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Biomedical subjects

U Aebi

Publications and source records attributed to U Aebi.

At least 181 records · Page 10Linked to original sources
PubMed1977

New method for localizing proteins in periodic structures: Fab fragment labeling combined with image processing of electron micrographs.

Fab fragments prepared from antisera directed against purified bacteriophage T4 structural proteins and head-related structures were used to label proteins on the surface of T-even giant phage capsids. Optically filtered electron micrographs of the Fab-labeled capsids reveal both the location of specific proteins within the capsomeres and differing conformational states of the protein subunits. We describe parameters affecting the utility of this technique for the study of molecular organization and protein conformation in periodic biological structures.

Antibodies, Viral↗
PubMed1976

Comparison of the structural and chemical composition of giant T-even phage heads.

A study has been made of the structure of the capsids of T4D giant phage produced from mutants in gene 23 and temperature-sensitive mutants in gene 24, and T4D and T2L giant phage formed by the addition of L-canavanine followed by an Larginine chase in the growth medium. All the giant phage capsids have been shown to be built according to the same geometrical architecture. This consists of a near-hexagonal surface net, lattice constant 129.5 A, folded into a left-handed T = 13 prolate icosahedron elongated along one of its fivefold symmetry axes. Their only apparent difference from wild-type T-even phage capsids is their abnormally elongated tubular part. A comparison of the capsomere morphologies and protein compositions of the giant phage capsids showed that all T4D giants are identical but differ from T2L: The T4D capsomere has a complex (6 + 6 + 1)-type morphology, whereas the T2L has a simple 6-type. T2L phage, however, lack two capsid proteins, "soc" and "hoc", present in T4D. The difference in capsomere morphology can therefore be related to the difference in the protein compositions of these two phage. Possible differences between the initiation and means of length regulation of giant phage heads and the aberrant polyheads are discussed.

Capsid↗
PubMed1976

[Early treatment of cerebral movement disorders: findings among 50 school children].

It is difficult to assess objectively the effectiveness of treating children with cerebral palsy during the first year of life. 50 pupils with cerebral palsy were selected for handicap and intelligence and carefully examined. All children were treated with the neurodevelopmental technique of BOBATH, 22 of them within the first year of life, 28 thereafter. The examination in school age showed differences between the two groups. When treatment is commenced before nine months of age, children with spastic diplegia resulting from premature birth are unlikely to require special schooling for reasons of their physical handicap. After early treatment, patients with severe neuromuscular dysfunction in early life frequently display disturbances of a predominantly ataxic nature when reaching school age. Spasticity appears to respond well and athetosis less favorably to early treatment. More severe brain damage in the early treated children is possibly indicated by the higher incidence of epilepsy. Pupils who were treated early show significantly fewer behavioural disturbances, with the exception of cases where symbiotic neurosis in the mother is present. This is important for the development of the personality and the individual capacity of integration.

Cerebral Palsy↗
PubMedDate not supplied

Direct in situ structural analysis of recombinant outer membrane porins expressed in an OmpA-deficient mutant Escherichia coli strain.

An OmpA-deficient mutant of an OmpF/OmpC-free Escherichia coli B strain was selected using phage K3. The mutant strain was characterized by SDS-gel electrophoresis, immunoblotting, and electron microscopy. All major outer membrane proteins, including OmpA, were absent. This strain was then transformed with the plasmid pMY222 encoding the K12 OmpF porin or with pBlue-script-derived plasmids, encoding the porins OmpC, PhoE, and maltoporin, respectively. Following SDS extraction of outer membrane sacculi from strains expressing individual porins, crystalline porin arrays that allowed in situ structural analysis to be performed were observed. Furthermore, the absence of endogenous major outer membrane proteins facilitated the purification of native porin-lipopolysaccharide complexes, the functionally active channels, from the sacculi of transformed strains.

Bacterial Outer Membrane Proteins↗
PubMedDate not supplied

Native talin is a dumbbell-shaped homodimer when it interacts with actin.

Electron microscopy of glycerol-sprayed and rotary metal-shadowed talin from human platelets reveals a dumbbell-shaped molecule with an average length of approximately 51 nm. Analytical ultracentrifugation of native talin yields a single molecular species with an apparent molecular mass of 412 (+/- 28.6) kDa and a sedimentation coefficient of S20w = 11.2. Chemical cross-linking with glutaraldehyde (GA) and corresponding SDS-PAGE analysis show that the monomer band of talin can be quantitatively converted to a dimer band at GA concentrations > or = 0.45%, indicating that there is no significant amount of monomer present in solution. These structural and biophysical data are compatible with native talin being an antiparallel homodimer. Length measurements and viscometric and fluorescent assays of actin filaments polymerized in the presence of native talin and of covalently cross-linked talin dimers all yield similar effects: namely, increased nucleation and polymerization rates and an overall reduction of actin filament length. Hence, we conclude that talin in its native biological state is a dimer when promoting nucleation of actin filaments.

Actins↗
PubMedDate not supplied

Structural and physicochemical analysis of the contractile MM phage tail and comparison with the bacteriophage T4 tail.

The three-dimensional (3-D) structure of the bacteriophage MM extended tail has been determined from electron micrographs of negatively stained specimens and compared with 3-D models of coprocessed extended bacteriophage T4 tails. Accordingly, the phage MM extended tail exhibits an axial repeat of 3.8 nm and can be indexed according to the integer helical selection rule l = -3n + 7m (n = 6n') compared to 4.1 nm and l = -2n + 7m (n = 6n') for the T4 phage tail. Compared to the T4 tail sheath, which reveals a stacked-disk-like appearance, the MM tail exhibits a more open structure, yielding an arrow-head-like appearance. Although the phage MM extended tail sheath is more stable than the T4 tail sheath under low-ionic-strength conditions, various chemical treatments of the MM tail sheath revealed responses, notably disassembly and contraction, similar to those previously described for the T4 tail sheath. Extended tails and their structural components contained in phage lysates or prepared by chemical degradation were compared in the EM, and the mass-per-length values of extended tails and tail tubes were determined by quantitative scanning transmission electron microscopy and compared to the corresponding values computed from the respective 3-D mass density maps. Accordingly, masses of 111 and 135 kDa/nm were obtained for the MM and T4 phage tail sheaths, respectively, with the corresponding tail tubes calculated at 19.3 and 25.5 kDa/nm, respectively. Although negative staining and freeze drying/metal shadowing of the two tails revealed different extended tail sheath structures, freeze-dried/metal-shadowed specimens of their contracted tails revealed very similar 6-fold symmetric axial repeats, with the subunits arranged on a pseudo-12-fold symmetric surface lattice following the integer helical selection rule l = n + 11m. In both cases tail contraction started at the baseplate and propagated headward as a wave forming a contraction gradient with a sharp boundary.

Bacteriophage T4↗
PubMedDate not supplied

In vitro maturation of prehead-like bacteriophage T4 polyheads: structural changes accompanying proteolytic cleavage and lattice expansion.

We have studied cleavage and expansion of the major T4 phage capsid protein gp23 (56 kDa) using polyheads, an aberrant, polymorphic tubular variant of bacteriophage T4D, as a model system. In a first step, we have cleaved the 65-amino-acid-long amino-terminal "delta piece" by limited proteolysis with Staphylococcus aureus V8 protease (type XVII) at exactly the same position, i.e., between residues 65 and 66, at which the phage-coded T4Ppase cleaves, to yield mature gp23* (48.7 kDa) without significantly affecting a second potential cleavage site between amino acids 142 and 143. Negatively stained preparations of thus cleaved polyheads revealed a near-hexagonal lattice with a 11.2-nm lattice constant. One-sided correlation averages of these cleaved/unexpanded polyheads yielded capsomeres that were rounder than those of prehead-like (i.e., uncleaved) control polyheads, with distinct trimers of mass (specifically, trimers of delta pieces in the area where three protomers are shared among three different capsomeres) removed, as revealed by difference maps computed from the correlation averages. Quantitative expansion of the 11.2-nm near-hexagonal lattice into the 13-nm near-hexagonal lattice characteristic of mature phage heads could be induced by pelleting the cleaved/unexpanded polyheads and resuspending them in water. This expansion step was inhibited by the presence of 100 mM phosphate. Cleavage of prehead-like polyheads to the 41-kDa gp23+ either between residues 142 and 143 by V8 protease or between residues 143 and 144 by trypsin rendered the polyheads unable to expand. In contrast, cleaved/expanded gp23* polyheads became resistant to cleavage to gp23+. As revealed by difference maps, the 7.3-kDa mass was additionally missing at the corners where the delta-piece trimers contact the protomers.

Bacteriophage T4↗