, they do not have similar sequences. These proteins have extreme functional and phylogenetic diversity. Here, features of the beta-propeller fold are reviewed through comparisons of available structural coordinates. Structure-based sequence alignments combined with analyses of superpositions of individual modular units reveal conserved general features such as hydrogen bonds, beta-turns and positions of hydrophobic contacts. The lack of significant sequence identity is compensated by sets of interactions which stabilise the fold differently in distinct structures. Re-occurring aspartates make contacts to exposed backbone amides in turns or peptide connections within the same sheet. The sole factor responsible for the number of sheets that assemble in the array is the size of the hydrophobic residues that pack into the cores between the sheets. Whilst there is no overall sequence conservation, it may be possible to detect new members of this fold through sequence searches that take into account the repeated nature of the modular assembly as well as the positions of hydrophobic residues and H-bonding side chains.

Amino Acid Sequence↗
PubMed2001

Decreased bone mineral density and bone formation markers shortly after diagnosis of clinical type 1 diabetes mellitus.

We recently demonstrated that children with type 1 diabetes mellitus (DM) have decreased lumbar spine bone mineral density (BMD) as early as four years after clinical diagnosis of the disease. In order to determine whether osteopenia is already present in patients very early on after diagnosis of clinical DM, we evaluated the bone mineral status of a group of newly diagnosed children (5.8 +/- 1.5 mo after diagnosis). We studied 23 prepubertal children (7 M, 16 F) with a mean chronological age of 9.5 +/- 2.2 yr and a mean glycosylated hemoglobin of 8.9 +/- 2.4%. Lumbar spine and femoral neck BMD were measured by dual X-ray absorptiometry, while bone turnover was assessed by the determination of the serum concentration of the carboxy-terminal propeptide of type I collagen (PICP) and the carboxy-terminal cross-linked telopeptide of type I collagen (N-telopeptide). Results were compared to those of age, height, and pubertal status matched controls. Lumbar spine BMD Z-scores were decreased in patients compared to controls (Z-scores of -0.89 +/- 1.2, with 10 of 22 patients showing values >1 SD below the mean). When lumbar spine Z-scores were analyzed in those patients with <3 months or > or =3 months since diagnosis of DM a significant difference was noticed between groups (-0.648 +/- 1.12 vs -1.267 +/- 1.17; p <0.02). No significant differences were noted in femoral neck BMD and total BMD between groups. Serum PICP levels were decreased when compared to controls (233.6 +/- 39.3 vs 375.9 +/- 50.7 microg/l; p <0.002), while serum N-telopeptide concentrations, although increased, were not significantly different (9.3 +/- 1.3 vs 5.7 +/- 1.5 microg/l). In summary, early on after the diagnosis of type 1 DM, children present with decreased lumbar spine BMD and decreased bone formation markers.

Biomarkers↗
PubMed2001

[Concentration of thyrotropic hormone and free thyroxin in children with Down's syndrome].

The incidence of hypothyroidism is higher among children with Down syndrome than among children in the general population. The frequency of hypothyroidism is higher in the areas of endemic goiter than in other areas. The aim of this paper was to study the concentrations of TSH and FT4 in children with Down syndrome residents of Mérida, a region of Venezuelan Andes. At the Centro de Estudio y Prevención del Retardo Mental y Alteraciones en el Desarrollo (CEPREMAD), the thyroid function was studied in 48 children (1 month to 6 years old), who had Down syndrome, and in 123 healthy children of similar ages. All the children were referred to the Center for thyroid function evaluation. Two (4.2%) of the 48 children with Down syndrome had congenital hypothyroidism and 22 (45.8%) had subclinical hypothyroidism (high concentration of thyrotropin-TSH). Among the control children, only 14% had elevated levels of TSH. There were no differences in relation to the gender. In conclusion in children with Down syndrome, the frequency of high concentrations of TSH was three times higher than the frequency among the healthy children. The frequency of hypothyroidism was similar to that found in areas without endemic goiter.

Biomarkers↗
PubMed1999

Allele typing of short tandem repeats by capillary electrophoresis.

Capillary electrophoresis with laser-induced fluorescence was applied to the analysis of six STRs and the amelogenin sex test with the purpose of verifying accuracy and precision of the sizing method with the GS500 internal standard. Sequenced dye-labeled, PCR-amplified alleles from amelogenin, HumVWA31, HumTH01, HumF13A01, HumFIBRA, D21S11 and HumCSF1PO loci were run several times on the same capillary and on multiple capillaries and the offset of computer-measured fragment sizes from the expected molecular weights was calculated and analysed. All loci except D21S11 showed a poor degree of accuracy. Precision results from run-to-run and day-to-day injections displayed a maximum standard deviation (SD) > 0.15 nt for HumVWA31, HumF13A01, D21S11 and HumFIBRA, although the maximum range of calculated sizes in multiple runs was lower than 1 basepair. No variation in precision was observed according to the quality of the DNA template. Allele typing by comparison with allelic ladders for each locus is recommended.

Alleles↗
PubMed1999

Fix L, a haemoglobin that acts as an oxygen sensor: signalling mechanism and structural basis of its homology with PAS domains.

Fix L, which contains a haemoglobin domain homologous to the PAS family and a histidine kinase domain, forms, with Fix J, a two-component signalling complex that regulates expression of nitrogenase genes in Rhizobium. Spin transitions of its haem iron trigger stereochemical changes in and around the haem that, together with steric effects, control the activity of the kinase. Homology with the PAS family is based on a common core of about 20 structurally equivalent sites from which polar residues are excluded.

Animals↗
PubMed1999

Crystal structure of hemopexin reveals a novel high-affinity heme site formed between two beta-propeller domains.

The ubiquitous use of heme in animals poses severe biological and chemical challenges. Free heme is toxic to cells and is a potential source of iron for pathogens. For protection, especially in conditions of trauma, inflammation and hemolysis, and to maintain iron homeostasis, a high-affinity binding protein, hemopexin, is required. Hemopexin binds heme with the highest affinity of any known protein, but releases it into cells via specific receptors. The crystal structure of the heme-hemopexin complex reveals a novel heme binding site, formed between two similar four-bladed beta-propeller domains and bounded by the interdomain linker. The ligand is bound to two histidine residues in a pocket dominated by aromatic and basic groups. Further stabilization is achieved by the association of the two beta-propeller domains, which form an extensive polar interface that includes a cushion of ordered water molecules. We propose mechanisms by which these structural features provide the dual function of heme binding and release.

Animals↗
PubMed1999

[Multinucleate cell angiohistiocytoma].

INTRODUCTION: Multinucleate cell angiohistiocytoma is a rare benign vascular proliferation. We report a case. CASE REPORT: A 75-year-old woman presented violaceous papules on the right thigh. Histological examination showed a proliferation of small blood vessels with multinucleated cells in the dermis and confirmed the diagnosis of multinucleate cell angiohistiocytoma. DISCUSSION: Multinucleate cell angiohistiocytoma is a rare benign vascular tumor first described in 1985 often confused with Kaposi's sarcoma. Clinically it is characterized by violaceous papules on acral sites and face in elderly women. Histological examination shows an increased number of blood vessels together with mononucleated and multinucleated histiocyte-like cells in the dermis. Reviewing the literature we describe the main clinical and histopathologic features of this disorder.

Aged↗
PubMed1998

A comparison between horizontal splint and repositioning splint in the treatment of 'disc dislocation with reduction'. Literature meta-analysis.

We reviewed the literature from 1985 to 1996 concerning the preliminary treatment of disc dislocation with reduction (DDWR) by means of occlusal splints, pinpointing two main methods. The conflicting results of many papers induced us to make a literature meta-analysis of those articles with the necessary requirements in order to verify the effectiveness of the two therapeutic means more frequently used in DDWR; the repositioning splint and the bite plane. A statistical comparison between the two kinds of treatment has demonstrated that the repositioning splint is more effective both in the resolution of the articular click and of the pain at a level of P < or = 0.00001, which is noteworthy and highly significant.

Confidence Intervals↗
PubMed1998

The stereochemical mechanism of the cooperative effects in hemoglobin revisited.

In 1970, Perutz tried to put the allosteric mechanism of hemoglobin, proposed by Monod, Wyman and Changeux in 1965, on a stereochemical basis. He interpreted their two-state model in terms of an equilibrium between two alternative structures, a tense one (T) with low oxygen affinity, constrained by salt-bridges between the C-termini of the four subunits, and a relaxed one (R) lacking these bridges. The equilibrium was thought to be governed primarily by the positions of the iron atoms relative to the porphyrin: out-of-plane in five-coordinated, high-spin deoxyhemoglobin, and in-plane in six-coordinated, low-spin oxyhemoglobin. The tension exercised by the salt-bridges in the T-structure was to be transmitted to the heme-linked histidines and to restrain the movement of the iron atoms into the porphyrin plane that is necessary for oxygen binding. At the beta-hemes, the distal valine and histidine block the oxygen-combining site in the T-structure; its tension was thought to strengthen that blockage. Finally, Perutz attributed the linearity of proton release with early oxygen uptake to the sequential rupture of salt-bridges in the T-structure and to the accompanying drop in pKa of the weak bases that form part of them. Almost every feature of this mechanism has been disputed, but evidence that has come to light more than 25 years later now shows it to have been substantially correct. That new evidence is reviewed below.

Allosteric Regulation↗
PubMed1997

Tension in haemoglobin revealed by Fe-His(F8) bond rupture in the fully liganded T-state.

In 1972, Perutz proposed that the low affinity of T-state haemoglobin is caused by tension in the bond between the iron and the proximal histidine, restraining the Fe from moving into the porphyrin plane on binding oxygen. This proposal has often been disputed. If such tension does exist, it will be manifest in the liganded T-state. Here we describe the structure of the fully liganded T-state cyanide complex of haemoglobin, in which the Fe-proximal histidine bond in the alpha-subunits, but not in the beta-subunits, is ruptured. This rupture uncouples the structural changes at the alpha-haem from those in the globin and the beta-haem, and demonstrates unequivocally the existence of tension and its transmission through this bond.

Binding Sites↗
PubMed1997

Spectroscopic evidence for a conformational transition in horseradish peroxidase at very low pH.

Resonance Raman (RR), electronic absorption, and circular dichroism (CD) spectroscopies of the ferric, ferrous, and ferrous-CO forms of horseradish peroxidase (HRP-C) at pH 3.1 are reported. The CD spectra in the UV region show only a small decrease in the alpha-helical content upon pH lowering, whereas dramatic changes are observed in the Soret region. The final form of ferric HRP-C is 5-coordinate high-spin heme whose histidine ligand is replaced by a water ligand with a polar character. The electronic and CD spectra show the presence of an intermediate form with a 6-coordinate heme. Therefore, the cleavage of the proximal Fe-imidazole bond is preceded by the binding of a distal water molecule. For the ferrous form of HRP-C, the pH-dependence of the absorption spectra revealed only the native form in the range pH 5-7 and an unfolded form with a Soret maximum at 383 nm at pH 3.1. An intermediate state, characterized by a Soret maximum at 424 nm, was observed only in a transient way, within a few milliseconds. A metastable and a final species are observed also for the ferrous-CO complex at pH 3.1, as proved by isosbestic points in the electronic absorption spectra. The two forms show different RR nu(Fe-C) and IR nu(CO) modes. The metastable form corresponds to a heme where histidine is replaced by water. The final form is due to the displacement of the water ligand by the proximal histidine. We propose a kinetic model to account for our results at pH 3.1 for the ferric, ferrous, and ferrous-CO forms.

Circular Dichroism↗
PubMed1997

Effectiveness and limitations of the use of the gonadotropin-releasing hormone agonist leuprolide acetate in the diagnosis of delayed puberty in males.

In order to evaluate the effectiveness of the gonadotropin-releasing hormone agonist leuprolide acetate in distinguishing gonadotropin deficiency from delayed puberty, a single subcutaneous dose of 20 micrograms/kg of leuprolide acetate was administered at 07.00 h to 14 patients with constitutionally delayed puberty and to 8 gonadotropin-deficient subjects, and serum gonadotropin and testosterone levels were determined at baseline and 1,2,3,6,12, and 24 h thereafter. The increase in gonadotropin and testosterone levels was significant in patients with delayed puberty, so that the mean peak luteinizing hormone and to a lesser degree the mean peak testosterone levels clearly differentiated normally delayed from gonadotropin-deficient puberty. However, when the peak gonadotropin and testosterone concentrations were analyzed individually, there was a considerable overlap between the two groups of males, limiting the usefulness of this test.

Adolescent↗
PubMed1997

Mutagenicity and chemical analysis of airborne particulate matter collected in Pisa.

The genotoxic effects of airborne particulate samples collected from two urban areas during various traffic intensity levels were evaluated using the yeast Saccharomyces cerevisiae (D7 strain) and Salmonella typhimurium (TA98 and TA100 strains). Standard protocols were used, in compliance with recent legislation. Airborne particulate data reveal that genotoxic effects were more evident in the samples collected in the area with intense moving traffic than in the area with limited traffic. Particulate, benzene, toluene, NO2, CO, and heavy metal determinations in these two areas show that their concentrations are related to the intensity of traffic.

Air Pollutants↗
PubMed1996

Crystal structure of T state haemoglobin with oxygen bound at all four haems.

The cooperative binding of oxygen by haemoglobin results from restraints on ligand binding in the T state. The unfavourable interactions made by the ligands at the haems destabilise the T state and favour the high affinity R state. The T <==> R equilibrium leads, in the presence of a ligand, to a rapid increase in the R state population and therefore generates cooperative binding. There is now considerable understanding of this phenomenon, but the interactions that reduce ligand affinity in the T state have not yet been fully explored, owing to the difficulties in preparing T state haemoglobin crystals in which all the subunits are oxygenated. A protocol has been developed to oxygenate deoxy T state adult human haemoglobin (HbA) crystals in air at 4 C at all four haems without significant loss of crystalline order. The X-ray crystal structure, determined to 2.1 A spacing, shows significant changes in the alpha and beta haem pockets as well as changes at the alpha(1)beta(2) interface in the direction of the R quaternary structure. Most of the shifts and deviations from deoxy T state HbA are similar to, but larger than, those previously observed in the T state met and other partially liganded T state forms. They provide clear evidence of haem-haem interaction in the T state.

Adult↗
PubMed1995

Resonance Raman studies of the heme active site of the homodimeric myoglobin from Nassa mutabilis: a peculiar case.

A spectroscopic investigation by resonance Raman has been carried out at pH 7.0 in 0.1 M phosphate buffer on the cooperative homodimeric myoglobin from Nassa mutabilis. The study has been performed on the unligated ferrous form, as well as on the ligated species MbO2 and MbC, and on the ferric form met-Mb. Two v(C = C) vinyl stretching modes have been observed in all the investigated forms, reflecting different degrees of vinyl conjugation with the porphyrin ring, as a consequence of a strongly asymmetric environment for the two side groups of the heme. Furthermore, the ferric form displays a hexacoordinate low-spin heme, which suggests the presence of an endogenous ligand bound to the Fe atom. The frequency of the v(Fe-Im) stretching mode of Mb from Nassa mutabilis shifts down by 4 cm-1 as compared with that of horse heart myoglobin, reflecting a protein-induced proximal strain as a result of heme-heme interaction due to the close proximity of the two hemes in the dimer. The lower frequency of the v(Fe-Im) stretching mode agrees well with the lower affinity for oxygen binding found for Nassa mutabilis Mb and with the slight heme core expansion with respect to horse heart Mb, suggesting a critical role for the Fe-His bond on the heme's function and structure.

Animals↗
PubMed1995

Bone mineral density of prepubertal age girls with Turner's syndrome while on growth hormone therapy.

Bone mineral densities and growth velocities of young girls with Turner's syndrome treated with recombinant human growth hormone at an age before the decreased levels of estrogens secondary to their ovarian failure could contribute to osteopenia were studied. Twelve patients with a mean chronological age of 8.9 +/- 0.9 years and a mean bone age of 6.9 +/- 0.8 years received growth hormone therapy for over 2 years (0.5 IU/kg/week s.c.) Mean growth velocities increased significantly from a baseline level of 3.5 +/- 0.4 cm/year to 6.4 +/- 0.3 and 5.7 +/- 0.4 cm/year at 12 and 24 months of therapy, while height SDS improved from -3.1 +/- 0.4 at baseline to -2.7 +/- 0.3 and -2.4 +/- 0.3 at 12 and 24 months, respectively. Total bone calcium as well as cortical bone mineral density of our density of our patients while on recombinant human growth hormone were similar to that of a control group of prepubertal healthy growth children paired for bone age and height; bone density of trabecular bone was however increased in our patients when compared to healthy controls (0.791 +/- 0.04 vs. 0.669 +/- 0.02 g/cm2; p < 0.025). We conclude from our study that the bone mineral status of young girls with Turner's syndrome on growth hormone therapy seems to be normal.

Age Determination by Skeleton↗