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  • 1.
    Nordlund, Gustav
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Membrane-mimetic systems: Novel methods and results from studies of respiratory enzymes2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The processes localized to biological membranes are of great interest, both from a scientific and pharmaceutical point of view. Understanding aspects such as the detailed mechanism and regulation of these processes requires investigation of the structure and function of the membrane-bound proteins in which they take place. The study of these processes is often complicated by the need to create in vitro systems that mimic the environment in which these proteins are normally found in vivo. This thesis describes some of the methods available for membrane-protein studies in membrane-mimetic systems, as well as our work aimed at developing such systems. Furthermore, results from studies using these systems are described.

    In the first two studies, described in Papers I & II, we investigated the use of silica particle-supported lipid bilayers, both for membrane-protein studies and as possible drug-delivery vehicles. Successful reconstitution of a multisubunit proton-pump, cytochrome c oxidase is described and characterized. Initial attempts to develop drug-delivery systems with two different targeting peptides are also described in the thesis.

    The second part of this thesis revolves around our work with membraneprotein dependent pathways. Results from studies of systems where the proton- pump bo3 oxidase and ATP synthase work in concert are described. The results show a surprising lipid-composition dependence for the coupled bo3- ATP-synthase activity (Paper III).

    Finally, a new system utilizing synaptic vesicle-fusion proteins for coreconstitution of membrane proteins is described, showing successful coreconstitution of a small respiratory chain, delivery of soluble proteins to preformed liposomes and reconstitution of ATP synthase in native membranes (Paper IV).

  • 2.
    Nordlund, Gustav
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    von Ballmoos, Christoph
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    SNARE-fusion mediated insertion of membrane proteins into native and artificial membranesManuscript (preprint) (Other academic)
  • 3.
    Nordlund, Gustav
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    von Ballmoos, Christoph
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics. University of Bern, Switzerland.
    SNARE-fusion mediated insertion of membrane proteins into native and artificial membranes2014In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 5, p. 4303-Article in journal (Refereed)
    Abstract [en]

    Membrane proteins carry out functions such as nutrient uptake, ATP synthesis or transmembrane signal transduction. An increasing number of reports indicate that cellular processes are underpinned by regulated interactions between these proteins. Consequently, functional studies of these networks at a molecular level require co-reconstitution of the interacting components. Here, we report a SNARE protein-based method for incorporation of multiple membrane proteins into artificial membrane vesicles of well-defined composition, and for delivery of large water-soluble substrates into these vesicles. The approach is used for in vitro reconstruction of a fully functional bacterial respiratory chain from purified components. Furthermore, the method is used for functional incorporation of the entire F1F0 ATP synthase complex into native bacterial membranes from which this component had been genetically removed. The novel methodology offers a tool to investigate complex interaction networks between membrane-bound proteins at a molecular level, which is expected to generate functional insights into key cellular functions.

  • 4.
    Nordlund, Gustav
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Lönneborg, Rosa
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Formation of supported lipid bilayers on silica particles studied using flow cytometry2009In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 25, no 8, p. 4601-4606Article in journal (Refereed)
    Abstract [en]

    Silica colloidal particles with functionalized surfaces are used, for example, in studies of membrane proteins or for drug delivery, where novel applications are based on the use of particles covered by lipid membrane bilayers. The mechanism by which such supported lipid bilayers are formed on spherical support is not fully understood. Here, we present results from studies of this process using a new method based on flow cytometry. The approach enabled us to detect particle populations coated and uncoated with lipids in the same sample according to the vesicle:particle surface area ratio. The data suggest that DOPC lipid vesicles efficiently break upon interaction with the silica colloidal particle surface; only a small fraction of the adsorbed vesicles remain unbroken. Furthermore, the data support earlier observations showing that formation of the lipid bilayer at the surface is a cooperative process, where bilayer formation is catalyzed by previously bound membrane fragments.

  • 5.
    Nordlund, Gustav
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Ng, Jovice Boon Sing
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    A Membrane-reconstituted Multisubunit Functional Proton Pump on Mesoporous Silica Particles2009In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 3, no 9, p. 2639-2646Article in journal (Refereed)
    Abstract [en]

    We have investigated formation of a proteolipid membrane surrounding mesoporous silica particles with a diameter of 550 nm and pore sizes of 3.0 nm. A multisubunit redox-driven proton pump, cytochrome c oxidase, was incorporated into the membrane and we show that the enzyme is fully functional, both with respect to catalysis of O2 reduction to water, and charge separation across the membrane. The orientation of cytochrome c oxidase in the membrane was found to be the same (~70/30 %) in the lipid vesicles and in the silica-particle supported lipid membrane, which provides information on the mechanism by which the vesicles adsorb to the surface. Furthermore, cytochrome c oxidase could maintain a proton electrochemical gradient across the supported proteomembrane, i.e. the membrane system was proton tight, defining an interior particle compartment that is separated from the surrounding aqueous media. Such a biofunctional cellular interface, supported onto a colloid that has a connected interior cytoskeleton-like pore structure, provides a basis for functional studies of membrane-bound transport proteins, and also for applications within pharmaceutical drug delivery.

  • 6.
    Nordlund, Gustav
    et al.
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Rydström Lundin, Camilla
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Nilsson, Tobias
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    von Ballmoos, Christoph
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Effect of lipid composition on respiration-driven ATP synthesisManuscript (preprint) (Other academic)
    Abstract [en]

    Energy conversion in biological systems is underpinned by membrane-bound proton transporters that generate and maintain a proton electrochemical gradient across the membrane. The free energy stored in this gradient is used, for example, for transport of molecules or ions by other transporters as well as for generation of ATP by the ATP synthase. Understanding the overall process requires functional studies of the coupled reactions, which involve co-reconstitution of e.g. a proton pump and a transporter that utilizes the proton gradient. This process is likely to be further influenced by the composition of the membrane, which, for example, may facilitate lateral proton transfer. In the present study, we have co-reconstituted the proton pump bo3 ubiquinol oxidase with ATP synthase, both from E. coli, in liposomes with different membrane compositions. The coupled proton pumping and ATP-synthesis activities were investigated. We found that the ATP synthesis was significantly higher in a membrane composed of pure DOPC lipids than in the presence of DOPA, DOPE, DOPG or cardiolipin. The drop in activity was considerably more pronounced upon addition of the negatively charged head groups (PA, PG or cardiolipin) than upon addition of the zwitterionic PE. The origin of these effects is discussed.

  • 7. Xia, Yu
    et al.
    Lundbäck, Anna-Karin
    Sahaf, Newsha
    Nordlund, Gustav
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Brzezinski, Peter
    Stockholm University, Faculty of Science, Department of Biochemistry and Biophysics.
    Eshaghi, Said
    Co(2+) Selectivity of Thermotoga maritima CorA and Its Inability to Regulate Mg(2+) Homeostasis Present a New Class of CorA Proteins2011In: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 286, no 18Article in journal (Refereed)
    Abstract [en]

    CorA is a family of divalent cation transporters ubiquitously present in bacteria and archaea. Although CorA can transport both Mg(2+) and Co(2+) almost equally well, its main role has been suggested to be that of primary Mg(2+) transporter of prokaryotes and hence the regulator of Mg(2+) homeostasis. The reason is that the affinity of CorA for Co(2+) is relatively low and thus considered non-physiological. Here, we show that Thermotoga maritima CorA (TmCorA) is incapable of regulating the Mg(2+) homeostasis and therefore cannot be the primary Mg(2+) transporter of T. maritima. Further, our in vivo experiments confirm that TmCorA is a highly selective Co(2+) transporter, as it selects Co(2+) over Mg(2+) at > 100 times lower concentrations. In addition, we present data that show TmCorA to be extremely thermostable in the presence of Co(2+). Mg(2+) could not stabilize the protein to the same extent, even at high concentrations. We also show that addition of Co(2+), but not Mg(2+), specifically induces structural changes to the protein. Altogether, these data show that TmCorA has the role of being the transporter of Co(2+) but not Mg(2+). The physiological relevance and requirements of Co(2+) in T. maritima is discussed and highlighted. We suggest that CorA may have different roles in different organisms. Such functional diversity is presumably a reflection of minor, but important structural differences within the CorA family that regulate the gating, substrate selection, and transport.

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