| 1. |
- van Sorge, Nina M., et al.
(author)
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Bacterial protein domains with a novel Ig-like fold target human CEACAM receptors
- 2021
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In: EMBO Journal. - : Wiley-VCH Verlagsgesellschaft. - 0261-4189 .- 1460-2075. ; 40
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Journal article (peer-reviewed)abstract
- Streptococcus agalactiae, also known as group B Streptococcus (GBS), is the major cause of neonatal sepsis in humans. A critical step to infection is adhesion of bacteria to epithelial surfaces. GBS adhesins have been identified to bind extracellular matrix components and cellular receptors. However, several putative adhesins have no host binding partner characterised. We report here that surface-expressed β protein of GBS binds to human CEACAM1 and CEACAM5 receptors. A crystal structure of the complex showed that an IgSF domain in β represents a novel Ig-fold subtype called IgI3, in which unique features allow binding to CEACAM1. Bioinformatic assessment revealed that this newly identified IgI3 fold is not exclusively present in GBS but is predicted to be present in adhesins from other clinically important human pathogens. In agreement with this prediction, we found that CEACAM1 binds to an IgI3 domain found in an adhesin from a different streptococcal species. Overall, our results indicate that the IgI3 fold could provide a broadly applied mechanism for bacteria to target CEACAMs.
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| 2. |
- Aksyutina, Yuliya, 1983, et al.
(author)
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Properties of the 7He ground state from 8He neutron knockout
- 2009
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In: Physics Letters B. - : Elsevier BV. - 0370-2693. ; 679:3, s. 191-196
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Journal article (peer-reviewed)abstract
- The unbound nucleus 7He, produced in neutron-knockout reactions with a 240 MeV/u 8He beam in a liquid-hydrogen target, has been studied in an experiment at the ALADIN-LAND setup at GSI. From an R-matrix analysis the resonance parameters for 7He as well as the spectroscopic factor for the 6He(0+) + n configuration in its ground-state have been obtained. The spectroscopic factor is 0.61 confirming that 7He is not a pure single-particle state. An analysis of 5He data from neutron-knockout reactions of 6He in a carbon target reveals the presence of an s-wave component at low energies in the α+n relative energy spectrum. A possible low-lying exited state in 7He observed in neutron knockout data from 8He in a carbon target and tentatively interpreted as a Iπ=1/2− state, could not be observed in the present experiment. Possible explanations of the shape difference between the 7He resonance obtained in the two knockout reactions are discussed in terms of target-dependence or different reaction mechanisms at relativistic energies.
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| 3. |
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| 4. |
- Alrifaiy, Ahmed, et al.
(author)
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A lab-on-a-chip for hypoxic patch clamp measurements combined with optical tweezers and spectroscopy : first investigations of single biological cells
- 2015
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In: Biomedical engineering online. - : Springer Science and Business Media LLC. - 1475-925X. ; 14
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Journal article (peer-reviewed)abstract
- The response and the reaction of the brain system to hypoxia is a vital research subject that requires special instrumentation. With this research subject in focus, a new multifunctional lab-on-a-chip (LOC) system with control over the oxygen content for studies on biological cells was developed. The chip was designed to incorporate the patch clamp technique, optical tweezers and absorption spectroscopy. The performance of the LOC was tested by a series of experiments. The oxygen content within the channels of the LOC was monitored by an oxygen sensor and verified by simultaneously studying the oxygenation state of chicken red blood cells (RBCs) with absorption spectra. The chicken RBCs were manipulated optically and steered in three dimensions towards a patch-clamp micropipette in a closed microfluidic channel. The oxygen level within the channels could be changed from a normoxic value of 18% O 2 to an anoxic value of 0.0-0.5% O 2. A time series of 3 experiments were performed, showing that the spectral transfer from the oxygenated to the deoxygenated state occurred after about 227 ± 1 s and a fully developed deoxygenated spectrum was observed after 298 ± 1 s, a mean value of 3 experiments. The tightness of the chamber to oxygen diffusion was verified by stopping the flow into the channel system while continuously recording absorption spectra showing an unchanged deoxygenated state during 5400 ± 2 s. A transfer of the oxygenated absorption spectra was achieved after 426 ± 1 s when exposing the cell to normoxic buffer. This showed the long time viability of the investigated cells. Successful patching and sealing were established on a trapped RBC and the whole-cell access (Ra) and membrane (Rm) resistances were measured to be 5.033 ± 0.412 M Ω and 889.7 ± 1.74 M Ω respectively.
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| 5. |
- Alrifaiy, Ahmed, et al.
(author)
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Development of microfluidic system and optical tweezers for electrophysiological investigations of an individual cell
- 2010
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In: Optical Trapping and Optical Micromanipulation VII. - Bellingham, Wash : SPIE - The International Society for Optics and Photonics. - 9780819482587
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Conference paper (peer-reviewed)abstract
- We present a new approach of combining Lab-on-a-chip technologies with optical manipulation technique for accurate investigations in the field of cell biology. A general concept was to develop and combine different methods to perform advanced electrophysiological investigations of an individual living cell under optimal control of the surrounding environment. The conventional patch clamp technique was customized by modifying the open system with a gas-tight multifunctional microfluidics system and optical trapping technique (optical tweezers).The system offers possibilities to measure the electrical signaling and activity of the neuron under optimum conditions of hypoxia and anoxia while the oxygenation state is controlled optically by means of a spectroscopic technique. A cellbased microfluidics system with an integrated patch clamp pipette was developed successfully. Selectively, an individual neuron is manipulated within the microchannels of the microfluidic system under a sufficient control of the environment. Experiments were performed to manipulate single yeast cell and red blood cell (RBC) optically through the microfluidics system toward an integrated patch clamp pipette. An absorption spectrum of a single RCB was recorded which showed that laser light did not impinge on the spectroscopic spectrum of light. This is promising for further development of a complete lab-on-a-chip system for patch clamp measurements.
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| 6. |
- Alrifaiy, Ahmed, et al.
(author)
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Ett mikroflödessystem för multipla undersökningar av enstaka biologiska celler under hypoxiska förhållanden
- 2011
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Conference paper (peer-reviewed)abstract
- Introduktion: Syftet med studien är att studera enstaka nervcellers respons vid syrebrist i ett mikroflödessystem för att förstå nervcellens respons vid stroke. Målet med studien var att utveckla ett slutet mikroflödessystem som ger optimal kontroll av den omgivande miljön och samtidigt möjliggöra elektrofysiologiska undersökningar under kontrollerade syreförhållande. Material och metoder: Mikroflödescellen utvecklades för ett inverterat mikroskop, utrustad med en optisk pincett och optisk spektroskopi samt patch-clamp för elektrofysiologiska studier på en enstaka nervcell. Istället för att föra en pipett mot en cell i ett öppet system fångades en enskild cell optiskt i ett slutet mikroflödessystem och fördes mot en fixerad patch-clamp mikropipett. Cellen utsattes för olika syrehalter och övervakades av ett UV-Vis spektroskop medan cellens elektrofysiologiska aktivitet registreras med patch-clamp. Det slutna mikroflödessystemet med integrerad mikropipett, kopplades till ett pumpsystem för införandet av celler och buffert med olika kemiska egenskaper och syrehalter. I ett inverterat mikroskop integrerades optisk pincett, UV-Vis spektrometer och patch-clamp. Resultat och diskussion: För att pröva konceptet fångades och fördes en röd blodcell optiskt mot mikropipetten som befann sig på en fast position i mikroflödescellen. Cellens syrebindningstillstånd varierades genom att tillsätta syrefri eller syresatt buffert och registrerades med UV-Vis spektrometern. I ett vidare experiment manipulerades en nervcell optiskt i ett öppet system mot patch-clamp pipetten och elektrofysiologiska mätningar utfördes. Vi kunde verifiera att den optiska pincetten inte påverkade den elektrofysiologiska mätningen. För närvarandet utförs elektrofysiologiska mätningar i det slutna mikroflödessystemet för att se hur nervcellerna reagerar under varierande syrehalt. Genom mätningarna hoppas vi att få mer kunskap om försvarsmekanismerna som igångsätts av neuroner under syrefattiga förhållanden.
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| 7. |
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| 8. |
- Alrifaiy, Ahmed, et al.
(author)
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Hypoxia on a chip - a novel approach for patch-clamp studies in a microfluidic system with full oxygen control
- 2012
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In: World Congress on Medical Physics and Biomedical Engineering, May 26-31, 2012, Beijing, China. - Berlin : Encyclopedia of Global Archaeology/Springer Verlag. - 9783642293047 - 9783642293054 ; , s. 313-316
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Conference paper (peer-reviewed)abstract
- A new approach to perform patch-clamp experiments on living cells under controlled anoxic and normoxic conditions was developed and tested. To provide an optimal control over the oxygen content and the biochemical environment a patch-clamp recording micropipette was integrated within an oxygen tight poly-methyl methacrylate (PMMA) based microchip. The oxygen content within the microfluidic chamber surrounding patch-clamp micropipette was maintained at 0.5-1.5 % by a continuous flow of artificial extracellular solution purged with nitrogen. The nerve and glial cells acutely obtained from the male rat brain were trapped by the optical tweezers and steered towards the patch-clamp micropipette through the channels of the microchip in order to achieve a close contact between the pipette and the cellular membrane. The patch-clamp recordings revealed that optical tweezers did not affect the electrophysiological properties of the tested cells suggesting that optical trapping is a safe and non-traumatizing method to manipulate living cells in the microfluidic system. Thus, our approach of combining optical tweezers and a gas-tight microfluidic chamber may be applied in various electrophysiological investigations of single cells were optimal control of the experimental conditions and the sample in a closed environment are necessary.
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