866 research outputs found
ABC transporters: Lessons from a bacterial oligopeptide uptake system
Get PDFABC transporters are proteins that are involved in the uptake of nutrients and excretion of harmful substances in biological cells. Defects in human ABC transporters can result in severe diseases. Too high ABC transporter activity can lead to non-responsiveness of cancercells to chemotherapy, and resistance of bacteria to antibiotics. Every life-form, from the most simple bacterium to the highly complex human being, contains ABC transporters. In this thesis a bacterial ABC transporter was studied to learn more about how ABC transporters work in general. The subject of investigation, the oligopeptide ABC transporter, was purified from bacteria and studied using biochemical and biopysical techniques. In this way it was elucidated what kind of substances are taken up via the oligopeptide ABC transporter and how this protein works.
Bacterial osmosensing: (B. Poolman)8 [email protected] (J.J. Spitzer)8 [email protected]
No full textBacterial osmosensing: roles of membrane structure and electrostatics in lipid-protein and protein-protein interactions Poolman, B.; Spitzer, J.J.; Wood, J.A.; Wood, Janet M. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. Abstract Bacteria act to maintain their hydration when the osmotic pressure of their environment changes. When the external osmolality decreases (osmotic downshift), mechanosensitive channels are activated to release low molecular weight osmolytes (and hence water) from the cytoplasm. Upon osmotic upshift, osmoregulatory transporters are activated to import osmolytes (and hence water). Osmoregulatory channels and transporters sense and respond to osmotic stress via different mechanisms. Mechanosensitive channel MscL senses the increasing tension in the membrane and appears to gate when the lateral pressure in the acyl chain region of the lipids drops below a threshold value. Transporters OpuA, BetP and ProP are activated when increasing external osmolality causes threshold ionic concentrations in excess of about 0.05 M to be reached in the proteoliposome lumen. The threshold activation concentrations for the OpuA transporter are strongly dependent on the fraction of anionic lipids that surround the cytoplasmic face of the protein. The higher the fraction of anionic lipids, the higher the threshold ionic concentrations. A similar trend is observed for the BetP transporter. The lipid dependence of osmotic activation of OpuA and BetP suggests that osmotic signals are transmitted to the protein via interactions between charged osmosensor domains and the ionic headgroups of the lipids in the membrane. The charged, C-terminal domains of BetP and ProP are important for osmosensing. The C-terminal domain of ProP participates in homodimeric coiled-coil formation and it may interact with the membrane lipids and soluble protein ProQ. The activation of ProP by lumenal, macromolecular solutes at constant ionic strength indicates that its structure and activity may also respond to macromolecular crowding. This excluded volume effect may restrict the range over which the osmosensing domain can electrostatically interact. A simplified version of the dissociative double layer theory is used to explain the activation of the transporters by showing how changes in ion concentration could modulate interactions between charged osmosensor domains and charged lipid or protein surfaces. Importantly, the relatively high ionic concentrations at which osmosensors become activated at different surface charge densities compare well with the predicted dependence of dcriticalT ion concentrations on surface charge density. The critical ion concentrations represent transitions in Maxwellian ionic distributions at which the surface potential reaches 25.7 mV for monovalent ions. The osmosensing mechanism is qualitatively described as an bON/OFF switchQ representing thermally relaxed and electrostatically locked protein conformations.
On the osmotic signal and osmosensing mechanism of an ABC transport system
Get PDFWat verandert er in het zenuwstelsel als een dier iets leert? Hoe worden herinneringen opgeslagen in de hersenen? Hieraan ten grondslag ligt het vermogen
van het zenuwstelsel om zich aan wisselende omstandigheden aan te passen, of, met andere woorden, plastisch te zijn. Zoals elk orgaan zijn onze hersenen opgebouwd uit afzonderlijke cellen, de hersencellen ofwel neuronen. De werking van de hersenen berust op de communicatie tussen de neuronen. De communicatie vindt
plaats op plaatsen waar de membranen van neuronen heel dicht bij elkaar liggen, de zogenaamde synapsen...
Zie: Chapter 8
Multiple-Peptidase Mutants of Lactococcus lactis Are Severely Impaired in Their Ability To Grow in Milk
Get PDFTo examine the contribution of peptidases to the growth of Lactococcus lactis in milk, 16 single- and multiple-deletion mutants were constructed. In successive rounds of chromosomal gene replacement mutagenesis, up to all five of the following peptidase genes were inactivated (fivefold mutant): pepX, pepO, pepT, pepC, and pepN. Multiple mutations led to slower growth rates in milk, the general trend being that growth rates decreased when more peptidases were inactivated. The fivefold mutant grew more than 10 times more slowly in milk than the wild-type strain. In one of the fourfold mutants and in the fivefold mutant, the intracellular pools of amino acids were lower than those of the wild type, whereas peptides had accumulated inside the cell. No significant differences in the activities of the cell envelope-associated proteinase and of the oligopeptide transport system were observed. Also, the expression of the peptidases still present in the various mutants was not detectably affected. Thus, the lower growth rates can directly be attributed to the inability of the mutants to degrade casein-derived peptides. These results supply the first direct evidence for the functioning of lactococcal peptidases in the degradation of milk proteins. Furthermore, the study provides critical information about the relative importance of the peptidases for growth in milk, the order of events in the proteolytic pathway, and the regulation of its individual components.
Haemophilus influenzae type b reemergence after combination immunization
Get PDFAn increase in Haemophilus influenzae type b (Hib) in
British children has been linked to the widespread use of a
diphtheria/tetanus/acellular pertussis combination vaccine
(DTaP-Hib). We measured anti-polyribosyl-ribitol phos-
phate antibody concentration and avidity before and after a
Hib booster in 176 children 2–4 years of age who had
received 3 doses of DTP-Hib (either DT whole cell pertus-
sis-Hib or DTaP-Hib) combination vaccine in infancy. We
also measured pharyngeal carriage of Hib. Antibody con-
centrations before and avidity indices after vaccination
were low (geometric mean concentration 0.46μg/mL, 95%
confidence interval [CI] 0.36–0.58; geometric mean avidity
index 0.16, 95% CI 0.14–0.18) and inversely related to the
number of previous doses of DTaP-Hib (p = 0.02 and
p<0.001, respectively). Hib was found in 2.1% (95% CI
0.7%–6.0%) of study participants. Our data support an
association between DTaP-Hib vaccine combinations and
clinical Hib disease through an effect on antibody concen-
tration and avidit
Point mutation in meningococcal por A gene associated with increased endemic disease
No full textThe por A gene, which encodes expression of meningococcal class 1 outer membrane protein, responsible for antigenic subtype specificity, has been cloned and sequenced in an isolate of Neisseria meningitidis (B:15:P1.7,16) from a patient in the Gloucester area with meningococcal meningitis. Comparison of the sequence with that of the equivalent gene from the P1.7,16 reference strain reveals a point mutation which generates a single aminoacid change in the epitope responsible for P1.16 specificity. Monoclonal antibodies with P1.16 specificity do not react with synthetic peptides that correspond to the altered epitope, and do not promote complement-mediated bactericidal killing of the isolate. Analysis of other strains shows widespread distribution of infections due to B:15:P1.7,16 meningococci with the altered epitope (P1.16b) in England and Wales
Modular molecular gels: Control over design, formation and properties
No full textChemE/Advanced Soft Matte
Present & Future: Visualising ideas of water infrastructure design
No full textIn redevelopment and redesign of small water structures local water governing institutions are increasingly required to and requesting that the planning processes are set up in a participatory manner. Participatory decision making processes are set up to bring stakeholders with different backgrounds, ideas, experiences and expertise together. Ideally they work collectively towards finding a solution to a problem situation. Because of their differences, stakeholders often have different ideas about the problem situation and about the ways to solve it. Discussions take place and ideas are expressed in words or text as each stakeholder tries to explain his view of the situation and possible solution. The mind, however, is more slowly stirred by the ear than by the eye. From literature about previous research activities in sociology, anthropology and systems thinking it was learnt that pictorial visuals can be used to stimulate participants to take part and strongly contribute to the analysis of the situation. Visuals could provide a better understanding of a subject than words alone could. During this research a methodology called yourScape was developed. It is made up of a number of steps that enable and stimulate stakeholders to make and use two-dimensional, still (non-moving) visuals of their ideas of small water infrastructures at present and in the future. In asking stakeholder to make their own visuals by drawing or making collages yourScape is rather unique compared to other participatory methodologies that use visuals. The research shows that own-made visuals can help stakeholders identify which differences and similarities there are in their ideas of the problem situation and of possible solutions. Through group discussions stakeholders collectively identify and analyse what these differences mean for continued work on redevelopment and redesign of small water infrastructures.Water Resources ManagementCivil Engineering and Geoscience
Toward an Improved Meningococcal Serogroup B Assay
No full textABSTRACT
Because of diverse sequences and differential expression of surface structures on individual invasive
Neisseria meningitidis
serogroup B (MenB) strains, predicting the efficacy of MenB vaccines using traditional human serum bactericidal assays (hSBA) is impractical. The meningococcal antigen surface expression (MEASURE) assay uses flow cytometry to quantitate the expression of factor H binding proteins (fHbp) contained in the bivalent rLP2086 MenB vaccine. To date, experience with MEASURE has been lacking, and in a long-awaited article, McNeil et al. (mBio 9:e00036-18,
https://doi.org/10.1128/mBio.00036-18
), provide detailed mapping of a cross-reactive antibody binding epitope and explore the potential utility of MEASURE in predicting the susceptibility of individual MenB strains to antibody-mediated killing. Remaining questions center around why some strains with high fHbp expression are nonsusceptible to anti-fHbp antibody killing. Consideration of alternative methods, such as a standardized enzyme-linked immunosorbent assay (ELISA), might offer a more readily available and reproducible assay for wider use.
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