| 1. |
- Björling, Alexander, 1983, et al.
(författare)
-
Ubiquitous Structural Signaling in Bacterial Phytochromes
- 2015
-
Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 6:17, s. 3379-3383
-
Tidskriftsartikel (refereegranskat)abstract
- The phytochrome family of light-switchable proteins has long been studied by biochemical, spectroscopic and crystallographic means, while a direct probe for global conformational signal propagation has been lacking. Using solution X-ray scattering, we find that the photosensory cores of several bacterial phytochromes undergo similar large-scale structural changes upon red-light excitation. The data establish that phytochromes with ordinary and inverted photocycles share a structural signaling mechanism and that a particular conserved histidine, previously proposed to be involved in signal propagation, in fact tunes photoresponse.
|
|
| 2. |
- Brändén, Gisela, 1975, et al.
(författare)
-
Coherent diffractive imaging of microtubules using an X-ray laser.
- 2019
-
Ingår i: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray free electron lasers (XFELs) create new possibilities for structural studies of biological objects that extend beyond what is possible with synchrotron radiation. Serial femtosecond crystallography has allowed high-resolution structures to be determined from micro-meter sized crystals, whereas single particle coherent X-ray imaging requires development to extend the resolution beyond a few tens of nanometers. Here we describe an intermediate approach: the XFEL imaging of biological assemblies with helical symmetry. We collected X-ray scattering images from samples of microtubules injected across an XFEL beam using a liquid microjet, sorted these images into class averages, merged these data into a diffraction pattern extending to 2 nm resolution, and reconstructed these data into a projection image of the microtubule. Details such as the 4 nm tubulin monomer became visible in this reconstruction. These results illustrate the potential of single-molecule X-ray imaging of biological assembles with helical symmetry at room temperature.
|
|
| 3. |
- Dods, Robert, 1989, et al.
(författare)
-
From Macrocrystals to Microcrystals: A Strategy for Membrane Protein Serial Crystallography.
- 2017
-
Ingår i: Structure. - : Elsevier BV. - 1878-4186 .- 0969-2126. ; 25:9, s. 1461-1468
-
Tidskriftsartikel (refereegranskat)abstract
- Serial protein crystallography was developed at X-ray free-electron lasers (XFELs) and is now also being applied at storage ring facilities. Robust strategies for the growth and optimization of microcrystals are needed to advance the field. Here we illustrate a generic strategy for recovering high-density homogeneous samples of microcrystals starting from conditions known to yield large (macro) crystals of the photosynthetic reaction center of Blastochloris viridis (RCvir). We first crushed these crystals prior to multiple rounds of microseeding. Each cycle of microseeding facilitated improvements in the RCvir serial femtosecond crystallography (SFX) structure from 3.3-Å to 2.4-Å resolution. This approach may allow known crystallization conditions for other proteins to be adapted to exploit novel scientific opportunities created by serial crystallography.
|
|
| 4. |
- Dods, Robert, 1989, et al.
(författare)
-
Ultrafast structural changes within a photosynthetic reaction centre.
- 2021
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 1476-4687 .- 0028-0836. ; 589:7841, s. 310-314
-
Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic reaction centres harvest the energy content of sunlight by transporting electrons across an energy-transducing biological membrane. Here we use time-resolved serial femtosecond crystallography1 using an X-ray free-electron laser2 to observe light-induced structural changes in the photosynthetic reaction centre of Blastochloris viridis on a timescale of picoseconds. Structural perturbations first occur at the special pair of chlorophyll molecules of the photosynthetic reaction centre that are photo-oxidized by light. Electron transfer to the menaquinone acceptor on the opposite side of the membrane induces a movement of this cofactor together with lower amplitude protein rearrangements. These observations reveal how proteins use conformational dynamics to stabilize the charge-separation steps of electron-transfer reactions.
|
|
| 5. |
- Arnlund, David, et al.
(författare)
-
Visualizing a protein quake with time-resolved X-ray scattering at a free-electron laser
- 2014
-
Ingår i: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 11:9, s. 923-926
-
Tidskriftsartikel (refereegranskat)abstract
- We describe a method to measure ultrafast protein structural changes using time-resolved wide-angle X-ray scattering at an X-ray free-electron laser. We demonstrated this approach using multiphoton excitation of the Blastochloris viridis photosynthetic reaction center, observing an ultrafast global conformational change that arises within picoseconds and precedes the propagation of heat through the protein. This provides direct structural evidence for a 'protein quake': the hypothesis that proteins rapidly dissipate energy through quake-like structural motions.
|
|
| 6. |
- Berntsen, Peter, 1974, et al.
(författare)
-
Biomechanical effects of environmental and engineered particles on human airway smooth muscle cells
- 2010
-
Ingår i: Journal of the Royal Society Interface. - : The Royal Society. - 1742-5689 .- 1742-5662. ; 7:Suppl 3, s. S331-S340
-
Tidskriftsartikel (refereegranskat)abstract
- The past decade has seen significant increases in combustion-generated ambient particles, which contain a nanosized fraction (less than 100 nm), and even greater increases have occurred in engineered nanoparticles (NPs) propelled by the booming nanotechnology industry. Although inhalation of these particulates has become a public health concern, human health effects and mechanisms of action for NPs are not well understood. Focusing on the human airway smooth muscle cell, here we show that the cellular mechanical function is altered by particulate exposure in a manner that is dependent upon particle material, size and dose. We used Alamar Blue assay to measure cell viability and optical magnetic twisting cytometry to measure cell stiffness and agonist-induced contractility. The eight particle species fell into four categories, based on their respective effect on cell viability and on mechanical function. Cell viability was impaired and cell contractility was decreased by (i) zinc oxide (40-100 nm and less than 44 mu m) and copper(II) oxide (less than 50 nm); cell contractility was decreased by (ii) fluorescent polystyrene spheres (40 nm), increased by (iii) welding fumes and unchanged by (iv) diesel exhaust particles, titanium dioxide (25 nm) and copper(II) oxide (less than 5 mu m), although in none of these cases was cell viability impaired. Treatment with hydrogen peroxide up to 500 mu M did not alter viability or cell mechanics, suggesting that the particle effects are unlikely to be mediated by particle-generated reactive oxygen species. Our results highlight the susceptibility of cellular mechanical function to particulate exposures and suggest that direct exposure of the airway smooth muscle cells to particulates may initiate or aggravate respiratory diseases.
|
|
| 7. |
- Berntsen, Peter, 1974, et al.
(författare)
-
Dielectric and calorimetric studies of hydrated purple membrane
- 2005
-
Ingår i: Biophysical Journal. - : Elsevier BV. - 0006-3495 .- 1542-0086. ; 89:5, s. 3111-3128
-
Tidskriftsartikel (refereegranskat)abstract
- Purple membranes (PM) from halobacteria were hydrated to ∼0.4 and ∼0.2 g H 2 O/g of PM and studied by dielectric spectroscopy and differential scanning calorimetry between 120 and 300 K. The dielectric process, attributed to a local (β) relaxation of the confined supercooled water, shows an Arrhenius temperature behavior at low temperatures. In the case of the most hydrated PM a small deviation from the Arrhenius behavior occurs at 190-200 K together with a pronounced endothermic process and an increased activation energy. The observed crossover is accompanied by a reduction of the interlayer spacing due to the partial loss of the intermembrane water. All these effects at ∼200 K are consistent with a scenario where the local relaxation process merges with a nonobservable α-relaxation of the interlayer water, giving rise to a more liquid-like behavior of the interfacial water. For the less hydrated sample the effects are less pronounced and shift to a slightly higher temperature. © 2005 by the Biophysical Society.
|
|
| 8. |
- Berntsen, Peter, 1974
(författare)
-
Dynamics of biological membranes and associated water.
- 2008
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An ingenious assembly of biomolecules and water constitute what we call biological tissue. The presence of water in this assembly is fundamental for the physiological processes and can make the difference between life and death. This thesis is concerned with fundamental questions related to the dynamics of water and its presence around all living cells. The cell is surrounded by a membrane that not only serve as a covering, within which the cell can function, but also by means of transport for life essential species. The capacity of membrane to cooperate with its surrounding is life essential and made possible by to proteins and polar lipids, essentially phospholipids that make the membranes soft. Phospholipids are so called amphipathic molecules, i.e. they have a hydrophobic part (repels water) and a hydrophilic (water loving) part. The hydrophilic region is usually referred to as the head group, and the hydrophobic part is known as the tails. The amphipathic character of the phospholipidsenable them to form lamellar structures called bilayers. In this work hundreds of parallell lipid bilayers on a surface have served as our model system. One bilayer is composed of two layers of lipids arranged so that their hydrocarbon tails face one another, while their charged head groups face the water on either side of the bilayer. We have studied the influence of water in two different membrane systems. One is naturally existing in the plasma membrane of Halobacterium salinarum, which is a bacterium that lives in extremely salty conditions. The other membrane system we have used is from the lecithin group of lipids whose lipid head is made of the alcohol choline (CH3)3N+CH2CH2OH. The lecithins are involved in the transport of other lipids and exist abundantly in the liver and in egg yolk.At biological temperatures there is a mix of many fast and slow motions which makes it diffcult to find out different motions and their possible interrelations. For moderate hydration levels there is no crystallization of the water within the lipid bilayers (not even at temperaures as low as 80K), however there is a substantial slowing-down of the dynamics with decreasing temperature and below a certain temperature the lipids are frozen in a glassy phase. Starting at such low temperatures the onset of different motions of the water and in the lipid systems were probed at successively higher temperatures by using broadband dielectric spectroscopy, differential scanning calorimetry and quasielastic neutron scattering. We found that the molecular motions of the lipids is similar to the molecular motions of glass forming liquids at low temperatures and this behavior was dependent on the amount of water in the lipid system. Transport of charge carriers was also found to be strongly dependent on the water content and this charge transport was changed at the gel-to-liquid transition of the lipids. Furthermore, it was shown that already at 120K (−153◦C) there is local fast motions of the lipid tails, that should be independent of the water content. This work highlights a complex cooperation between water activity and motions in membranes. By shedding light on the coupling between water and membrane motions new insights into the role of water for membrane properties can be gained.
|
|
| 9. |
- Berntsen, Peter, 1974
(författare)
-
Dynamics of Biomembranes and Rheological Properties of Living Cells
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An ingenious assembly of biomolecules and water constitute what we call biological tissue. The presence of water in this assembly is fundamental for the physiological processes and can make the difference between life and death. One of the hallmark features of cellular life is the presence of membranes that separates the cell from the rest of the world and its compartments from each other. There is, however, some fluidity through the membranes. This fluid environment is possible due to the presence of water. The close association and dynamical interplay between lipid membranes and the surrounding water is investigated in the first part of this work. Membranes and water constitute important parts in the macromolecular assemblies and architecture that builds the whole living cell. Cells are highly dynamic with internal structures that constantly remodels and respond to external forces like a viscoelastic material. In many critical biological processes, cells both exert and respond to forces in their surroundings; the mechanical and rheological properties of cells are intimately related to their viscoelastic character which is the topic of the second part of this work. At biological temperatures there is a mix of many types of motions occurring on similar time scales which makes it difficult to separate different motions and elucidate interrelations. However, at low temperatures the different dynamical processes occur on considerably more separated time scales, which simplifies the analysis. Starting at low temperatures the onset of different motions of the water and the lipids were probed at successively higher temperatures by using broadband dielectric spectroscopy, differential scanning calorimetry and quasielastic neutron scattering. We found that the molecular motions of the lipids are similar to the molecular motions of glass forming liquids at low temperatures and the exact dynamical behavior was strongly dependent on the amount of water in the lipid system. The hydration water in lipid membranes modulates the motions of the lipid head groups and vice-versa there are also local lipid motions that influence the water dynamics at low hydration levels. Thus, in lipid membranes there is a strong interplay between water and lipid dynamics.The rheological properties of living cells were probed with optical magnetic twisting cytometry. The results show that the cellular mechanical function is susceptible to particulate exposure, and that the structural relaxation time is faster by nearly a factor 10, but also less temperature dependent close to the membrane compared to in the interior cytoskeletal structures. Moreover, for ATP depleted cells the relaxation dynamics slows down around physiological temperatures, which indicates the importance of ATP hydrolysis for the cellular relaxation dynamics.
|
|
| 10. |
- Berntsen, Peter, 1974, et al.
(författare)
-
Interplay between Hydration Water and Headgroup Dynamics in Lipid Bilayers
- 2011
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 115:8, s. 1825-1832
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the interplay between water and lipid dynamics has been investigated by broadband dielectric spectroscopy and modulated differential scanning calorimetry (MDSC). The rnultilamellar lipid bilayer system 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) has been studied over a broad temperature range at three different water contents: about 3, 6, and 9 water molecules per lipid molecule. The results from the dielectric relaxation measurements show that at temperatures
|
|
