Search PubMed⌕ Search

Biomedical subjects

J Bordas

Publications and source records attributed to J Bordas.

At least 37 records · Page 2Linked to original sources
PubMed1991

Crystallographic analysis of acrosomal bundle from Limulus sperm.

The acrosomal process of Limulus sperm contains a bundle of filaments composed of actin and a 102 kDa protein in a 1:1 molar ratio. The structure of the bundle in true discharge was investigated by electron cryomicroscopy, X-ray scattering and crystallographic image analysis. A bundle can be characterized as a quasi-crystal with continuously varying views along the bundle axis. Each segment of the bundle is found to obey the symmetry of space group P1, with a = b = 147 A, c = 762 A, alpha = 90 degrees, beta = 90.6 degrees, gamma = 120 degrees. A unit cell contains a helical repeat of the filament with a selection rule following that of an actin filament. A 24 A projection map based on the h0l view was reconstructed after averaging 5300 unit cells from six electron images. Filaments in this projection are well separated and clearly display a 21 screw symmetry. This screw symmetry results from the helical parameters of the bundle filament and is found to be a non-crystallographic symmetry element present in the unit cell. Our structural analysis has led to the proposal that the assembly of a stable bundle with a defined maximum diameter can be controlled by the crystallographic packing of the twisted filaments.

Acrosome↗
PubMed1991

Two-dimensional time resolved X-ray diffraction of muscle: recent results.

This report provides a preliminary sketch of the results obtained in a two-dimensional time resolved X-ray diffraction study of "live" frog sartorius muscles undergoing isometric tetani. These results demonstrate the recently developed capability to record time resolved (10 msec time resolution), two-dimensional X-ray diffraction diagrams throughout the cycle of contraction. The correlation between the time courses of the diffraction features in the whole of the diffraction diagram establishes a sequence of structural events, which suggest that during the transition from rest to the plateau of tension and the subsequent recovery, the following sequence of events takes place: a) Following the activation phase, which is best monitored by the increase of intensity on the second actin layer line at 18.0 nm spacing (5), there is the onset of three dimensional disorder due to the filaments losing their axial alignment and the myosin heads rotating azimuthally and moving radially outwards. A set of low-angle layer lines, following the actin based spacings seen in rigor (i.e., at spacings of ca. 36.5-37.5, 24.0 and 18.0 nm) become visible and those at ca. 24.0 and 18.0 nm appear to increase in intensity during this phase with a time course that cannot be determined accurately because of the proximity of the neighbouring first, second and third myosin layer lines and the weakness of these diffraction features. Whether the first of these layer lines increases or not is difficult to ascertain. Moreover, proper account of the loss in crystallinity during the development of tension must be made before the comparisons in intensity between the rest and peak of tension states have any significance. Nevertheless, these features together with the behaviour of the equatorial reflections and the meridional region of the third myosin layer line indicate that a sizeable fraction of the crossbridges may become axially disposed with an actin based periodicity. The formation of this complex does not immediately result in the generation of tension. The labelling of the thin filaments is also reflected in the main actin layer lines at 5.9 and 5.1 nm. b) The tension generating phase is monitored by the intensity changes in the meridional region of the third myosin layer line, which are best explained by a change in the orientation/conformation of the tension bearing crossbridges, (which probably adopt a more perpendicular orientation to the filament axis). c) At the end of stimulation, the crossbridges return to an axial spacing and axial orientation (although not yet azimuthal) similar to the one at rest.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

A comparative study of the supramolecular structure of frog sartorius and dorsal semitendinosus muscle.

This report describes a comparative X-ray diffraction study of the supramolecular structure of frog sartorius and semitendinosus muscles. For sarcomere lengths of 2.7 microns and below the X-ray diffraction diagrams of each muscle type are very similar; the only differences being that the diffraction diagram for semitendinosus muscles exhibit the presence of a broad diffraction band or a cluster of diffraction orders at a spacing of ca. 230.0 nm and, also, they lack a periodicity of ca. 102.0 nm. For sarcomere lengths greater than 2.7 microns disruption of the sarcomere from sartorius muscle occurs as seen by the loss of sampling in the diffraction diagram. The semitendinosus muscle can be stretched to much longer lengths (in excess of 3.0 microns) before a loss of sampling is detected. The data also shows that in the case of the semitendinosus muscle for long sarcomere lengths transverse bands of mass are able to move without retaining a defined distance to either the Z or the M lines. This is not observed in the case of the sartorius muscle. Thus, at resolutions between ca. 3.6 microns and 7.50 nm significant ultrastructural differences between these two muscles are apparent. The data suggest that the ability of these mass bands to move may be responsible for the differences in the development of passive tension exhibited by these two muscles.

Animals↗
PubMed1990

Conformational changes in bacteriophage phi 29 connector prevents DNA-binding activity.

In vitro DNA packaging activity in a defined system derived from bacteriophage phi 29 depends upon the chemical integrity of the connector protein p10. Proteolytic cleavage of p10 rendered the proheads inactive for DNA packaging. A similar treatment on isolated connectors abolished the DNA-binding activity of the native p10, but the general shape and size of the connector was not changed as revealed by electron microscopy. Analytical ultracentrifugation showed that the proteolyzed connectors had a smaller sedimentation coefficient, while amino acid analysis after dialysis of the proteolyzed p10 confirmed the loss of 16 and 19 amino acids from the amino and carboxy termini, respectively. Low angle X-ray scattering revealed that proteolysis was followed by a small decrease in the radius of gyration and a reorganization of the distal domain of the cylindrical inner part of the connector. Characterization of the cleavage sites in the primary sequence allowed us to propose the location of the DNA-binding domain in the connector model.

Amino Acid Sequence↗
PubMed1989

A synchrotron X-ray scattering characterization of purified tubulin and of its expansion induced by mild detergent binding.

This report presents a synchrotron radiation X-ray scattering characterization of calf brain tubulin purified by the modified Weisenberg procedure. The results show that under nonassembly conditions (i.e., in 10 mM sodium phosphate and 0.1 mM GTP, pH 7, buffer) these preparations consist of a uniform population of molecules with a radius of gyration of 3.1 +/- 0.1 nm, which can be interpreted as arising from the native alpha-beta heterodimer. The uniformity in the population persists even at unusually high concentrations of protein. Binding of colchicine or substitution of GTP by GDP does not induce, within the statistical accuracy and resolution range of our measurements, any significant structural modification in soluble tubulin. In assembly buffer [i.e., 10 mM sodium phosphate, 6 mM magnesium chloride, 1 mM [ethylenebis(oxyethylenenitrilo)]tetraacetic acid, 1 mM GTP, and 3.4 M glycerol, pH 6.5], these preparations readily assemble into microtubules upon increasing the temperature from 4 to 37 degrees C. Binding of nondenaturing amphiphiles to soluble tubulin provides a simplified model for tubulin-membrane interactions. The X-ray scattering data show that the radius of gyration of tubulin progressively increases upon binding of the mild detergent sodium deoxycholate, reaching a maximum value of 4.3 +/- 0.1 nm at detergent saturation. The relative increase in the radius of gyration coincides within experimental error with the previously determined relative increase in the frictional coefficient [Andreu, J.M., & Muñoz, J.A. (1986) Biochemistry 25, 5220-5230]. Analysis of these observations suggests that the effect of detergent binding is to induce an isotropic swelling of the protein structure.

Animals↗
PubMed1989

A 220 kDa polypeptide, immunolocalized to epithelial tight junctions, is associated with brain clathrin preparations.

Antibodies were raised in rabbits to highly purified preparations of bovine brain clathrin. The serum stained by immunofluorescence rat liver sections at tight junctions in a pattern that was identical to that previously reported (B. R. Stevenson et al.: J. Cell Biol. 103, 755-766 (1986] in which a monoclonal antibody specific to a 220 kDa (ZO-1) liver tight junction component was used. The serum also stained regions of the cell surface corresponding to the positions of intercellular junctions in confluent MDCK and HepG-2 cell cultures. Analysis of brain clathrin preparations resolved by polyacrylamide gel electrophoresis by immunoblotting with the serum indicated reaction with clathrin heavy and light chains as well as towards a 220 kDa polypeptide that was a minor component. Affinity purification of the serum provided antibodies directed mainly to clathrin light chains and these antibodies, as well as an independent antiserum to clathrin heavy chains, immunofluorescently stained liver tissue and cells in a manner typical of coated membranes/vesicles. These results suggested, by difference, that antibodies to a 220 kDa polypeptide, a minor constituent in brain clathrin preparations, were responsible for staining intercellular tight junctions in epithelia. The 220 kDa polypeptide present in brain clathrin preparations was demonstrated to be immunologically distinct from liver myosin heavy chain as well as erythrocyte and brain ankyrin. Comparison by two-dimensional mapping of the 220 kDa in brain clathrin with the clathrin heavy chain (180 kDa) polypeptide showed they were different proteins, but the 220 kDa polypeptide present in rat liver tight junctions was highly similar to the 220 kDa present in bovine brain clathrin preparations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

[Peripheral bronchopulmonary cancers. Diagnostic efficiency of fibroscopic samples. Prospective study on 561 patients].

The purpose of this french multicentric study was to evaluate the diagnostic accuracy of samples collected by fibroscopy in peripheral lung cancer with normal endoscopy. Five hundred and sixty-one patients entered the study; a tumour had been diagnosed in 350 of them (62 p. 100). Among these 350 patients, 147 were examined with the help of a light-amplifier screen, and a positive diagnosis was made in 97 (66 p. 100). Guided sample collection in the pathological area (biopsy, brushing, transcatheter aspiration) proved much more rewarding than unguided sample collection (biopsy of the bronchus, simple aspiration or cytology of 3-day sputum): 45 p. 100 positive results versus 18 p. 100 (P less than 0.001). However, sputum cytology still had good diagnostic value since it provided by itself the diagnosis in 14 p. 100 of the cases. Results were significantly inferior in tumours less than 3 cm in diameter.

Adult↗
PubMed1987

Tubulin oligomers and microtubule assembly studied by time-resolved X-ray scattering: separation of prenucleation and nucleation events.

This paper describes a time-resolved X-ray scattering study of microtubule assembly by synchrotron radiation. The method is complementary to light scattering but allows a better distinction between oligomeric and polymeric assembly states. With an improved rapid temperature jump device, it is shown that temperature-induced microtubule assembly is preceded by prenucleation and nucleation events involving oligomers of tubulin, in analogy with earlier results from near-equilibrium temperature scans. In general, the two phases closely overlap, but in certain conditions they can be observed separately. The prenucleation events seen by X-rays can be described as a rapid temperature-dependent equilibrium, with ring oligomers dissociating into smaller oligomers and subunits at elevated temperature. Different solution conditions affect mainly the time lag between the prenucleation and nucleation phases; this in turn determines the apparent magnitude of the prenucleation steps. By contrast, the temperature dependence of the equilibrium between the prenucleation oligomers shows little influence on solution conditions. The results suggest that the ring-forming and tubule-forming assembly modes of tubulin are governed by different interactions between subunits, although they may be based on a pool of similar intermediates.

Hydrogen-Ion Concentration↗
PubMed1987

Synchrotron x-ray diffraction studies of actin structure during polymerization.

Synchrotron x-ray diffraction was used to identify the oligomers that formed during the earliest stages of actin polymerization. Solution diffraction patterns from G-actin (monomer) and from F-actin (polymer) contain information about the size and shape of actin monomers and the length, width, and subunit organization of filaments. Comparison of patterns collected during polymerization reveals an increase in scatter at spacings greater than 9.0 nm; formation of scattering bands at 5.4,4.9, and 3.4 nm; formation of a scattering minimum at 6.5 nm; and the presence of an isosbestic point at 9.0 nm. These scattering bands arise from the formation of, and organization of subunits in, filaments. At various actin concentrations (0.37-5 mg/ml), the change in scatter in these regions follows simple exponential kinetics with no detectable lag. Our analysis of the x-ray patterns shows that by 0.4 sec after mixing, most of the actin has formed dimers, which then rapidly incorporate into oligomers. At 4 mg/ml the early oligomers increase in length to greater than 30.0 nm within 10 sec. These results suggest that under our conditions actin molecules condense into filaments without the rate-limiting formation of nuclei.

Actins↗
PubMed1987

X-ray diffraction evidence for the existence of 102.0- and 230.0-nm transverse periodicities in striated muscle.

Synchrotron radiation techniques have enabled us to record meridional x-ray diffraction patterns from frog sartorius muscle at resolutions ranging from approximately 2,800 to 38 nm (i.e., overlapping with the optical microscope and the region normally accessible with low angle diffraction cameras). These diffraction patterns represent the transform of the low resolution structure of muscle projected on the sarcomere axis and sampled by its repeat. Altering the sarcomere length results in the sampling of different parts of this transform, which induces changes in the positions and the integrated intensities of the diffraction maxima. This effect has been used to determine the transform of the mass projection on the muscle axis in a quasicontinuous fashion. The results reveal the existence of maxima arising from long-range periodicities in the structure. Determination of the zeroes in the transforms has been used to obtain phase information from which electron density maps have been calculated. The x-ray diffraction diagrams and the resulting electron density maps show the existence of a series of mass bands, disposed transversely to the sarcomere axis and distributed at regular intervals. A set of these transverse structures is associated with thin filaments, and their 102.0-nm repeat suggests a close structural relationship with their known molecular components. A second set, spaced by approximately 230.0 nm, is also present; from diffraction theory one has to conclude that this repeat simultaneously exists in thick and thin filament regions.

Animals↗
PubMed1986

The superstructure of chromatin and its condensation mechanism. I. Synchrotron radiation X-ray scattering results.

Synchroton radiation X-ray scattering experiments have been performed on chicken erythrocyte chromatin fibres over a wide range of ionic conditions and on various states of the fibres (i.e. "native" in solution, in gels and in whole nuclei; chromatin depleted of the H1 (H5) histones and chromatin with bound ethidium bromide). A correlation between the results obtained with the various chromatin preparations provides evidence for a model according to which at low ionic strength the chromatin fibre already possesses a helical superstructure, with a diameter comparable to that of condensed chromatin, held together by the H1(H5) histone. The most significant structural modification undergone upon an increase of the ionic strength is a reduction of the helix pitch, this leads to condensation in a manner similar to the folding of an accordion. The details of this process depend on whether monovalent or divalent cations are used to raise the ionic strength, the latter producing a much higher degree of condensation. Measurements of the relative increase of the mass per unit length indicate that the most condensed state is a helical structure with a pitch around 3.0-4.0 nm. In this paper we give a detailed presentation of the experimental evidence obtained from static and time-resolved scattering experiments, which led to this model.

Animals↗
PubMed1986

The superstructure of chromatin and its condensation mechanism. II. Theoretical analysis of the X-ray scattering patterns and model calculations.

Model calculations on the superstructure of uncondensed and condensed chromatin are presented. It is found that agreement between the calculated X-ray solution scattering patterns and the experimental observations can be reached with the assumptions that: a) The uncondensed chromatin fibre in solution has a helix-like structure, with a pitch of ca. 33.0 nm, a helical diameter of ca. 20.0 nm and 2.75-3.25 nucleosomes per turn. b) The most condensed state of the chromatin fibre in solution is best represented by a helix-like structure with ca. 2.56 nucleosomes per turn, a pitch of ca. 3.0 nm and a helical diameter of ca. 27.0 nm.

Animals↗
PubMed1985

Time-resolved X-ray scattering study of actin polymerization from profilactin.

The polymerization of actin in solutions of purified calf spleen actin or profilactin (1-10 mg . ml-1) was followed by synchrotron radiation X-ray solution scattering. At the concentration used, polymerization of actin from profilactin or actin occurs without any lag phase. It is shown by a combination of solution scattering, model calculations and electron microscopy that contrary to the conclusions from previous viscometry studies, filaments form without any lag phase in profilactin solution but aggregate in bundles or networks. This phenomenon is independent of the method used to induce polymerization: slow temperature increase, temperature jump in the presence of polymerizing salts or fast mixing with salt. This aggregation explains the lower final viscosity levels, as compared to actin solutions, observed during the polymerization of actin from profilactin.

Actins↗
PubMed1985

Synchrotron radiation x-ray scattering in the early stages of in vitro collagen fibril formation.

The time course of in vitro collagen fibril formation was monitored by synchrotron radiation x-ray scattering. Collagen polymerization was induced by a temperature jump from 4 degrees C to 32 degrees C and the solution scattering pattern was recorded continuously with a time resolution of a few seconds. The scattered intensity increased as soon as the final temperature was attained, without discernible lag phase, when the collagen concentration was about 0.56 mg/ml, whereas turbidimetric measurements revealed a lag phase of ca. 2.5 min at 1.05 mg/ml. A direct correlation was found between the temperature and both the rate of formation and the total amount of early aggregates. The formation of these aggregates was only partially reversed by lowering the temperature, except when the collagen had been prevented from forming Schiff base-mediated intermolecular crosslinks by sodium borohydride reduction. In this case, formation of aggregates was completely reversible. We conclude that the aggregates that appear to correspond to the subfibrils proposed on the basis of independent methods are formed and simultaneously crosslinked in the early phases of in vitro collagen self-assembly.

Animals↗
PubMed1984

Chromatin superstructure: synchrotron radiation X-ray scattering study on solutions and gels.

X-ray small angle scattering patterns of solutions and gels of native chicken erythrocyte chromatin and chromatin depleted of H5 histones have been measured under several ionic conditions using synchrotron radiation. Features of the patterns are interpreted as resulting from a superstructure with an outer diameter of about 300A which is already present in uncondensed nucleofilaments. This superstructure which is shown to be maintained by the H5 histones also explains the rapid condensation of the nucleofilaments in higher ionic strengths.

Animals↗
PubMed1983

[Effect of Biostim on broncho-pulmonary cellular defense elements. Preliminary results of a study on broncho-alveolar lavage].

The purpose of our investigation is to evaluate the action of C 1740 (Biostim tablets) on bronchopulmonary cellular defense mechanisms through the study of bronchoalveolar lavage samples. C 1740 is a non-specific immuno-stimulant whose effectiveness in preventing suprainfection of chronic bronchopathies has been demonstrated in clinical studies. Ten patients (mean age 51.5 years; range 37 to 68) with a history of recurrent bronchial infections, but currently free of such disease, were randomly divided into two groups. Five constituted the control group and five were given Biostim (8 mg/day) for 15 days. In both groups a bronchoalveolar lavage with cytological and biochemical studies was done in each patient, at identical intervals (DO and D16). Despite technical difficulties due to bronchial obstruction, which partly hindered the study, significant differences were found between the two groups, showing quantitative and qualitative cellular changes in patients under Biostim, with increased cell, especially lymphocyte, counts. This may be the result of stimulation by Biostim of immunological reactions normally found during the course of bronchopulmonary infections and which undoubtedly play a part in preventing new episodes. These preliminary results need confirmation but throw light on one of Biostim's possible mechanisms of action upon immunological defenses.

Adult↗