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Search Results: 1 - 10 of 32316 matches for " Peter Hegemann "
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Ultrafast Laser Energy Density and Retinal Absorption Cross-Section Determination by Saturable Absorption Measurements  [PDF]
Alfons Penzkofer, Meike Luck, Tilo Mathes, Peter Hegemann
Journal of Analytical Sciences, Methods and Instrumentation (JASMI) , 2014, DOI: 10.4236/jasmi.2014.41003

Laser pulse nonlinear transmission measurements through saturable absorbers of known absorption parameters allow the measurement of their energy density. On the other hand, nonlinear transmission measurements of laser pulses of known energy density through absorbing media allow their absorption parameter determination. The peak energy density w0P of second harmonic pulses of a mode-locked titanium sapphire laser at wavelength λP = 400 nm is determined by nonlinear energy transmission measurement TE through the dye ADS084BE (1,4-bis(9-ethyl-3-car-bazovinylene)-2-methoxy-5-(2’-ethyl-hexyloxy)-benzene) in tetrahydrofuran. TE(w0P) calibration curves are calculated for

Bimodal Activation of Different Neuron Classes with the Spectrally Red-Shifted Channelrhodopsin Chimera C1V1 in Caenorhabditis elegans
Karen Erbguth, Matthias Prigge, Franziska Schneider, Peter Hegemann, Alexander Gottschalk
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0046827
Abstract: The C. elegans nervous system is particularly well suited for optogenetic analyses of circuit function: Essentially all connections have been mapped, and light can be directed at the neuron of interest in the freely moving, transparent animals, while behavior is observed. Thus, different nodes of a neuronal network can be probed for their role in controlling a particular behavior, using different optogenetic tools for photo-activation or –inhibition, which respond to different colors of light. As neurons may act in concert or in opposing ways to affect a behavior, one would further like to excite these neurons concomitantly, yet independent of each other. In addition to the blue-light activated Channelrhodopsin-2 (ChR2), spectrally red-shifted ChR variants have been explored recently. Here, we establish the green-light activated ChR chimera C1V1 (from Chlamydomonas and Volvox ChR1′s) for use in C. elegans. We surveyed a number of red-shifted ChRs, and found that C1V1-ET/ET (E122T; E162T) works most reliable in C. elegans, with 540–580 nm excitation, which leaves ChR2 silent. However, as C1V1-ET/ET is very light sensitive, it still becomes activated when ChR2 is stimulated, even at 400 nm. Thus, we generated a highly efficient blue ChR2, the H134R; T159C double mutant (ChR2-HR/TC). Both proteins can be used in the same animal, in different neurons, to independently control each cell type with light, enabling a further level of complexity in circuit analyses.
A Set of Engineered Escherichia coli Expression Strains for Selective Isotope and Reactivity Labeling of Amino Acid Side Chains and Flavin Cofactors
Jennifer Mehlhorn, Helena Steinocher, Sebastian Beck, John T. M. Kennis, Peter Hegemann, Tilo Mathes
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0079006
Abstract: Biological reactions are facilitated by delicate molecular interactions between proteins, cofactors and substrates. To study and understand their dynamic interactions researchers have to take great care not to influence or distort the object of study. As a non-invasive alternative to a site-directed mutagenesis approach, selective isotope labeling in combination with vibrational spectroscopy may be employed to directly identify structural transitions in wild type proteins. Here we present a set of customized Escherichia coli expression strains, suitable for replacing both the flavin cofactor and/or selective amino acids with isotope enriched or chemically modified substrates. For flavin labeling we report optimized auxotrophic strains with significantly enhanced flavin uptake properties. Labeled protein biosynthesis using these strains was achieved in optimized cultivation procedures using high cell density fermentation. Finally, we demonstrate how this approach is used for a clear assignment of vibrational spectroscopic difference signals of apoprotein and cofactor of a flavin containing photoreceptor of the BLUF (Blue Light receptors Using FAD) family.
HinT proteins and their putative interaction partners in Mollicutes and Chlamydiaceae
Miriam Hopfe, Johannes H Hegemann, Birgit Henrich
BMC Microbiology , 2005, DOI: 10.1186/1471-2180-5-27
Abstract: An cluster of hitABL genes, similar to that of M. hominis was found in M. pulmonis, M. mycoides subspecies mycoides SC, M. mobile and Mesoplasma florum. RT-PCR analyses provided evidence that the P80, P60 and HinT homologues of M. pulmonis were polycistronically organized, suggesting a genetic and physical interaction between the proteins encoded by these genes in these species. While the hit loci of M. pneumoniae and M. genitalium encoded, in addition to HinT, a protein with several transmembrane segments, the hit locus of Ureaplasma parvum encoded a pore-forming protein, UU270, a P60 homologue, UU271, HinT, UU272, and a membrane protein of unknown function, UU273. Although a full-length mRNA spanning the four genes was not detected, amplification of all intergenic regions from the center of UU270 to the end of UU273 by RT-PCR may be indicative of a common, but unstable mRNA.In Chlamydiaceae the hit gene is flanked upstream by a gene predicted to encode a metal dependent hydrolase and downstream by a gene putatively encoding a protein with ARM-repeats, which are known to be involved in protein-protein interactions. In RT-PCR analyses of C. pneumoniae, regions comprising only two genes, Cp265/Cp266 and Cp266/Cp267 were able to be amplified. In contrast to this in vivo interaction analysis using the yeast two-hybrid system and in vitro immune co-precipitation revealed an interaction between Cp267, which contains the ARM repeats, Cp265, the predicted hydrolase, and Cp266, the HinT protein.In the Mollicutes HinT proteins were shown to be linked with membrane proteins while in the Chlamydiaceae they were genetically and physically associated with cytoplasmic proteins, one of which is predicted to be a metal-dependent phosphoesterase. Future work will elucidate whether these differing associations indicate that HinT proteins have evolved independently or are indeed two hotspots of a common sphere of action of bacterial HinT proteins.The detection of an unusual, highly co
Genetically encoded calcium indicators for multi-color neural activity imaging and combination with optogenetics
Jasper Akerboom,Nicole Carreras Calderón,Lin Tian,Matthias Prigge,Johan Tol?,Ronak Patel,Stefan R. Pulver,Trevor J. Wardill,Karen S. Sarkisyan,Cornelia I. Bargmann,Sebastian Kügler,Leon Lagnado,Peter Hegemann,Alexander Gottschalk,Loren L. Looger
Frontiers in Molecular Neuroscience , 2013, DOI: 10.3389/fnmol.2013.00002
Abstract: Genetically encoded calcium indicators (GECIs) are powerful tools for systems neuroscience. Here we describe red, single-wavelength GECIs, “RCaMPs,” engineered from circular permutation of the thermostable red fluorescent protein mRuby. High-resolution crystal structures of mRuby, the red sensor RCaMP, and the recently published red GECI R-GECO1 give insight into the chromophore environments of the Ca2+-bound state of the sensors and the engineered protein domain interfaces of the different indicators. We characterized the biophysical properties and performance of RCaMP sensors in vitro and in vivo in Caenorhabditis elegans, Drosophila larvae, and larval zebrafish. Further, we demonstrate 2-color calcium imaging both within the same cell (registering mitochondrial and somatic [Ca2+]) and between two populations of cells: neurons and astrocytes. Finally, we perform integrated optogenetics experiments, wherein neural activation via channelrhodopsin-2 (ChR2) or a red-shifted variant, and activity imaging via RCaMP or GCaMP, are conducted simultaneously, with the ChR2/RCaMP pair providing independently addressable spectral channels. Using this paradigm, we measure calcium responses of naturalistic and ChR2-evoked muscle contractions in vivo in crawling C. elegans. We systematically compare the RCaMP sensors to R-GECO1, in terms of action potential-evoked fluorescence increases in neurons, photobleaching, and photoswitching. R-GECO1 displays higher Ca2+ affinity and larger dynamic range than RCaMP, but exhibits significant photoactivation with blue and green light, suggesting that integrated channelrhodopsin-based optogenetics using R-GECO1 may be subject to artifact. Finally, we create and test blue, cyan, and yellow variants engineered from GCaMP by rational design. This engineered set of chromatic variants facilitates new experiments in functional imaging and optogenetics.
Characteristics of chlorophenol degradation and the 16S rRNA gene sequencing of the strain

WANG Jianlong,ZHAO Xuan,Werner Hegemann,
,赵璇,Wener Hegemann

环境科学学报 , 2003,
Abstract: 从受氯代有机物污染的土壤中富集分离到对2、4-二氯酚具有高效降解能力的微生物混合菌群。实验表明,降解1mol二氯酚可以定量释放出2mol的氯离子,在生物流化床反应器中,以聚胺酯泡沫块为固定化载体吸附固定化微生物,进行了连续降解氯酚的实验研究,当水力停留时间为24h,二氯酚的初始浓度为30μmol/L时,二氯酚的去除率均在90%以上,利用平板划线法从混合微生物菌群中分离到可以利用二氯酚为唯一碳源和能源的纯种微生物,16SrRNA基因序列分析结果表明,该微生物为Rhodococcus属。
An "Estimate & Score Algorithm" for simultaneous parameter estimation and reconstruction of incomplete data on social networks
Rachel A Hegemann, Erik A Lewis and Andrea L Bertozzi
Security Informatics , 2013, DOI: 10.1186/2190-8532-2-1
Abstract: Dynamic activity involving social networks often has distinctive temporal patterns that can be exploited in situations involving incomplete information. Gang rivalry networks, in particular, display a high degree of temporal clustering of activity associated with retaliatory behavior. A recent study of a Los Angeles gang network shows that known gang activity between rivals can be modeled as a self-exciting point process on an edge of the rivalry network. In real-life situations, data is incomplete and law-enforcement agencies may not know which gang is involved. However, even when gang activity is highly stochastic, localized excitations in parts of the known dataset can help identify gangs responsible for unsolved crimes. Previous work successfully incorporated the observed clustering in time of the data to identify gangs responsible for unsolved crimes. However, the authors assumed that the parameters of the model are known, when in reality they have to be estimated from the data itself. We propose an iterative method that simultaneously estimates the parameters in the underlying point process and assigns weights to the unknown events with a directly calculable score function. The results of the estimation, weights, error propagation, convergence and runtime are presented.
The Chlamydia pneumoniae Invasin Protein Pmp21 Recruits the EGF Receptor for Host Cell Entry
Katja M?lleken,Elisabeth Becker,Johannes H. Hegemann
PLOS Pathogens , 2013, DOI: 10.1371/journal.ppat.1003325
Abstract: Infection of mammalian cells by the strictly intracellular pathogens Chlamydiae requires adhesion and internalization of the infectious Elementary Bodies (EBs). The components of the latter step were unknown. Here, we identify Chlamydia pneumoniae Pmp21 as an invasin and EGFR as its receptor. Modulation of EGFR surface expression evokes correlated changes in EB adhesion, internalization and infectivity. Ectopic expression of EGFR in EGFR-negative hamster cells leads to binding of Pmp21 beads and EBs, thus boosting the infection. EB/Pmp21 binding and invasion of epithelial cells results in activation of EGFR, recruitment of adaptors Grb2 and c-Cbl and activation of ERK1/2, while inhibition of EGFR or MEK kinase activity abrogates EB entry, but not attachment. Binding of Grb2 and c-Cbl by EGFR is essential for infection. This is the first report of an invasin-receptor interaction involved in host-cell invasion by any chlamydial species.
Partial Recovery of Audiological, Vestibular, and Radiological Findings following Spontaneous Intralabyrinthine Haemorrhage
Thomas Pézier,Krisztina Baráth,Stefan Hegemann
Case Reports in Otolaryngology , 2013, DOI: 10.1155/2013/941530
Abstract: The diagnosis, work-up, and treatment of sudden sensorineural hearing loss and sudden vestibular loss vary widely between units. With the increasing access to both magnetic resonance imaging and objective vestibular testing, our understanding of the various aetiologies at hand is increasing. Despite this, the therapeutic options are limited and without a particularly strong evidence base. We present a rare, yet increasingly diagnosed, case of intralabyrinthine haemorrhage (ILH) together with radiological, audiological, and vestibular test results. Of note, this occurred spontaneously and has shown partial recovery in all the mentioned modalities. 1. Introduction Sudden sensorineural hearing loss (SSNHL) was first described by de Kleyn in 1944 [1]. Today, it is defined as a sensori-neural hearing loss of >30?dB across at least 3 consecutive frequencies arising in <72 hours [2, 3]. It is generally unilateral and reports of its annual incidence vary from 5 to 300/100,000 [4, 5]. Up to 90% of cases are idiopathic [6] and treatment is generally with steroids, though the evidence supporting this is controversial [7–9] especially as spontaneous improvement occurs in >50% of patients within 2 weeks [6, 10, 11]. The specific type of steroid, its dose/duration, and method of delivery vary widely from unit to unit. Our unit uses very high dose oral dexamethasone and we have recently published encouraging results [12]. Intralabyrinthine haemorrhage (ILH) as a cause of SSNHL is extremely rare, and there have been few such reports in the literature [13–18]. The relationship of vestibular symptoms with spontaneous ILH is also unclear. Generally, haemorrhage occurs in patients with coagulopathies as seen in leukaemia or with anticoagulant medication and very few patients enjoy any recovery of function. 2. Case Report A 50-year-old journalist presented to the ENT department at the University Hospital Zurich, with left-sided tinnitus, hearing loss, and general dizziness without real vertigo. The symptoms had suddenly appeared whilst at work a month previously and he had been treated by a private ENT doctor with oral prednisolone (50?mg daily for 10 days), betahistine, magnesium, and flunarizine with a diagnosis of an acute idiopathic vestibulocochlear loss. During this time his hearing loss had remained, but his dizziness symptoms had almost completely resolved. He also complained of tinnitus and a pressure sensation on the left ear. There was no further medical history of note other than that he took 100?mg aspirin daily because of borderline increased hematocrit. He
Wild Skylarks Seasonally Modulate Energy Budgets but Maintain Energetically Costly Inflammatory Immune Responses throughout the Annual Cycle
Arne Hegemann, Kevin D. Matson, Maaike A. Versteegh, B. Irene Tieleman
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0036358
Abstract: A central hypothesis of ecological immunology is that immune defences are traded off against competing physiological and behavioural processes. During energetically demanding periods, birds are predicted to switch from expensive inflammatory responses to less costly immune responses. Acute phase responses (APRs) are a particularly costly form of immune defence, and, hence, seasonal modulations in APRs are expected. Yet, hypotheses about APR modulation remain untested in free-living organisms throughout a complete annual cycle. We studied seasonal modulations in the APRs and in the energy budgets of skylarks Alauda arvensis, a partial migrant bird from temperate zones that experiences substantial ecological changes during its annual cycle. We characterized throughout the annual cycle changes in their energy budgets by measuring basal metabolic rate (BMR) and body mass. We quantified APRs by measuring the effects of a lipopolysaccharide injection on metabolic rate, body mass, body temperature, and concentrations of glucose and ketone. Body mass and BMR were lowest during breeding, highest during winter and intermediate during spring migration, moult and autumn migration. Despite this variation in energy budgets, the magnitude of the APR, as measured by all variables, was similar in all annual cycle stages. Thus, while we find evidence that some annual cycle stages are relatively more energetically constrained, we find no support for the hypothesis that during these annual cycle stages birds compromise an immune defence that is itself energetically costly. We suggest that the ability to mount an APR may be so essential to survival in every annual cycle stage that skylarks do not trade off this costly form of defence with other annual cycle demands.
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