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Biomedical subjects

Martin Braun

Publications and source records attributed to Martin Braun.

At least 19 recordsLinked to original sources
PubMed2006

Axial coordination of heme in ferric CcmE chaperone characterized by EPR spectroscopy.

In Escherichia coli cytochrome c maturation requires a set of eight proteins including the heme chaperone CcmE, which binds heme transiently, yet covalently. Several variants of CcmE were purified and analyzed by continuous-wave electron paramagnetic resonance, electron nuclear double resonance, and hyperfine sublevel correlation spectroscopy to investigate the heme axial coordination. Results reveal the presence of a number of coordination environments, two high-spin heme centers with different rhombicities, and at least one low-spin heme center. The low-spin species was shown to be an artifact induced by the presence of available histidines in the vicinity of the iron. Both of the high-spin forms are five-coordinated, and comparison of the spectra of the wild-type CcmE with those of the mutant CcmE(Y134H) proves that the higher-rhombicity form is coordinated by Tyr134. The low-rhombicity (axial) form does not have a histidine residue or a water molecule as an axial ligand. However, we identified exchangeable protons coupled to the iron ion. We propose that the axial form can be coordinated by a carboxyl group of an acidic residue in the flexible domain of the protein. The two species would represent two different conformations of the flexible alpha-helix domain surrounding the heme. This conformational flexibility confers CcmE special dynamic properties that are certainly important for its function.

Bacterial Outer Membrane Proteins↗
PubMed2006

A retrospective study of the spectral probability of spontaneous otoacoustic emissions: rise of octave shifted second mode after infancy.

The recording of otoacoustic emissions (OAEs) is today a widely used tool in medical diagnosis. The mechanisms of OAE generation in the cochlea and their transmission to the external ear canal, however, are not well understood and a matter of long-standing debates. Here, the frequency distribution of 1660 spontaneous otoacoustic emissions (SOAEs) from three surveys, covering 296 human subjects, is analyzed. Neonates show a monomodal distribution with a peak at 4 kHz, but both children (5-11 y) and adults show an identical bimodal distribution, with two peaks in an octave distance (1.5 and 3 kHz). For the combined children and adult data, distribution density at the two peak tops is 2.8 and 2.7 times as high as at the low between them. Mean SOAE amplitudes are unrelated to the two peaks, but show a significant narrow-band dip precisely at the low in between at 2140 Hz (P<0.008). External ear canal resonance can explain the single 4 kHz mode at birth and the 3 kHz mode in children and adults. The octave shifted 1.5 kHz mode remains without mechanical explanation. It may reflect descending neural influence from central octave band processing. The results are relevant for the interpretation of OAE levels in medical diagnosis.

Acoustic Stimulation↗
PubMed2005

Carbamazepine induced pitch shift and octave space representation.

Octave-circular pitch perception, the repetition of pitch scale qualities when surpassing the octave interval, has been observed in behavioral data from humans and monkeys, but the underlying anatomy and physiology is still unknown. Here we analyze octave circularity in a concert pianist with absolute pitch, both under medication with the neurotropic drug carbamazepine (CBZ) and without medication. Analysis of 4619 responses in a pitch identification task revealed an internal tone-scale representation, based on the norm-tone scale re A4=440 Hz, with an octave-circular pattern of strongly and weakly represented tones. CBZ caused a global down-shift of pitch (ca. 1 semitone at 500 Hz), but no down-shift of the octave-circular pattern of tone characteristics. This pattern was similar in the six tested octave ranges (32.7-2093 Hz), both under the control and the CBZ condition. Pattern repetition always occurred at octave intervals and did not reflect the stretched octaves of piano tuning. The results indicate that CBZ influences pitch detection peripheral of an octave-circular pitch representation. Thus they support previous evidence for pitch detection in the auditory midbrain and for octave-circular pitch mapping in the auditory thalamus.

Acoustic Stimulation↗
PubMed2005

Unusual heme-histidine bond in the active site of a chaperone.

The heme chaperone CcmE is essential for the delivery of heme to c-type cytochromes. It forms an unusual transient, yet covalent, bond between an essential histidine, H130, and heme. We report on the discovery of the chemical structure of this bond solved by NMR, where the heme vinyl is cross-linked at the beta carbon to the Ndelta1 of H130. As this type of heme linkage has not been described previously in any cytochrome or hemoprotein, it represents a novel type of heme-histidine complex.

Amino Acid Sequence↗
PubMed2005

Dermatofibrosarcoma protuberans of the forehead and scalp with involvement of the outer calvarial plate: multistaged repair with the use of skin expanders.

BACKGROUND AND OBJECTIVE: Dermatofibrosarcoma protuberans (DFSP) is a locally aggressive and infiltrative tumor that requires Mohs' micrographic surgery or wide excision to treat. Adequate excision often leaves a cosmetic disfiguring defect, particularly if the tumor is located on the head and neck. Complex defects of the face present special problems, such as distortion, ectropion, and retraction of normal tissues. PATIENT AND METHODS: We present a case of an infiltrating DFSP of the forehead and scalp in a young woman. The tumor was removed, and the defect was reconstructed with multistaged repair, which included bone coverage, local and regional flaps, and the use of expanders. RESULTS: A multistaged repair was performed with good clinical outcome and satisfactory cosmetic results. CONCLUSION: Multistaged repair of the face is a viable alternative surgical approach to preserve facial contours and minimize distortion in the treatment of DFSP. This case illustrates the degree of complexity that the treatment of DFSP may involve.

Adult↗
PubMed2005

The island pedicle flap.

BACKGROUND: Surgical defects following the extirpation of cutaneous neoplasia may present challenges to the dermatologic surgeon. There are many repair options for an individual defect, including second-intention healing, primary closure, skin graft, and skin flap closure. The island pedicle flap is a random pattern advancement flap well suited to reconstruct a variety of small- to intermediate-sized soft tissue wounds. OBJECTIVE: To review the utility of the island pedicle flap in reconstructive dermatologic surgery and to detail the operative technique to achieve reproducible functional and esthetic results. METHODS: The method of flap reconstruction is presented. A variety of defects repaired with this technique are reviewed. RESULTS: The subcutaneous island pedicle flap yielded excellent functional and cosmetic repair of the presented defects with minimal operative morbidity. Secondary to a well-preserved central vascular pedicle, complications are infrequent. CONCLUSIONS: The random pattern island pedicle flap is a versatile and robust flap used to repair a variety of soft tissue wounds in a single-stage procedure with reproducible operative outcomes.

Humans↗
PubMed2005

Cytochrome c maturation and the physiological role of c-type cytochromes in Vibrio cholerae.

Vibrio cholerae lives in different habitats, varying from aquatic ecosystems to the human intestinal tract. The organism has acquired a set of electron transport pathways for aerobic and anaerobic respiration that enable adaptation to the various environmental conditions. We have inactivated the V. cholerae ccmE gene, which is required for cytochrome c biogenesis. The resulting strain is deficient of all c-type cytochromes and allows us to characterize the physiological role of these proteins. Under aerobic conditions in rich medium, V. cholerae produces at least six c-type cytochromes, none of which is required for growth. Wild-type V. cholerae produces active fumarate reductase, trimethylamine N-oxide reductase, cbb3 oxidase, and nitrate reductase, of which only the fumarate reductase does not require maturation of c-type cytochromes. The reduction of nitrate in the medium resulted in the accumulation of nitrite, which is toxic for the cells. This suggests that V. cholerae is able to scavenge nitrate from the environment only in the presence of other nitrite-reducing organisms. The phenotypes of cytochrome c-deficient V. cholerae were used in a transposon mutagenesis screening to search for additional genes required for cytochrome c maturation. Over 55,000 mutants were analyzed for nitrate reductase and cbb3 oxidase activity. No transposon insertions other than those within the ccm genes for cytochrome c maturation and the dsbD gene, which encodes a disulphide bond reductase, were found. In addition, the role of a novel CcdA-like protein in cbb3 oxidase assembly is discussed.

Base Sequence↗
PubMed2005

Cardiovascular, hormone, and lipid responses to stress induced by virtual crane handling.

OBJECTIVES: The aim of the study was to test whether a mixed-mock-up-simulator (MMU-simulator) is suitable for on-the-job training by measuring stress reactions induced by handling a crane in a virtual environment in subjects not experienced in crane operation. MATERIALS AND METHODS: A MMU-simulator in a virtual environment was developed. Twenty three individuals were randomly divided into Group 1 (n = 13) and Group 2 (n = 10). They had the task of transporting a weight over barriers with a virtual crane twice in two 15-min intervals with a 15-min break in between. Acoustical and optical disturbances were generated as an additional strain for Group 1 in the second interval and for Group 2 in the first interval. Heart rate (HR) and blood pressure (BP) were measured consecutively in both groups, blood sampling was performed in Group 1. Plasma concentrations of stress hormones and lipids were analyzed. Data were calculated as the percentage of baseline values. RESULTS: Compared to rest courses, strain led to a significant increase in HR and BP except diastolic BP in Group 2. Apart from an increased systolic BP under additional stress in Group 2, no significant differences were found between the two strain courses. Concentrations of epinephrine showed the highest increase under strain with a mean of 67%. The mean increase in norepinephrine and cortisol was 23% and 7%, respectively, whereas a 4% increase was observed for total cholesterol and high density lipoprotein cholesterol. These differences between "Rest" and "Strain" were significant. After adjusting for total plasma protein concentration, stress hormones, but not lipids, were still significantly higher during strain. CONCLUSIONS: The elevation in lipids during acute stress could be interpreted as an effect of hemoconcentration due to vasoconstriction by catecholamines. The significant increase in cardiovascular parameters and stress hormones during the tasks demonstrate that working in a virtual environment generates mental strain and that the developed MMU-simulator appears to be a promising device for on-the-job training. However, further research is necessary to validate the usefulness of virtual training by means of a comparative study of virtual and real-world training.

Adult↗
PubMed2004

A heme tag for in vivo synthesis of artificial cytochromes.

A genetic approach is described here that enables the specific covalent attachment of heme via a short C-terminal peptide tag to an otherwise non-heme-binding protein. Covalent attachment of heme to the apo-protein is catalysed by the cytochrome c maturation system of Escherichia coli. While its original enzymatic activity is retained, the resulting heme-tagged protein is red, has peroxidase activity and is redox active. The presence or absence of a C-terminal histidine tag results in low-spin heme iron with six- or high-spin heme iron with five coordinate ligands, respectively. The heme tag can be used as a tool for the rational design of artificial c-type cytochromes and metalloenzymes, thereby overcoming previous limitations set by chemical approaches. Moreover, the tag allows direct visualisation of the red fusion protein during purification.

Amino Acid Sequence↗
PubMed2004

Biosynthesis of artificial microperoxidases by exploiting the secretion and cytochrome c maturation apparatuses of Escherichia coli.

Microperoxidases were initially isolated as peptide fragments containing covalently bound heme and are derived from naturally occurring c-type cytochromes. They are not only used as model compounds but also have potential applications as biosensors, electron carriers, photoreceptors, microzymes, and drugs. In a systematic attempt to define the minimal requirements for covalent attachment of hemes to c-type cytochromes, we have succeeded to produce artificial microperoxidases with peptide sequences that do not occur naturally and can be manipulated. The in vivo production of these microperoxidases requires targeting of the peptide to the bacterial periplasm, proteolytic processing of the signal peptide, and covalent attachment of heme to the signature motif CXXCH by the cytochrome c maturation proteins CcmA-H. The peptides that bind heme carry a C-terminal histidine tag, presumably to stabilize the heme peptide. We present a heme cassette that is the basis for the de novo design of functional hemoproteins.

Bradyrhizobium↗
PubMed2004

Recording atrial monophasic action potentials using standard pacemaker leads: an alternative way to study electrophysiology properties of the human atrium in vivo?

AF leads to electrophysiological changes, but it is not known if similar alterations also appear before the onset of the first episode of AF because invasive electrophysiological studies are not justified in otherwise symptom-free patients. To address this question requires a safe method of obtaining atrial electrophysiological parameters at no extra risk or discomfort for the patient. The aim of this study was to test if recording of monophasic action potentials (MAPs) is feasible during pacemaker implantation. The study included 22 patients undergoing pacemaker implantation for symptomatic bradycardia without any history of AF. Using a custommade amplifier and a minor modification of the routine procedure for intraoperatively measured P waves, atrial electrograms could be recorded using a standard active pacemaker lead. MAP-like electrograms were obtained in 15 patients. MAP amplitude was 2.6 +/- 0.3 mV, mean action potential duration was 316 +/- 12 ms at a spontaneous heart rate of 67.2 +/- 3.2 beats/min. MAP duration was decreased when atria were stimulated at shorter cycle lengths (249 +/- 12 ms at 150 beats/min, P <0.05 vs sinus rhythm). In about two thirds of patients undergoing pacemaker implantation, recording of MAP-like electrograms was feasible with only minor modification of the atrial electrogram recording technique. The method should allow screening patients for electrophysiological alterations even before the onset of AF.

Aged↗
PubMed2003

Electrostatic complexation and photoinduced electron transfer between Zn-cytochrome c and [olyanionic fullerene dendrimers.

Two dendritic fullerene (DF) monoadducts, 2 and 3, which can carry up to 9 and 18 negative charges, respectively, were examined with respect to electrostatic complexation with Cytochrome c (Cytc). To facilitate comprehensive photophysical investigations, the zinc analogue of Cytc (ZnCytc) was prepared according to a novel, modified procedure. The association of ZnCytc and DF, and consequential photoinduced electron transfer within ZnCytc-DF from the photoexcited protein to the fullerene, was proven by fluorescence spectroscopy and transient absorption spectroscopy. These findings were also supported by circular dichroism as well as by extensive molecular dynamics (MD) simulations.

Anions↗
PubMed2003

Glycoxidation and inflammation in chronic haemodialysis patients.

BACKGROUND: Uraemia and haemodialysis treatment are associated with microinflammation and oxidative as well as carbonyl stress, which result in enhanced formation of glycoxidation products. Although both glycoxidation and inflammation can contribute to severe vascular and cardiovascular complications, the role that these pathogenic mechanisms play in the complex response of the whole organism remains to be elucidated. METHODS: We performed a cross-sectional study in 34 clinically stable chronic haemodialysis patients and in 14 healthy controls while determining serum concentrations of pentosidine, fluorescent advanced glycation end-products (AGEs), advanced oxidation protein products (AOPPs) and acute phase reactants. We further assessed the relationship between these glycoxidation products and parameters of inflammation. RESULTS: Glycoxidation products as well as certain acute phase reactants were elevated in haemodialysis patients. There were significant correlations between AOPPs and inflammatory parameters such as orosomucoid (0.39, P < 0.05), fibrinogen (0.49, P < 0.05) and pregnancy-associated protein A (PAPP-A; 0.46, P < 0.05), but no correlations between pentosidine or fluorescent AGEs and any of the inflammatory parameters. CONCLUSION: Oxidative damage showed a closer relationship to inflammation than advanced glycation (glycoxidation). AOPPs may represent a superior acute biochemical marker, whereas AGEs may better describe chronic long-lasting damage.

Acute-Phase Proteins↗
PubMed2003

Regulation of protein kinase C isozyme and calcineurin expression in isoproterenol induced cardiac hypertrophy.

Protein kinase C (PKC) and calcineurin are known to play a pivotal role in the development of cardiomyocyte growth. However, its role in Isoproterenol-induced (Iso) cardiac hypertrophy has not been characterized so far and were focus of the current study. After chronic beta-adrenergic stimulation of male Wistar rats with Iso (2mg/kg x day) for 2 and 7 days using osmotic minipumps, we determined a) cardiac PKC-activity, b) the expression of cardiac PKC isozymes (PKC-alpha, PKC-delta and PKC-epsilon) both at the protein and the mRNA-level and c) the expression of calcineurin using Western blot analysis. Iso-treatment for 2 and 7 days results in cardiac hypertrophy with an increase of the heart weight-to-body weight ratio by 36% and 27%. Iso-induced myocardial growth was associated with an enhanced total PKC-activity and a significant increased protein expression of cytosolic PKC-alpha (day 2: +38%; day 7: +43%), PKC-delta (day 2: 85%; day 7: +78%) and PKC-epsilon (day 7: +58%). The protein amount of calcineurin was not significantly altered by Iso compared with sham-operated controls. The increased expression of PKC-alpha, PKC-delta and PKC-epsilon in the cytosol was paralleled by a transcriptional upregulation of the absolute mRNA-levels of these PKC-isozymes as determined by quantitative RT-PCR.

Adrenergic beta-Agonists↗
PubMed2002

Modulation of catecholamine responsiveness and beta-adrenergic receptor/adenylyl cyclase pathway during cardiac allograft rejection1 2.

BACKGROUND: This study investigated the changes of catecholamine responsiveness and beta-adrenergic receptor/adenylyl cyclase pathway during acute cardiac transplant rejection. METHODS: Isogeneic Lewis to Lewis and allogeneic Dark Agouti (DA) to Lewis rat cardiac transplants were studied 3 and 5 days after heterotopic intraabdominal transplantation (n=6/group). Myocardial blood flow (MBF), left ventricular systolic pressure (LVSP), maximum pressure development (+dP/dt), and end-diastolic pressure (LVEDP) were measured using an intraventricular balloon. Contractile response to dobutamine (5 microg/kg/min) was also assessed. In separate groups beta-adrenergic receptor density and adenylyl cyclase activity were measured in the grafts, in the recipients' native hearts and in native hearts of sham-operated controls. RESULTS: During mild to moderate rejection cardiac function indices remained unchanged, although MBF and contractile response to dobutamine decreased significantly (P<0.05) in the allogeneic group. The beta-adrenergic receptor density was significantly (P<0.05) increased in both isografts and allografts and in the native hearts of allografted recipients in comparison to native hearts of controls. Adenylyl cyclase activity showed a significant decrease (P<0.05) only in allografts. During severe rejection, LVSP and +dP/dt decreased and LVEDP increased in allografts in comparison to isografts (P<0.05). This was accompanied by a significant decrease in MBF, contractile response to dobutamine, beta-adrenergic receptor density, and adenylyl cyclase activity (P<0.05). CONCLUSIONS: Both microcirculatory disturbances and primary alteration in adenylyl cyclase activity may contribute to decreased contractile reserve in mild to moderate cardiac allograft rejection, whereas beta-adrenergic receptor density seems to be also influenced by cardiac denervation. Severe rejection leads to systolic and diastolic heart failure with complex dysregulation of the beta-adrenergic receptor/adenylyl cyclase pathway and impaired microcirculation.

Adenylyl Cyclases↗
PubMed2002

Imp/OstA is required for cell envelope biogenesis in Escherichia coli.

In Gram-negative bacteria, all components of the outer membrane are synthesized in the cytoplasm or the cytoplasmic leaflet of the inner membrane and must thus traverse the inner membrane and the periplasm on the way to their final destination. In this study, we show Imp/OstA to have characteristics typical for proteins involved in envelope biogenesis. Imp is essential and forms a high-molecular-weight disulphide-bonded complex in the outer membrane. Upon depletion of Imp, lipids and outer membrane proteins appear in a novel membrane fraction with higher density than the outer membrane. We propose Imp to be part of a targeting/usher system for components of the outer membrane.

Amino Acid Sequence↗
PubMed2002

Characterization of an ADP-ribosyltransferase toxin (AexT) from Aeromonas salmonicida subsp. salmonicida.

An ADP-ribosylating toxin named Aeromonas salmonicida exoenzyme T (AexT) in A. salmonicida subsp. salmonicida, the etiological agent of furunculosis in fish, was characterized. Gene aexT, encoding toxin AexT, was cloned and characterized by sequence analysis. AexT shows significant sequence similarity to the ExoS and ExoT exotoxins of Pseudomonas aeruginosa and to the YopE cytotoxin of different Yersinia species. The aexT gene was detected in all of the 12 A. salmonicida subsp. salmonicida strains tested but was absent from all other Aeromonas species. Recombinant AexT produced in Escherichia coli possesses enzymatic ADP-ribosyltransferase activity. Monospecific polyclonal antibodies directed against purified recombinant AexT detected the toxin produced by A. salmonicida subsp. salmonicida and cross-reacted with ExoS and ExoT of P. aeruginosa. AexT toxin could be detected in a wild type (wt) strain of A. salmonicida subsp. salmonicida freshly isolated from a fish with furunculosis; however, its expression required contact with RTG-2 rainbow trout gonad cells. Under these conditions, the AexT protein was found to be intracellular or tightly cell associated. No AexT was found when A. salmonicida subsp. salmonicida was incubated in cell culture medium in the absence of RTG-2 cells. Upon infection with wt A. salmonicida subsp. salmonicida, the fish gonad RTG-2 cells rapidly underwent significant morphological changes. These changes were demonstrated to constitute cell rounding, which accompanied induction of production of AexT and which led to cell lysis after extended incubation. An aexT mutant which was constructed from the wt strain with an insertionally inactivated aexT gene by allelic exchange had no toxic effect on RTG-2 cells and was devoid of AexT production. Hence AexT is directly involved in the toxicity of A. salmonicida subsp. salmonicida for RTG-2 fish cells.

ADP Ribose Transferases↗