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Biomedical subjects

L Chiche

Publications and source records attributed to L Chiche.

At least 19 recordsLinked to original sources
PubMed1998

Formation of native disulfide bonds in endothelin-1. Structural evidence for the involvement of a highly specific salt bridge between the prosequence and the endothelin-1 sequence.

The [Lys-Arg]-endothelin-1 analogue (KR-ET-1) yields almost selectively the native disulfide pattern (96%), in contrast to endothelin-1 (ET-1) that gives at least 25% of the non-native disulfide pattern. We have previously shown that the carboxylate-state structure of KR-ET-1 is more constrained and stabilized by a salt bridge between Arg(-1) and the Asp8 or Glu10 side chain [Aumelas et al. (1995) Biochemistry 34, 4546-4561]. To identify this salt bridge and its potential involvement in the disulfide bond formation, [E10Q], [D18N], and [D8N] carboxamide analogues were studied, which led to the unambiguous identification of the Arg(-1)-Asp8 salt bridge. Furthermore, while [E10Q] and [D18N] analogues gave a high yield of the native isomer (>/=90%), the [D8N] analogue afforded a ratio of the two isomers close to that observed for ET-1 (68%) [Kubo et al. (1997) Lett. Pept. Sci. 4, 185-192]. Assuming that the formation of disulfide bonds occurs in a thermodynamically controlled step, we have hypothesized that the Arg(-1)-Asp8 salt bridge and concomitant interactions could be responsible for the increase in yield of the native isomer of KR-ET-1. In the present work, we describe the structural studies of the carboxamide analogues and of the minor non-native KR-ET-1 isomer. On the basis of 1H NMR and CD spectra as a function of pH, [E10Q] and [D18N] analogues display a conformational change similar to that of the parent peptide, whereas the structure of the [D8N] analogue is unchanged. For the non-native isomer, we measured a lower helical content than for the native isomer and observed a marked difference in the orientation of the KRCSC backbone. In addition, no salt bridge was experimentally observed. Altogether, these results allow us to hypothesize that the salt bridge between two highly conserved residues, one belonging to the prosequence [Arg(-1)] and the other to the mature sequence [Asp8], is involved in the formation of the native disulfide isomer of ET-1. The involvement of the prosequence in the formation of the native disulfide isomer strongly suggests that, in the maturation pathway of ET-1, cleavage of the Arg52-Cys53 amide bond occurs after native disulfide bond formation.

Amino Acid Sequence↗
PubMed1998

Solution structure of the antimicrobial peptide ranalexin and a study of its interaction with perdeuterated dodecylphosphocholine micelles.

Ranalexin, a 20-residue peptide isolated from the skin of the bullfrog Rana catesbeiana displays antimicrobial activity. This peptide contains two cysteine residues in positions 14 and 20 linked by a disulphide bridge. Ranalexin was chemically synthesised and close antimicrobial activities were measured for the reduced and oxidised forms. The solution structure of ranalexin was determined by using circular dichroism, proton NMR spectroscopy and molecular modelling techniques. The reduced and oxidised forms of ranalexin are mainly unstructured in water but display an alpha-helical structure spanning residues 8-15 and 8-17, respectively, in a trifluoroethanol/water mixture (3:7, by vol.). Ranalexin was found to interact with micelles of dodecylphosphocholine and to adopt a similar helical structure. Moreover, slow-exchanging amide protons located on the same side of the helix suggest that the hydrophobic face of the helix lies on the micelle surface. Hydrophobic residues of the poorly structured N-terminal part which are important for the biological activity are also involved in the interaction with micelles. Taken together, the results suggest that the disulphide bond does not strongly affect either the conformation or the antimicrobial activity of ranalexin.

Amino Acid Sequence↗
PubMed1998

Laparoscopic anatomical hepatic resection. Report of four left lobectomies for solid tumors.

Four patients underwent a laparoscopic left hepatic resection for solid tumor, two for metastasis from colonic cancer, and two for focal nodular hyperplasia (final diagnosis). The procedure was performed according to the rules of conventional hepatic surgery and cancer surgery. No blood transfusion was necessary. No surgical complication occurred. In malignant disease, laparoscopy allows a good staging and the performance of a real no-touch technique; the specimen is removed in a plastic bag without contact to the abdominal wall. In symptomatic benign disease the esthetic benefit of the laparoscopic approach is real. In asymptomatic benign disease, laparoscopy could allow large biopsies in the case of uncertain diagnosis or dangerous resection. It allows safe resections in the case of small, well-located tumors. This approach requires sophisticated material and extensive experience in both laparoscopy and hepatobiliary surgery.

Adult↗
PubMed1998

Hinge-bending motions in annexins: molecular dynamics and essential dynamics of apo-annexin V and of calcium bound annexin V and I.

Annexins are homologous proteins that bind to membranes in a calcium dependent manner, but for which precise physiological roles have yet to be defined. Most annexins are composed of a planar array of four homologous repeats, each containing five alpha-helices and associated into two modules. Annexin V forms a voltage-gated calcium channel in phospholipid bilayers. It has been proposed that the hydrophilic pore in the centre of the molecule may represent the ion conduction pathway and that a hinge movement in annexin V causes a variation of the inter-module angle and opens the calcium ion path. Here we present the results of molecular dynamics simulations of apo-annexin V and of calcium-bound annexin V and annexin I. The three simulations show significant differences in conformation and dynamics. The essential dynamics method was used to study the essential subspace of annexin V and showed that one of the essential motions corresponds to the postulated hinge motion. The hinge residues were located between repeats but belong to helices rather than to the links between helices. Calcium binding to annexin V led to a limitation of this hinge motion with more open conformations being favoured.

Amino Acids↗
PubMed1998

Substitution of Ala564 in the first zinc cluster of the deoxyribonucleic acid (DNA)-binding domain of the androgen receptor by Asp, Asn, or Leu exerts differential effects on DNA binding.

In the androgen receptor of a patient with androgen insensitivity, the alanine residue at position 564 in the first zinc cluster of the DNA-binding domain was substituted by aspartic acid. In other members of the steroid receptor family, either valine or alanine is present at the corresponding position, suggesting the importance of a neutral amino acid residue at this site. The mutant receptor was transcriptionally inactive, which corresponded to the absence of specific DNA binding in gel retardation assays, and its inactivity in a promoter interference assay. Two other receptor mutants with a mutation at this same position were created to study the role of position 564 in the human androgen receptor on DNA binding in more detail. Introduction of asparagine at position 564 resulted in transcription activation of a mouse mammary tumor virus promoter, although at a lower level compared with the wild-type receptor. Transcription activation of an (ARE)2-TATA promoter was low, and binding to different hormone response elements could not be visualized. The receptor with a leucine residue at position 564 was as active as the wild-type receptor on a mouse mammary tumor virus promoter and an (ARE)2-TATA promoter, but interacted differentially with several hormone response elements in a gel retardation assay. The results of the transcription activation and DNA binding studies could partially be predicted from three-dimensional modeling data. The phenotype of the patient was explained by the negative charge, introduced at position 564.

Amino Acid Sequence↗
PubMed1997

Solution structure of human p8MTCP1, a cysteine-rich protein encoded by the MTCP1 oncogene, reveals a new alpha-helical assembly motif.

MTCP1 (for Mature-T-Cell Proliferation) is the first gene unequivocally identified in the group of uncommon leukemias with a mature phenotype. The three-dimensional solution structure of the human p8(MTCP1) protein encoded by the MTCP1 oncogene was determined by homonuclear proton two-dimensional NMR methods at 600 MHz. After sequence specific assignments, a total of 931 distance restraints and 57 dihedral restraints were collected. The location of the three previously unassigned disulfide bridges was determined from preliminary DIANA structures, using a statistical analysis of intercystinyl distances. The solution structure of p8(MTCP1) is presented as a set of 30 DIANA structures, further refined by restrained molecular dynamics using a simulated annealing protocol with the AMBER force field. The r.m.s.d. values with respect to the mean structure for the backbone and all heavy atoms for a family of 30 structures are 0.73(+/-0.28) and 1.17(+/-0.23) A, when the structured core of the protein (residues 5 to 63) is considered. The solution structure of p8(MTCP1) reveals an original scaffold consisting of three alpha helices, associated with a new cysteine motif. Two of the helices are covalently paired by two disulfide bridges, forming an alpha-hairpin which resembles an antiparallel coiled-coil. The third helix is oriented roughly parallel to the plane defined by the alpha-antiparallel motif and its axis forms an angle of approximately 60 degrees with respect to the main axis of this motif.

Computer Simulation↗
PubMed1997

Functional and structural analysis of R607Q and R608K androgen receptor substitutions associated with male breast cancer.

We previously described an androgen receptor (AR) point mutation located in the DNA-binding domain (DBD), adjacent to another AR substitution. Both were observed in two unrelated families with male breast cancer (MBC) and partial androgen insensitivity syndrome. This work was designed to determine the potential role of these two residues by in vitro study of the consequences of these two substitutions on biological functions and their structural impact at the atomic level. Mutant ARs revealed normal androgen-binding affinities and weaker DNA binding to an isolated androgen-responsive element. In cotransfection assays the mutant ARs displayed a reduced transactivation efficiency at 0.3 x 10(-10) M. Neither binding to an estrogen-responsive element nor transactivation efficiency of an ERE reporter gene was observed. Molecular modeling revealed that Arg607 and Arg608 were partially surface-exposed and located in adjacent areas in the AR-DBD complex with DNA. This is in favor of a protein-protein interaction. It is conceivable that such an interaction could be affected by mutation of one of these two arginines.

Androgens↗
PubMed1997

Small bowel obstruction: role and contribution of sonography.

The purpose of this study was to determine whether sonography provides additional clinical information in patients suspected of small bowel (SB) obstruction. During a period of 30 months, in a prospective setting, we evaluated with sonography 123 patients suspected of SB obstruction. Sonographic examinations of the entire abdomen were performed with state-of-the-art, real-time, grey-scale equipment. Fourteen patients were labelled 'gassy' and no added information was provided following abdominal ultrasound. Sonography confirmed the SB obstruction in 82 cases with 5 false positives, resulting in a specificity of 82.1 %. Sonographic examinations were negative in 27 cases with 4 false negatives and a sensitivity of 95 %. The accuracy was 91.7 % when the 'gassy' patients were excluded and 81.3 % overall. The aetiology of the ileus was detected by sonography in 13 cases of paralytic ileus (54.1 %) and in 57 cases of mechanical ileus (71.4 %). It is concluded that ultrasound, which is a non-invasive, portable and even bedside imaging procedure, appears accurate in confirming a SB obstruction and in determining the aetiology of SB obstruction.

Adolescent↗
PubMed1997

Occlusive fibromuscular disease of arteries supplying the brain: results of surgical treatment.

Occlusive fibromuscular disease (FMD) of arteries supplying the brain is a documented cause of neurologic complications. From September 1976 to December 1994, 70 patients underwent surgery for occlusive FMD involving arteries supplying the brain. Isolated dysplastic aneurysms and coilings or kinkings were not included in this series. Twenty-two patients had experienced previous nonlethal ischemic stroke, 25 patients had experienced transient ischemic attacks, and 32 patients had vertebrobasilar insufficiency with or without associated carotid symptoms. Lesions involved one (n = 36) or two (n = 29) internal carotid arteries, and one (n = 18) or two (n = 14) vertebral arteries. Twenty-seven patients had simultaneous involvement of both carotid and vertebral arteries. Ten patients had FMD at another site, four had intracranial aneurysm, and four had an aberrant right subclavian artery. Seventy-seven carotid procedures including 67 graduated intraluminal dilatations were performed and 18 vertebral arteries were revascularized. One patient (1.4%) died postoperatively from hemorrhagic stroke and two patients (2.8%) presented nonlethal stroke. Sixty-two patients were followed postoperatively from 2 to 184 months (mean 86.2 +/- 54.4). Actuarial survival rates at 5 and 10 years were 96.4 +/- 5.0% and 82.1 +/- 14.9%, respectively. Actuarial primary patency rate at 5 and 10 years was 94.3 +/- 5.5%. Actuarial probability of stroke-free survival rates at 5 and 10 years were 94.2 +/- 5.6% and 88.6% +/- 10.3%, respectively. We conclude that improvement of symptoms, prevention of stroke, and stable long-term results justify surgical treatment in symptomatic patients with FMD of arteries supplying the brain.

Adolescent↗
PubMed1997

[Digestive hemorrhage disclosing an angiodysplasia and von Willebrand disease type 2].

The authors report a case of a 76-year-old man, with not past history of abnormal bleeding, who suffered an acute, recurrent, intestinal haemorrhage from extensive angiodysplasia of the colon. Intestinal bleeding and angiodysplasia were associated with a von Willebrand's disease. Genetic analysis showed a point mutation in arginine 611 of the mature von Willebrand's factor subunit (A1 loop) confirming a von Willebrand's disease type 2.

Aged↗
PubMed1997

[Ambulatory conservative hemodynamic correction of venous insufficiency. Technique, results].

Ambulatory conservative haemodynamic correction of venous insufficiency (CHIVA) is a surgical treatment of superficial venous insufficiency designed to correct the pathological haemodynamic effects of superficial venous insufficiency apparent on standing. Surgical treatment is based on precise preoperative anatomical and haemodynamic mapping performed by duplex ultrasound, providing preoperative ultrasound-guided marking. Surgical treatment consists of dividing the hydrostatic pressure column and disconnecting venovenous shunts by ligation-section of the superficial venous network at precise points determined by the preoperative ultrasound-guided marking. This strategy should achieve a superficial venous circuit draining perfectly into the competent deep venous network. The operation is performed under local anaesthesia as an outpatient procedure and allows immediate resumption of walking, which promotes a good result due to activation of the calf muscle pump. The results of the technique are very good provided a reliable preoperative ultrasound-guided marking and a precise surgical procedure are performed. Failures are due to poor haemodynamic assessment or inappropriate surgical procedure.

Adult↗
PubMed1997

[Inflammatory aneurysms of the thoracic aorta. Surgical aspects].

In the Western world, inflammatory aneurysms account for only 1 to 5%, of all operated thoracic aorta aneurysms. Takayasu's disease is by far the commonest cause although all forms of aortitis may result in aneurysm formation. Usually observed in young patients, these aneurysms are suitable for often major surgery with results that are globally better than in degenerative or dissecting aneurysms. However, they pose, two specific problems: the progression of the inflammatory disease which may require pre- and/or post-operative steroid therapy and that of the risk, at least in theory, of a late pseudo-aneurysm, which justifies regular long-term follow-up after surgery.

Aneurysm, False↗
PubMed1996

Synthesis and solution structure of the antimicrobial peptide protegrin-1.

Protegrins are members of a family of five Cys-rich, cationic antimicrobial peptides recently isolated from porcine cells. We have synthesised an 18-amino-acid peptide that corresponds to protegrin-1. After Cys oxidation, the peptide has bactericidal activity against gram-positive and gram-negative bacteria, similar to that described for the natural peptide. The solution structure of protegrin-1 was investigated by means of 1H-NMR spectroscopy in water and in (CD3)2SO, with distance-geometry and simulated-annealing calculations. The C6-C15 and C8-C13 disulfide pattern was determined on the basis of NMR-derived constraints. These two parallel disulfide bridges stabilised a beta-sheet structure which comprised two antiparallel strands (residues 5-9 and 12-16) linked by a distorted beta-turn (residues 9-12). The N-terminus and C-terminus were essentially disordered. The distribution of hydrophobic and hydrophilic residues at the peptide surface was found to be a structural feature shared with tachyplesin-1, a related peptide which displays cytolytic activity, and, to a lesser extent, with mammalian defensins. These findings led us to assume that the distribution pattern could be required for the cytolytic activity of these peptides.

Amino Acid Sequence↗
PubMed1996

Change in membrane permeability induced by protegrin 1: implication of disulphide bridges for pore formation.

Protegrin 1 (PG-1) is a naturally occurring cationic antimicrobial peptide that is 18 residues long, has an aminated carboxy terminus and contains two disulphide bridges. Here, we investigated the antimicrobial activity of PG-1 and three linear analogues. Then, the membrane permeabilisation induced by these peptides was studied upon Xenopus laevis oocytes by electrophysiological methods. From the results obtained, we concluded that protegrin is able to form anion channels. Moreover, it seems clear that the presence of disulphide bridges is a prerequisite for the pore formation at the membrane level and not for the antimicrobial activity.

Amino Acid Sequence↗
PubMed1996

Molecular modeling and in vitro investigations of the human androgen receptor DNA-binding domain: application for the study of two mutations.

In two families with complete androgen insensitivity, we have identified naturally occurring point mutations in the human androgen receptor gene that encode amino acid substitutions within the DNA-binding domain. The two amino acid substitutions, a valine to phenylalanine and a leucine to proline, occur at positions 581 and 616, respectively, of the androgen receptor. The mutations were recreated by site-directed mutagenesis. Expression of the mutants androgen receptors in COS 7 and CV 1 cells revealed a normal size 110-kDa receptor protein on Western blots, normal androgen binding capacities and affinities, but absence of binding to target DNA on electrophoretic mobility shift assays. In cotransfection assays, the mutant ARs failed to activate transcription of an androgen-responsive reporter gene. To study the possible structural impact of these mutations, three-dimensional models of the normal androgen receptor and of each mutant were built by homology with the glucocorticoid receptor. Analysis of the models predicts that mutation Val581Phe would affect interaction between the protein and DNA, whereas the Leu616Pro mutation would more likely be involved in destabilizing the protein structure or protein dimerization. Taken together, the experimental investigations and the molecular modeling studies of the mutant androgen receptors observed in families with complete androgen insensitivity syndrome, highlight the role of Val-581 and Leu-616 in receptor structure and function.

Base Sequence↗
PubMed1996

Pouch-related fistula following restorative proctocolectomy.

Prognostic factors and outcome of pouch-related fistula were analysed from a series of 21 patients, 20 of whom had an ileal J pouch manually anastomosed to the dentate line following mucosectomy. Fistula occurred more often after pouch formation for ulcerative colitis than for familial adenomatous polyposis. In 6 patients the fistula occurred more than 5 months after closure of the diverting loop ileostomy. The origin of the leak was the anastomosis in 14 patients, the vertical staple line in two and the end of the efferent limb in five. Nine forms of treatment were utilized and these were successful in 11 patients and unsuccessful in ten including three pouch excisions. Adverse prognostic factors were late fistula, the presence of an enterocutaneous or a pouch-vaginal fistula track, and diagnosed or suspected Crohn's disease. Resolution of the fistula followed none of six diverting loop ileostomies performed alone, three of 33 attempted drainage procedures, four of ten direct closures, and four of five repeat ileal pouch-anal anastomoses. It is concluded that an aggressive therapeutic approach using repeat ileal pouch-anal anastomosis increases the success rate.

Adenomatous Polyposis Coli↗
PubMed1996

Rational choice of molecular dynamics simulation parameters through the use of the three-dimensional autocorrelation method: application to calmodulin flexibility study.

We examined the effects of several adjustable parameters for use in molecular dynamics simulations of proteins using both standard criteria (radius of gyration, root mean square deviation from starting coordinates, molecular mechanics energy) and a new description of protein conformations by 3-D autocorrelation vectors (3-D ACV). We chose calmodulin (CaM) as a protein model and analysed 23 simulations using different combinations of the four molecular dynamics parameters studied, such as the dielectric constant (epsilon), the heating phase time (H), the thermal bath coupling time (zeta T) and the time step size (delta t). The correctness of the various trajectories generated with different parameter sets was evaluated through geometric analysis and use of a knowledge-based profile method. It is shown that 3-D ACV combined with multivariate statistical analysis provides a convenient way to describe and compare molecular dynamics simulations and constitutes a valuable complementary tool to standard methods. Using these methods, comparison of the various simulations performed on CaM indicated that the best in vacuo parameter set was epsilon = 1 x r, H = 15 ps, zeta T = 0.1 ps and delta t = 1 fs in fairly good agreement with previous less extensive comparisons of molecular dynamics trajectories.

Binding Sites↗