| 1. |
- Aisenbrey, Christopher, et al.
(författare)
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Helix orientations in membrane-associated Bcl-XL determined by 15N-solid-state NMR spectroscopy
- 2007
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Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 37:1, s. 71-80
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Tidskriftsartikel (refereegranskat)abstract
- Controlled cell death is fundamental to tissue hemostasis and apoptosis malfunctions can lead to a wide range of diseases. Bcl-xL is an anti-apoptotic protein the function of which is linked to its reversible interaction with mitochondrial outer membranes. Its interfacial and intermittent bilayer association makes prediction of its bound structure difficult without using methods able to extract data from dynamic systems. Here we investigate Bcl-xL associated with oriented lipid bilayers at physiological pH using solid-state NMR spectroscopy. The data are consistent with a C-terminal transmembrane anchoring sequence and an average alignment of the remaining helices, i.e. including helices 5 and 6, approximately parallel to the membrane surface. Data from several biophysical approaches confirm that after removal of the C-terminus from Bcl-xL its membrane interactions are weak. In the presence of membranes Bcl-xL can still interact with a Bak BH3 domain peptide suggesting a model where the hydrophobic C-terminus of the protein unfolds and inserts into the membrane. During this conformational change the Bcl-xL hydrophobic binding pocket becomes accessible for protein–protein interactions whilst the structure of the N-terminal region remains intact.
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| 2. |
- Aisenbrey, Christopher, et al.
(författare)
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Macromolecular Crowding at Membrane Interfaces : Adsorption and Alignment of Membrane Peptides
- 2008
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Ingår i: Journal of Molecular Biology. - : Elsevier. - 0022-2836 .- 1089-8638. ; 375, s. 376-385
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Tidskriftsartikel (refereegranskat)abstract
- Association of proteins to cellular membranes is involved in various biological processes. Various theoretical models have been developed to describe this adsorption mechanism, commonly implying the concept of an ideal solution. However, due to the two-dimensional character of membrane surfaces intermolecular interactions between the adsorbed molecules become important. Therefore previously adsorbed molecules can influence the adsorption behavior of additional protein molecules and their membrane-associated structure. Using the model peptide LAH4, which upon membrane-adsorption can adopt a transmembrane as well as an in-planar configuration, we carried out a systematic study of the correlation between the peptide concentration in the membrane and the topology of this membrane-associated polypeptide. We could describe the observed binding behavior by establishing a concept, which includes intermolecular interactions in terms of a scaled particle theory.High surface concentration of the peptide shifts the molecules from an in-planar into a transmembrane conformation, a process driven by the reduction of occupied surface area per molecule. In a cellular context, the crowding-dependent alignment might provide a molecular switch for a cell to sense and control its membrane occupancy. Furthermore, crowding might have pronounced effects on biological events, such as the cooperative behavior of antimicrobial peptides and the membrane triggered aggregation of amyloidogenic peptides.
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| 3. |
- Aisenbrey, Christopher, et al.
(författare)
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Specific Isotope Labeling of Colicin E1 and B Channel Domains For Membrane Topological Analysis by Oriented Solid-State NMR Spectroscopy
- 2008
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Ingår i: ChemBioChem. - : Wiley-VCH Verlagsgesellschaft. - 1439-4227 .- 1439-7633. ; 9:6, s. 944-951
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Tidskriftsartikel (refereegranskat)abstract
- An approach is presented to selectively label the methionines of the colicin E1 and B channel domains, each about 200 residues in size, and use them for oriented solid-state NMR investigations. By combining site-directed mutagenesis, bacterial overexpression in a methionine auxotroph E. coli strain and biochemical purification, quantitative amounts of the proteins for NMR structural investigations were obtained. The proteins were selectively labeled with 15N at only one, or at a few, selected sites. Multidimensional heteronuclear correlation high-resolution NMR spectroscopy and mass spectrometry were used to monitor the quality of isotopic labeling. Thereafter the proteins were reconstituted into oriented phospholipid bilayers and investigated by proton-decoupled 15N solid-state NMR spectroscopy. The colicin E1 thermolytic fragment that carries a single 15N methionine within its hydrophobic helix 9 region exhibited 15N resonances that are characteristic of helices that are oriented predominantly parallel to the membrane surface at low temperature, and a variety of alignments and conformations at room temperature. This suggests that the protein can adopt both umbrella and pen-knife conformations.
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| 4. |
- Aisenbrey, Christopher, et al.
(författare)
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Structure and dynamics of membrane-associated ICP47, a viral inhibitor of the MHC I antigen-processing machinery
- 2006
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Ingår i: The Journal of Biological Chemistry. - 0021-9258. ; 281:41, s. 30365-72
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Tidskriftsartikel (refereegranskat)abstract
- To evade the host's immune response, herpes simplex virus employs the immediate early gene product ICP47 (IE12) to suppress antigen presentation to cytotoxic T-lymphocytes by inhibition of the ATP-binding cassette transporter associated with antigen processing (TAP). ICP47 is a membrane-associated protein adopting an alpha-helical conformation. Its active domain was mapped to residues 3-34 and shown to encode all functional properties of the full-length protein. The active domain of ICP47 was reconstituted into oriented phospholipid bilayers and studied by proton-decoupled 15N and 2H solid-state NMR spectroscopy. In phospholipid bilayers, the protein adopts a helix-loop-helix structure, where the average tilt angle of the helices relative to the membrane surface is approximately 15 degrees (+/- 7 degrees ). The alignment of both structured domains exhibits a mosaic spread of approximately 10 degrees . A flexible dynamic loop encompassing residues 17 and 18 separates the two helices. Refinement of the experimental data indicates that helix 1 inserts more deeply into the membrane. These novel insights into the structure of ICP47 represent an important step toward a molecular understanding of the immune evasion mechanism of herpes simplex virus and are instrumental for the design of new therapeutics.
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| 5. |
- Aisenbrey, Christopher, et al.
(författare)
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Structure, dynamics and topology of membrane polypeptides by oriented 2H solid-state NMR spectroscopy
- 2007
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Ingår i: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 36:4-5, s. 451-60
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Tidskriftsartikel (refereegranskat)abstract
- Knowledge of the structure, dynamics and interactions of polypeptides when associated with phospholipid bilayers is key to understanding the functional mechanisms of channels, antibiotics, signal- or translocation peptides. Solid-state NMR spectroscopy on samples uniaxially aligned relative to the magnetic field direction offers means to determine the alignment of polypeptide bonds and domains relative to the bilayer normal. Using this approach the 15N chemical shift of amide bonds provides a direct indicator of the approximate helical tilt, whereas the 2H solid-state NMR spectra acquired from peptides labelled with 3,3,3-2H3-alanines contain valuable complimentary information for a more accurate analysis of tilt and rotation pitch angles. The deuterium NMR line shapes are highly sensitive to small variations in the alignment of the Cα–Cβ bond relative to the magnetic field direction and, therefore, also the orientational distribution of helices relative to the membrane normal. When the oriented membrane samples are investigated with their normal perpendicular to the magnetic field direction, the rate of rotational diffusion can be determined in a semi-quantitative manner and thereby the aggregation state of the peptides can be analysed. Here the deuterium NMR approach is first introduced showing results from model amphipathic helices. Thereafter investigations of the viral channel peptides Vpu1–27 and Influenza A M222–46 are shown. Whereas the 15N chemical shift data confirm the transmembrane helix alignments of these hydrophobic sequences, the deuterium spectra indicate considerable mosaic spread in the helix orientations. At least two peptide populations with differing rotational correlation times are apparent in the deuterium spectra of the viral channels suggesting an equilibrium between monomeric peptides and oligomeric channel configurations under conditions where solid-state NMR structural studies of these peptides have previously been performed.
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