Search PubMed⌕ Search

Biomedical subjects

H Labischinski

Publications and source records attributed to H Labischinski.

At least 55 records · Page 3Linked to original sources
PubMed1990

Architecture of bacterial lipid A in solution. A neutron small-angle scattering study.

The phase structure of isolated bacterial lipid A, the lipid anchor of the lipopolysaccharides of the outer membrane of Gram-negative bacteria, has been investigated by neutron small-angle scattering. The shape of the scattering curves obtained at different H2O/2H2O ratios revealed a lamellar organisation of the lipid A at neutral pH both above and below its main phase temperature (approximately 40-45 degrees C). Analysis of the scattering curves and interpretation of the corresponding thickness distance distribution functions of the lamellar aggregates led to a model in which the lipid A molecules form a bilayer of about 5 nm in thickness. This value for the thickness of the bilayer, as well as the neutron-scattering density profile across the bilayer, can be explained by a molecular model which shows interdigitation of the fatty acid chains of the lipid A.

Hydrogen-Ion Concentration↗
PubMed1990

Penicillin-induced changes in the cell wall composition of Staphylococcus aureus before the onset of bacteriolysis.

To analyze if chemical cell wall alterations contribute to penicillin-induced bacteriolysis, changes in the amount, stability, and chemical composition of staphylococcal cell walls were investigated. All analyses were performed before onset of bacteriolysis i.e. during the first 60 min following addition of different penicillin G doses. Only a slight reduction of the amount of cell wall material incorporated after penicillin addition at the optimal lytic concentration was observed as compared to control cells. However, the presence of higher penicillin G concentrations reduced the incorporation of wall material progressively without bacteriolysis. Losses of wall material during isolation of dodecylsulfate insoluble cell walls were monitored to assess the stability of the wall material following penicillin addition. Wall material grown at the lytic penicillin concentration was least stable but about 30% of the newly incorporated wall material withstood even the harsh conditions of mechanical breakage and dodecylsulfate treatment. Dodecylsulfate insoluble cell walls were used for chemical analyses. While peptidoglycan chain length was unaffected in the presence of penicillin, other wall parameters were considerably altered: peptide cross-linking was reduced in the wall material synthesized after addition of penicillin; reductions from approx. 85% in controls to about 60% were similar for lytic and also for very high penicillin concentrations leading to nonlytic death. O-acetylation was also reduced after treatment with penicillin; this effect paralleled the occurrence of subsequent bacteriolysis at different drug concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylation↗
PubMed1989

The tetrameric form of ribosomal protein L7/L12 from Escherichia coli.

A tetrameric form of the ribosomal protein L7/L12 has been prepared and its structure studied by using hydrodynamic methods, photon correlation spectroscopy, and small angle x-ray scattering. The tetrameric nature of the protein preparation is confirmed by three independent determinations of its molecular weight, with analysis of accurate sedimentation equilibrium data giving the most reliable estimate. The species has a Stokes radius of 4.0 +/- 0.1 nm and an absolute frictional ratio of 1.7. Taken together, the hydrodynamic measurements suggest the possibility of a flat structure, and this is consistent with the x-ray scattering results. The molecule has a radius of gyration of 3.6 +/- 0.05 nm and a maximum dimension of 11-12 nm. A geometric model consisting of four elongated monomers, arranged in a plane, is proposed.

Bacterial Proteins↗
PubMed1989

Comparative X-ray and Fourier-transform-infrared investigations of conformational properties of bacterial and synthetic lipid A of Escherichia coli and Salmonella minnesota as well as partial structures and analogues thereof.

By using the X-ray and infrared spectroscopic characteristics of various synthetic analogues and partial structures of lipid A in the dried state, a comparison of these compounds with their natural counterparts was undertaken. As judged by their X-ray diffraction and infrared spectroscopic features, the compounds tested could be divided into two main groups. The first group covered those samples synthesized in accordance with a previously assumed structure, while those synthesized in accordance with present knowledge on the lipid-A primary structure formed the second group. Members of the first group were characterized by a liquid-like, alpha-type arrangement of their fatty acyl chains in a non-lamellar supramolecular structure, while all members of the second group formed bilayered phases with a much more ordered, beta-type conformation of their fatty acyl chains. Synthetic Escherichia coli-type lipid A (compound 506), proved to be essentially identical to its natural counterpart with respect to those conformational properties accessible by our methods. The synthetic hepta-acyl species of Salmonella minnesota lipid A (compound 516) revealed an unexpected conformational behaviour, whereby a fatty-acyl-chain packing could be detected which was different from the hexagonal arrangement found for all other compounds of the second group.

Escherichia coli↗
PubMed1989

Onset of penicillin-induced bacteriolysis in staphylococci is cell cycle dependent.

Synchronously growing staphylococci were treated with "lytic" concentrations of penicillin at different stages of their division cycle. Coulter Counter measurements and light microscopy were used to determine the onset of bacteriolysis. Independent of the stage of the division cycle at which penicillin was added, (i) the cells were always able to perform the next cell division; (ii) the following division, however, did not take place; and (iii) instead, at this time, when the onset of the subsequent cell separation was observed in control cultures, lysis of the penicillin-treated cells occurred. These results support a recent model (P. Giesbrecht, H. Labischinski, and J. Wecke, Arch. Microbiol. 141:315-324, 1985) explaining penicillin-induced bacteriolysis of staphylococci as the result of a special morphogenetic mistake during cross wall formation.

Cell Cycle↗
PubMed1987

Investigations into the polymorphism of lipid A from lipopolysaccharides of Escherichia coli and Salmonella minnesota by Fourier-transform infrared spectroscopy.

The polymorphism of lipid A, the endotoxic principle of the lipopolysaccharides of gram-negative bacteria, has been investigated in the fully hydrated state at temperatures between 5 degrees and 58 degrees C via Fourier-transform infrared spectroscopy. These measurements were supplemented by X-ray diffraction, fluorescence intensity techniques and differential thermal analysis. Up to three distinct phase transitions could be detected, with the main transition temperatures lying at approximately 41 degrees, 46 degrees, 44 degrees and 47 degrees C for Escherichia coli lipid A, Salmonella minnesota lipid A, and the synthetic lipid A compounds 506 and 516, respectively. 4'-Monophosphoryl-lipid A samples exhibited their main transition temperatures at considerably higher temperatures (about 52 degrees C for E. coli lipid A). The analysis of greater than CH2 stretching absorption bands as well as the wide-angle scattering behaviour of the lipid A samples showed that the main transition apparently involved the completion of hydrocarbon chain melting of lipid A, as typically observed for phospholipids. However, the phase transition behaviour was found to be much more complex than that usually observed for model phospholipid systems. Even below the main transition temperature, considerable amounts of the methylene segments of the acyl chains of lipid A were found to assume gauche conformations. These conformational changes might be related to the occurrence of up to two further transitions located at about 22 degrees, 30 degrees, 27 degrees and 25.5 degrees C (first transition) and at about 34 degrees, 42 degrees, 38.5 degrees and 40.5 degrees C (second transition) for E. coli lipid A, S. minnesota lipid A and the synthetic lipid A compounds 506 and 516, respectively. Furthermore, by the analysis of some characteristic infrared absorption bands related to the hydrophilic backbone, it could be demonstrated that the temperature-induced conformational changes occurring within the hydrocarbon chains were constantly and simultaneously accompanied by detectable rearrangements within the interfacial region and the polar head group of lipid A. The following conclusions were drawn: Up to about 30 degrees C the lipid A assemblies were supposed to adopt virtually bilayered, true lamellar arrangements, as revealed by the analysis of greater than CH2 scissoring vibrations and X-ray diffraction pattern. However, as indicated by fluorometric techniques, no stable closed vesicles seemed to be formed even under these conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Calorimetry↗
PubMed1986

Heavy riboflavin synthase from Bacillus subtilis. Particle dimensions, crystal packing and molecular symmetry.

Heavy riboflavin synthase from Bacillus subtilis is an enzyme complex consisting of approximately three alpha-subunits (Mr 23.5 X 10(3)) and 60 beta-subunits (Mr 16 X 10(3)). The enzyme has been crystallized from phosphate buffer in a hexagonal crystal modification that belongs to space group P6(3)22. The asymmetric unit of the crystal cell contains ten beta-subunits. The structure of this unusual 10(6) Mr protein has been studied by small-angle X-ray scattering, electron microscopy of three-dimensional crystals, and crystallographic methods. The scattering curves can be interpreted in terms of a hollow sphere model with a ratio of inner and outer radius of 0.3:1. A diameter of 168 A was estimated from the scattering curves, in close agreement with electron microscopic studies. An aggregate with the stoichiometry beta 60, which was obtained by ligand-driven reaggregation of isolated beta-subunits, showed similar shape and dimensions, but a larger value for the ratio Ri/Ra. Electron micrographs of freeze-etched enzyme crystals showed approximately spherical molecules, which were arranged in hexagonal layers. The lattice constants found from the micrographs are in good agreement with the values derived from X-ray diffraction data. Rotation function calculations in Patterson space showed a set of peaks for 2-fold, 3-fold and 5-fold local rotation axes, accurately consistent with icosahedral symmetry and with the particle orientation A shown in the Appendix. The crystal packing can be described as follows: enzyme particles with icosahedral symmetry (point group 532) are located at points 32 of the hexagonal cell, corresponding to positions (0, 0, 0) and (0, 0, 1/2) on the 6-fold screw axes. From the data reported, it may be concluded that the enzyme structure can be described as an icosahedral capsid of 60 beta-subunits with the triangulation number T = 1. The alpha-subunits are located in the central core space of the capsid, but their spatial orientation is incompletely understood.

Bacillus subtilis↗
PubMed1985

Neither an enhancement of autolytic wall degradation nor an inhibition of the incorporation of cell wall material are pre-requisites for penicillin-induced bacteriolysis in staphylococci.

In contrast to what has been postulated, penicillin G at its optimal lytic concentration of 0.1 microgram per ml did not lead to a detectable activation of autolytic wall processes in staphylococci in terms of the release of uniformly labelled wall fragments from cells pretreated with the drug for 1 h. Rather a considerable inhibition of this release was observed. A similarly profound inhibition of the release of peptidoglycan fragments occurred when staphylococci pretreated for 1 h with 0.1 microgram penicillin per ml acted as a source of crude autolysins on peptidoglycan isolated from labelled normal cells of the same strain. This clearly demonstrated that the overall inhibition of autolytic wall processes caused by penicillin was mainly due to a decreased total autolysin action rather than to an altered wall structure. Furthermore, no substantial penicillin-induced inhibition of the incorporation of 14C-N-acetylglucosamine into the staphylococcal wall could be observed before bacteriolysis started, i.e., approximately during the first 80 min of penicillin action. These results are not consistent with any of the models hitherto proposed for the action of penicillin.

Bacteriolysis↗
PubMed1985

A special morphogenetic wall defect and the subsequent activity of "murosomes" as the very reason for penicillin-induced bacteriolysis in staphylococci.

The actual reason for the penicillin-induced bacteriolysis of staphylococci was shown to be the "punching" of one or a few minute holes into the peripheral cell wall at predictable sites. These perforations were the result of the lytic activity of novel, extraplasmatic vesicular structures, located exclusively within the bacterial wall material, which we have named "murosomes". In untreated staphylococci the punching of holes into the peripheral wall is a normal process which follows cross wall completion and represents the first visible step of cell separation. Under penicillin, however, analogous holes are punched by the murosomes at sites of presumptive cell separation even if no sufficient cross wall material had been assembled before at this site (but had rather been deposited at other sites). Consequently, because of the internal pressure of the protoplast, lytic death is the inevitable result of this perforation of the protective peripheral wall. Hence, the real mechanism of penicillin-induced bacteriolysis in staphylococci is considered to be mainly the result of a special morphogenetic wall defect: bacteriolysis is taking place regularly when a cell separation process is no longer preceeded by sufficient cross wall assembly at the correct place. However, hypotheses which are based purely on some variations of overall biochemical processes like total wall enzyme activities or total wall synthesis are not regarded to be sufficient to explain this type of lytic death.

Bacteriolysis↗
PubMed1985

High state of order of isolated bacterial lipopolysaccharide and its possible contribution to the permeation barrier property of the outer membrane.

The conformational properties of the isolated S form of Salmonella sp. lipopolysaccharide (LPS), of Re mutant LPS, and of free lipid A were investigated by using X-ray diffraction and conformational energy calculations. The data obtained showed that LPS in a dried, in a hydrated, and probably also in an aqueous dispersion state is capable of forming bilayered lamellar arrangements similar to phospholipids. From the bilayer packing periodicities, a geometrical model of the extensions of the LPS regions lipid A, 2-keto-3-deoxyoctulosonic acid, and O-specific chain along the membrane normal could be calculated. Furthermore, the lipid A component was found to assume a remarkably high ordered conformation: its fatty acid chains were tightly packed in a dense hexagonal lattice with a center-to-center distance of 0.49 nm. The hydrophilic backbone of lipid A showed a strong tendency to form domains in the membrane, resulting in a more or less parallel arrangement of lipid A units. According to model calculations, the hydrophilic backbone of lipid A appears to be oriented approximately 45 degrees to the membrane surface, which would lead to a shed roof-like appearance of the surface structure in the indentations of which the 2-keto-3-deoxyoctulosonic acid moiety would fit. In contrast, the O-specific chains assume a low ordered, heavily coiled conformation. Comparison of these structural properties with those known for natural phospholipids in biological membranes indicates that the high state of order of the lipid A portion of LPS might be an important factor in the structural role and permeation barrier functions of LPS in the outer membrane of gram-negative bacteria.

Bacteria↗
PubMed1984

A new proposal for the primary and secondary structure of the glycan moiety of pseudomurein. Conformational energy calculations on the glycan strands with talosaminuronic acid in 1C conformation and comparison with murein.

Using the method of conformational energy calculations, favoured conformations of a pseudomurein sugar strand built up from beta 1,3-linked N-acetyl-D-glucosamine and N-acetyl-L-talosaminuronic acid were obtained. Such a completely beta 1,3-linked polysaccharide primary structure, although contrasting with the originally proposed alternating beta 1,3-alpha 1,3-linked structure [König, H., Kandler, O., Jensen, M. and Rietschel, E. Th. (1983) Hoppe-Seyler's Z. Physiol. Chem. 364, 627-636] would be in agreement with all experimental data hitherto known. Starting from an analysis of favoured conformations of the monosaccharide building blocks and those obtained for disaccharide parts, the favoured helical conformations of the complete polysaccharide chains could be explored. Our completely beta 1,3-linked chain could adopt two types of conformation: extended and hollow; the latter was discarded as unsuitable for cell wall assembly. The extended conformation type was shown to exhibit a remarkable similarity if compared to the secondary structures accessible to murein-type polysaccharide chains. In contrast to the conformations accessible for the beta 1,3-alpha 1,3-linked primary structure, the new hypothetical pseudomurein structure was found to be more extended, possessed a flexible peptide attachment site at every second sugar residue and led to an orientation of consecutive peptide attachment sites analogous to the data known for murein-type chains. From the two possibilities compatible with the experimental data available, the completely beta 1,3-linked sugar strand structure could well be realized in the native pseudomurein network of methanobacteria. In this case the hypothesis for a similar three-dimensional architecture for murein and pseudomurein would be supported.

Carbohydrate Conformation↗
PubMed1984

Study of the Zn-containing DD-carboxypeptidase of Streptomyces albus G by small-angle X-ray scattering in solution.

Study of the Zn2+-containing D-alanyl-D-alanine-cleaving carboxypeptidase of Streptomyces albus G by small-angle X-ray scattering in solution yielded the following molecular parameters: radius of gyration R = 1.82 +/- 0.05 nm; largest diameter D = 5.9 +/- 0.2 nm; relative molecular mass Mr = 17000 +/- 2000; volume V approximately equal to 35 +/- 2 nm3; degree of hydration: 0.25 +/- 0.02 g water/g protein. By reference to theoretical scattering curves of rigid triaxial homogeneous bodies, a model which fits all experimental data is an elliptical cylinder. Such a model is compatible with that observed in the crystal structure. At those high concentrations necessary to form inactive enzyme-ligand associations the non-competitive beta-lactam inhibitors, cephalothin and cephalosporin C, drastically altered the scattering behaviour of the protein.

Carboxypeptidases↗
PubMed1982

Infrared spectroscopy, a tool for probing bacterial peptidoglycan. Potentialities of infrared spectroscopy for cell wall analytical studies and rejection of models based on crystalline chitin.

Infrared spectroscopic measurements are used to obtain insights into the three-dimensional architecture of peptidoglycan (murein), the rigid component of almost all bacterial cell walls. The infrared spectra of various types of peptidoglycans (including all chemotypes and examples of the so called A and B groups) were compared to each other and to those obtained from crystalline chitin. All peptidoglycans investigated exhibited very similar infrared spectra. In particular the conformationally sensitive amide A, I and II absorption bands were found to be constantly centered around 3300 cm-1, 1657 cm-1 and 1534 cm-1 respectively; furthermore, the spectral region between 1200 cm-1 and 800 cm-1, characterized by several strong absorption bands connected to complex sugar ring modes, proved to be remarkably uniform. Additionally the infrared spectra remained significantly constant between -175 degrees C and + 75 degrees C and turned out to be rather independent of sample preparation (solvent replacement, freeze-drying and film producing). An analysis of band half-widths revealed no high crystalline state of order of peptidoglycan. On the basis of band positions and half-widths of amide bands, regular conformations like alpha helices of beta pleated sheets could be excluded. Several distinctive, fingerprint-like spectral features of the various murein samples permitted a facile identification of individual peptidoglycans. Moreover, infrared spectroscopy seems to be very promising as an analytical tool, e.g. for tracing variations of cell wall structure, detecting conformational changes and estimating crosslinking indices in a quick and simple way. The comparative analysis of amide band positions and band half-widths yielded substantial differences between infrared spectra of chitin and murein, thus rejecting previous models based on the assumption of a nearly crystalline chitin-like structure of the glycan chains of murein.

Bacteria↗
PubMed1979

Protein S1 from Escherichia coli ribosomes: an improved isolation procedure and shape determination by small-angle X-ray scattering.

Ribosomal protein S1 from Escherichia coli was studied in solution by small-angle X-ray scattering and the following parameters were obtained. The radius of gyration R = 8.0 +/- 0.2 nm; largest diameter D = 28 nm; molecular weight = (8--9) x 10(4). The data also yielded (with the assumption of a rigid particle with almost constant electron density) two radii of gyration of cross-section Rq1 = 2.5 +/- 0.1 nm and Rq2 = 1.05 +/- 0.05 nm and molecular volume = 140 nm3. The experimental scattering curve of S1 was compared with the theoretical scattering curves for several rigid triaxial homogeneous bodies and the closest fit was given by that of a flat elliptical cylinder with the dimensions of 4.5 nm and 0.88 nm for the two semiaxes and 26.5 nm for height. The results from the present X-ray scattering studies and those from limited proteolytic digestion of protein S1 [J. Mol. Biol. 127, 41--54, (1979)] support the notion that the structure of protein S1 is organized into two distinct subdomains within its elongated overall shape. Protein S1 was purified for this study by an efficient procedure which yielded 12 mg S1/g ribosomes. The isolated protein was fully active in functional tests both before and after X-ray irradiation.

Bacterial Proteins↗
PubMed1979

Conformational energy calculation on the peptide part of murein.

Conformational energy calculations have been carried out on N-acetyl-L-alanyl-D-gamma-glutamyl-L-lysyl-D-alanyl-D-alanine as a model of the peptide moiety of peptidoglycan. Although many conformations were of comparable energy, particular favoured conformations were selected by assuming conformational similarity between the pentapeptide and the tetrapeptide found during biosynthesis subsequent to the cross-linking of the peptide chains in murein. The common feature of these conformations, which include the global minimum of the pentapeptide, is a ring-shaped backbone. The global minimum is stabilised by a hydrogen bond between the -NH group of L-alanine and the -CO group of the penultimate D-alanine. The distance between the D-lactyl group and the side-chain of the diamino acid is about 1.5 nm. The ring-like structures will accomodate chemical modifications that have been observed in peptidoglycan. The present ring-like structure differs considerably from the models proposed as yet. Energetically beta-pleated sheet conformations and a flat 2.2(7) helical structure are not favoured. Furthermore, an alpha helix cannot occur. The suggested new model exhibits no significant relationship to the solid state conformation of beta-lactam antibiotics.

Amino Acid Sequence↗