Biomedical subjects

V Braun

Publications and source records attributed to V Braun.

At least 109 records · Page 6Linked to original sources

PubMed1995

Signal transfer through three compartments: transcription initiation of the Escherichia coli ferric citrate transport system from the cell surface.

Transport of ferric citrate into cells of Escherichia coli K-12 involves two energy-coupled transport systems, one across the outer membrane and one across the cytoplasmic membrane. Previously, we have shown that ferric citrate does not have to enter the cytoplasm of E. coli K-12 to induce transcription of the fec ferric citrate transport genes. Here we demonstrate that ferric citrate uptake into the periplasmic space between the outer and the cytoplasmic membranes is not required for fec gene induction. Rather, FecA and the TonB, ExbB and ExbD proteins are involved in induction of the fec transport genes independent of their role in ferric citrate transport across the outer membrane. The uptake of ferric citrate into the periplasmic space of fecA and tonB mutants via diffusion through the porin channels did not induce transcription of fec transport genes. Point mutants in FecA displayed the constitutive expression of fec transport genes in the absence of ferric citrate but still required TonB, with the exception of one FecA mutant which showed a TonB-independent induction. The phenotype of the FecA mutants suggests a signal transduction mechanism across three compartments: the outer membrane, the periplasmic space and the cytoplasmic membrane. The signal is triggered upon the interaction of ferric citrate with FecA protein. It is postulated that FecA, TonB, ExbB and ExbD transfer the signal across the outer membrane, while the regulatory protein FecR transmits the signal across the cytoplasmic membrane to FecI in the cytoplasm. FecI serves as a sigma factor which facilitates binding of the RNA polymerase to the fec transport gene promoter upstream of fecA.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1995

Selective peripheral denervation for spasmodic torticollis: is the outcome predictable?

If botulinum toxin fails in the treatment of cervical dystonia, selective peripheral denervation is now accepted as the best surgical option. Despite the very promising results, however, there is still a substantial group of patients who do not benefit from this procedure. Positive response to prior botulinum toxin therapy seems to be a very good predictor of outcome after selective peripheral denervation (P < 0.01). The meaning of the histological findings of the resected nerves is uncertain. Patients with histologically proven pathological nerves do not seem to benefit more than patients with histological normal ones (P < 0.30).

Botulinum Toxins↗

PubMed1995

A clonal translocation t(10;21) in an optic glioma of a patient with neurofibromatosis type 1 (NF 1).

An 11-year-old boy affected by neurofibromatosis type 1 is presented with severely impaired vision on the right eye (0.1). MRI demonstrated a 2.3 x 1.8 cm tumour of the optic chiasma. After open biopsy cytogenetic analysis was performed on primary cultures of this optic glioma (grade I). A clonal translocation t(10;21)(q21.2;21.1) was detected in 66% of the metaphases analysed. The boy received fractioned irradiation with a total tumour dose of 60 Gy. The ultimate MRI taken 18 months after radiotherapy showed no residual tumour. The vision on the right improved to 0.2, but decreased on the left to 0.6. The patient attends high school with no impairment in his daily life.

Adolescent↗

PubMed1995

Shaving the hair--is it always necessary for cranial neurosurgical procedures?

Shaving of the hair and neurosurgical procedures are almost inseparably connected issues. This may add an additional psychological stress to the patient. Those departments which abandoned pre-operative shaving did not see higher infection rates. From January 1993 to September 1994 we performed 57 cranial procedures without any shaving, among them 5 shunt procedures. We found no disturbances of wound healing or septic complications. Therefore neurosurgical procedures without shaving are recommended for all benign cranial processes if a rapid rehabilitation of the patient to his normal daily life is to be expected.

Brain Diseases↗

PubMed1995

Transcriptional regulation of ferric citrate transport in Escherichia coli K-12. Fecl belongs to a new subfamily of sigma 70-type factors that respond to extracytoplasmic stimuli.

Transcription of the ferric citrate transport system of Escherichia coli K-12 is repressed by Fe(2+)-Fur and activated by ferric citrate. Ferric citrate does not have to enter the cytoplasm; it initiates a signal transduction mechanism by binding to the outer membrane receptor FecA. Presumably, a conformational change is transmitted in a TonB-dependent manner to the FecR protein. FecR activates FecI, and FecI activates transcription of the fecABCDE transport genes. In this communication, FecI was isolated after cloning fecI downstream of an ideal ribosome-binding site. Overexpressed FecI formed inclusion bodies which were solubilized and purified in active form using a mild detergent. FecI, in conjunction with RNA polymerase core enzyme, directed transcription from the fecA promoter in an in vitro run-off transcription assay. Furthermore, FecI retarded the electrophoretic mobility of a specific 75 bp DNA fragment located upstream of fecA. An in vivo competition experiment between the fecA promoters of wild-type and mutant strains identified the nucleotide positions 2747, 2749, 2751 and 2753, located within the 75 bp fragment, as important for FecI-induced transcription. Mobility band shift of fecA promoter DNA caused by cell lysates required growth of cells in the presence of ferric citrate and expression of FecA, FecI and FecR. These data support the previous assignment of FecI, based on sequence homologies, to a new subfamily of eubacterial RNA polymerase sigma 70 factors that respond to extra-cytoplasmic stimuli and regulate extracytoplasmic functions.

Bacterial Proteins↗

PubMed1995

Regulation of citrate-dependent iron transport of Escherichia coli: fecR is required for transcription activation by FecI.

Citrate-dependent Fe3+ transport into Escherichia coli K-12 is induced by iron and citrate. The inducer is probably ferric dicitrate which does not have to be taken up into the cytoplasm to induce transcription of the fec transport genes. Two regulatory genes, fecI and fecR, located upstream of the fecABCDE transport genes, are required for induction. We report that in vivo the chromosomally encoded FecI protein activates transcription of the fecA and fecB transport genes in response to ferric citrate and the FecR protein. Cells expressing chromosomally and plasmid-encoded truncated FecR derivatives no longer responded to ferric citrate and expressed the fec transport genes constitutively. The smallest active FecR derivative contained 59 amino acid residues as compared to the 317 residues of wild-type FecR. Constitutive induction was lower than induction of the FecR wild-type strain by ferric citrate. It is concluded that the N-terminal portion of FecR activates FecI and that the C-terminal portion of FecR responds to ferric citrate. Transcription of the fec transport genes is positively regulated by FecI and FecR and negatively regulated by the Fe2(+)-Fur repressor. Transcription activation and repression may occur independently of each other.

Amino Acid Sequence↗

PubMed1995

Novel colicin 10: assignment of four domains to TonB- and TolC-dependent uptake via the Tsx receptor and to pore formation.

Uptake of a new colicin, colicin 10 (Col10), into cells of Escherichia coli required TonB, ExbBD (Ton system), but its cognate receptor, Tsx, functioned independently of Ton and TolQRAB (Tol system). Uptake of Col10 also required TolC which is unique for a Ton-coupled translocation through the outer membrane. A 2470 bp DNA fragment from the natural plasmid pCol10 encoding the Col10 activity (cta), immunity (cti) and lysis (ctl) genes was sequenced. The Cta, Cti and Ctl proteins, as deduced from the nucleotide sequences, consisted of 490 (M(r) 53,342), 96 (M(r) 11,586) and 43 (M(r) 4484) amino acid residues, respectively. Col10 (Cta) was highly homologous to colicin E1 in two regions which determined the common TolC requirement for uptake and the pore-forming activity. Col10 and E1 differed entirely in the regions which are predicted to determine the Ton dependence of Col10 and the Tol dependence of E1, and binding to the receptors Tsx and BtuB, respectively. The region responsible for the Ton-dependent uptake of Col10 was localized in the sequence ranging from residues 1 to 43 (Ton region), and the region responsible for the Tol-dependent uptake of colicin E1 extended from residues 1 to 34 (Tol region). Each Tol-dependent colicin contained a pentapeptide homologous to the sequence DGSGS in the Tol region of E1 which is proposed to be implicated in Tol-dependent uptake (TolA box). After the exchange of the Ton and the Tol regions between Col10 and E1, the Col10-E1 fusion protein was carried into cells via the Ton system and BtuB, whereas the E1-Col10 fusion protein was imported via the Tol system and Tsx. Although the immunity proteins of Col10 and E1 displayed a low homology, Cti conferred full immunity to E1, in contrast to the immunity protein of E1 which did not protect cells against Col10. It is proposed that Col10 belongs to the colicin E1, Ia, Ib group as opposed to the colicin A, B, N group of pore-forming colicins. Col10 consists of 4 domains of which two are very similar and two are very different to E1, supporting our previous proposal that colicins evolved by recombination of DNA fragments which encode uptake and activity domains.

Amino Acid Sequence↗

PubMed1995

Energy-coupled transport and signal transduction through the gram-negative outer membrane via TonB-ExbB-ExbD-dependent receptor proteins.

Iron in the form of ferric siderophore complexes and vitamin B12 are transported through the outer membrane of Gram-negative bacteria by a mechanism which consumes energy. There is no known energy source in the outer membrane or in the adjacent periplasmic space so that energy is provided by the electrochemical potential across the cytoplasmic membrane. Energy flows from the cytoplasmic into the outer membrane via a complex consisting of the TonB, ExbB and ExbD proteins which are anchored in the cytoplasmic membrane. It is proposed that the TonB--ExbB--ExbD complex opens--via an energized conformation of the TonB protein--channels in the outer membrane, formed by proteins which serves as highly specific binding sites for the various ferric siderophores and vitamin B12. In addition, outer membrane receptors together with the TonB--ExbB--ExbD complex are directly involved in induction of the transcription of ferric citrate and pseudobactin transport genes of Escherichia coli and Pseudomonas putida, respectively.

Amino Acid Sequence↗

PubMed1995

Transcriptional regulation from the cell surface: conformational changes in the transmembrane protein FecR lead to altered transcription of the ferric citrate transport genes in Escherichia coli.

Ferric citrate induces the ferric citrate transport system in Escherichia coli without being taken up into cells. The cytoplasmic transmembrane protein FecR, required for the response to ferric citrate, was found to be cleaved by a cellular protease. FecR protein produced by fecR mutants impaired or constitutive in fecA transcription was protease resistant, indicating that conformational changes affect proper functioning of FecR.

Bacterial Outer Membrane Proteins↗

PubMed1995

Evidence that the immunity protein inactivates colicin 5 immediately prior to the formation of the transmembrane channel.

Determination and analysis of the nucleotide sequences of the activity, immunity, and lysis genes of colicin 5 assigned colicin 5 to the subclass of pore-forming colicins to which colicins 10, E1, Ia, Ib, and K belong. Mutational analysis of colicin 5 and exchange of DNA fragments between the most closely related colicins, colicins 5 and 10, and between their immunity proteins localized the regions that determine the reaction specificity between colicin 5 and its immunity protein to residues 405 to 424 of colicin 5, the region corresponding to the amphiphilic alpha-helix 6 of the similar colicins E1 and Ia. The specificity-conferring residues 55 to 58 and 68 to 75 of the immunity protein were localized in the cytoplasmic loop and the inner leaflet of the cytoplasmic membrane. The localization of the reactive regions of the immunity protein and the colicin close to the inner side of the cytoplasmic membrane suggests that the immunity protein inactivates colicin 5 shortly before the lethal colicin pores in the cytoplasmic membrane are opened.

Amino Acid Sequence↗

PubMed1995

Strong function-related homology between the pore-forming colicins K and 5.

Sequence determination of the Escherichia coli colicin K determinant revealed identity with the E. coli colicin 5 determinant in the immunity and lysis proteins, strong homologies in the pore-forming region (93.7%) and the Tsx receptor-binding region (77%) of the colicins, and low levels of homology (20.3%) in the N-terminal region of the colicins. This latter region is responsible for the Tol-dependent uptake of colicin K and the Ton-dependent uptake of colicin 5 in the respective colicins. During evolution, the DNA encoding colicin activity and binding to the Tsx receptor was apparently recombined with two different DNA fragments that determined different uptake routes, leading to the differences observed in colicin K and colicin 5 import.

Amino Acid Sequence↗

PubMed1995

Ferrichrome transport in Escherichia coli K-12: altered substrate specificity of mutated periplasmic FhuD and interaction of FhuD with the integral membrane protein FhuB.

FhuD is the periplasmic binding protein of the ferric hydroxamate transport system of Escherichia coli. FhuD was isolated and purified as a His-tag-labeled derivative on a Ni-chelate resin. The dissociation constants for ferric hydroxamates were estimated from the concentration-dependent decrease in the intrinsic fluorescence intensity of His-tag-FhuD and were found to be 0.4 microM for ferric aerobactin, 1.0 microM for ferrichrome, 0.3 microM for ferric coprogen, and 5.4 microM for the antibiotic albomycin. Ferrichrome A, ferrioxamine B, and ferrioxamine E, which are poorly taken up via the Fhu system, displayed dissociation constants of 79, 36, and 42 microM, respectively. These are the first estimated dissociation constants reported for a binding protein of a microbial iron transport system. Mutants impaired in the interaction of ferric hydroxamates with FhuD were isolated. One mutated FhuD, with a W-to-L mutation at position 68 [FhuD(W68L)], differed from wild-type FhuD in transport activity in that ferric coprogen supported promotion of growth of the mutant on iron-limited medium, while ferrichrome was nearly inactive. The dissociation constants of ferric hydroxamates were higher for FhuD(W68L) than for wild-type FhuD and lower for ferric coprogen (2.2 microM) than for ferrichrome (156 microM). Another mutated FhuD, FhuD(A150S, P175L), showed a weak response to ferrichrome and albomycin and exhibited dissociation constants two- to threefold higher than that of wild-type FhuD. Interaction of FhuD with the cytoplasmic membrane transport protein FhuB was studied by determining protection of FhuB degradation by trypsin and proteinase K and by cross-linking experiments. His-tag-FhuD and His-tag-FhuD loaded with aerobactin specifically prevented degradation of FhuB and were cross-linked to FhuB. FhuD loaded with substrate and also FhuD free of substrate were able to interact with FhuB.

Base Sequence↗

PubMed1995

Superlytic hemolysin mutants of Serratia marcescens.

Hemolysis by Serratia marcescens is caused by two proteins, ShlA and ShlB. ShlA is the hemolysin proper, and ShlB transports ShlA through the outer membrane, whereby ShlA is converted into a hemolysin. Superhemolytic ShlA derivatives that displayed 7- to 20-fold higher activities than wild-type ShlA were isolated. ShlA80 carried the single amino acid replacement of G to D at position 326 (G326D), ShlA87 carried S386N, and ShlA80III carried G326D and N236D. Superhemolysis was attributed to the greater stability of the mutant ShlA derivatives because they aggregated less than the wild-type hemolysin, which lost activity within 3 min at 20 degrees C. In contrast to the highly hemolytic wild-type ShlA at 0 degrees C, the hyperlytic hemolysins were nonhemolytic at 0 degrees C, suggesting that the hyperlytic derivatives differed from wild-type ShlA in adsorption to and insertion into the erythrocyte membrane. However, the size of the pores formed at 20 degrees C by superhemolytic hemolysins could not be distinguished from that of wild-type ShlA. In addition to the N-terminal sequence up to residue 238, previously identified to be important for activation and secretion, sites 326 and 386 contribute to hemolysin activity since they are contained in regions that participate in hemolysin inactivation through aggregation.

Bacterial Proteins↗

PubMed1995

Identification of receptor binding sites by competitive peptide mapping: phages T1, T5, and phi 80 and colicin M bind to the gating loop of FhuA.

Previously we proposed a transmembrane model of the FhuA receptor protein in the outer membrane of Escherichia coli. Removal of the largest loop at the cell surface converted the FhuA transport protein into an open channel and rendered cells resistant to the FhuA-specific phages T1, T5, and phi 80 and to colicin M. In the present study we employed acetylated hexapeptide amides covering the entire surface loop to investigate binding of the phages and of colicin M. Competitive peptide mapping proved to be a powerful technique to uncover three ligand binding sites within a region of 34 amino acid residues. Hexapeptides derived from three specific regions of the surface loop inhibited infection of cells by the phages and killing by colicin M. Two of these regions were common among all four FhuA ligands. Electron microscopy of phage T5 revealed that one inhibitory peptide triggered a strong conformational change leading to the release of DNA from the phage head. These results suggest that the FhuA gating loop is the target for specific binding of phages T1, T5, and phi 80 and colicin M.

Amino Acid Sequence↗

PubMed1995

[Meralgia paraesthetica and its surgical treatment].

Compression neuropathy of the lateral femoral cutaneous nerve (meralgia paresthetica) leads to pain and dysesthesia in the anterolateral thigh. Over a period of 23 1/2 years, 29 patients (33 procedures) were operated on after failure of conservative treatment: 18 patients (20 procedures) underwent neurolysis of the nerve, and in 11 the nerve was transected. The 33 procedures were necessary because 1 patient had bilateral meralgia paresthetica and there were 3 recurrences with persisting pain. The average follow-up was 32 months after neurolysis and 87 months after transection. Complete or partial pain relief was found in 72% after decompression and in 82% after transection of the nerve.

Adult↗

PubMed1995

[Spontaneous brain abscess--bacteriology, therapy and prognosis].

Spontaneous intracranial abscesses are quite rare in western industrial countries. According to the recently published papers, each neurosurgical centre is expecting 2 to 4 cases a year. Whereas in the last three years we only operated on one or two cases a year we treated 8 cases in the first ten months of 1994. Although this remarkable increase is not statistically significant, further observations seem to be indicated. In 5 cases the origin of the abscess remained unknown. 3 patients had odontogeneous focuses, 2 middle ear and 2 pulmonary infections. One patient was operated on for spontaneous liver abscess few days before. Streptococcus was found in 9 cases, Bacteroides, Nocardia and Rhodoturola in 1 case each. For one patient no pathogen could be detected. In regard of our results, minimal invasive neurosurgical aspiration of the abscess with adjacent longterm antibiotic therapy gives a good prognosis with little morbidity. In contrast the mortality rate rises if diagnostic procedures are delayed or if the detected microorganism is highly resistant to current antibiotics.

Adolescent↗

PubMed1994

Interaction of Serratia marcescens hemolysin (ShlA) with artificial and erythrocyte membranes. Demonstration of the formation of aqueous multistate channels.

Pore formation by hemolysin (ShlA) of Serratia marcescens was studied in erythrocytes and in artificial lipid bilayer membranes. The results with erythrocytes demonstrated that hemolysin pores varied in size. In erythrocyte membranes with reduced fluidity (0 degrees C), the toxin formed small pores with diameter 1-1.5 nm. In fluid membranes (above 20 degrees C), hemolysin pores with larger diameters (approximately 2.5-3.0 nm) were observed, which may be caused by association of ShlA monomers into oligomers. Comparison of the channels formed by Staphylococcus aureus alpha-toxin with channels formed by ShlA indicated a slightly smaller pore diameter of ShlA pores. Analysis of ShlA in artificial lipid bilayers showed the formation of pores with a broad distribution of single channel conductances, suggesting variable sizes of the ShlA pore. The lower limit for the pore diameter was approximately 1.0 nm. The ShlA pores did not exhibit pronounced ion selectivity nor voltage dependence, supporting the presence of a large water-filled pore.

Bacterial Toxins↗

PubMed1994

Energy-coupled transport through the outer membrane of Escherichia coli small deletions in the gating loop convert the FhuA transport protein into a diffusion channel.

Active transport of Fe3+ as ferrichrome complex through the outer membrane of Escherichia coli is mediated by the FhuA outer membrane protein and the TonB-ExbB-ExbD protein complex in the cytoplasmic membrane. The required energy is provided by the electrochemical potential of the cytoplasmic membrane which is assumed to induce a conformation of the TonB protein that causes a conformational change in FhuA so that bound ferrichrome is released into the periplasmic space located between the outer and the cytoplasmic membrane. Excision of segments as small as 12 amino acids in the largest surface loop of FhuA converted FhuA into an open channel through which ferrichrome and antibiotics diffused independent of TonB-ExbB-ExbD. It is proposed that FhuA forms a closed channel which is opened by movement of the gating loop through a kind of allosteric interaction with TonB. The gating loop is also involved in binding of all FhuA ligands which in addition to ferrichrome are the phages T1, T5, phi 80, colicin M and the antibiotic albomycin.

Amino Acid Sequence↗