| 1. |
- Bibow, Stefan, et al.
(författare)
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Solution structure of discoidal high-density lipoprotein particles with a shortened apolipoprotein A-I.
- 2017
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Ingår i: Nature Structural & Molecular Biology. - : Springer Science and Business Media LLC. - 1545-9993 .- 1545-9985. ; 24:2, s. 187-193
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Tidskriftsartikel (refereegranskat)abstract
- High-density lipoprotein (HDL) particles are cholesterol and lipid transport containers. Mature HDL particles destined for the liver develop through the formation of intermediate discoidal HDL particles, which are the primary acceptors for cholesterol. Here we present the three-dimensional structure of reconstituted discoidal HDL (rdHDL) particles, using a shortened construct of human apolipoprotein A-I, determined from a combination of nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) and transmission electron microscopy (TEM) data. The rdHDL particles feature a protein double belt surrounding a lipid bilayer patch in an antiparallel fashion. The integrity of this structure is maintained by up to 28 salt bridges and a zipper-like pattern of cation-π interactions between helices 4 and 6. To accommodate a hydrophobic interior, a gross 'right-to-right' rotation of the helices after lipidation is necessary. The structure reflects the complexity required for a shuttling container to hold a fluid lipid or cholesterol interior at a protein:lipid ratio of 1:50.
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| 2. |
- Chi N, Celestine, 1978-, et al.
(författare)
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A Structural Ensemble for the Enzyme Cyclophilin Reveals an Orchestrated Mode of Action at Atomic Resolution.
- 2015
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 54:40, s. 11657-61
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Tidskriftsartikel (refereegranskat)abstract
- For enzyme activity, an exact structural and motional orchestration of the active site and its surroundings is believed to be key. In order to reveal such possible phenomena at atomic resolution on the basis of experimental evidence, an experimental restraint driven two-state ensemble of the prototypical enzyme cyclophilin was determined by using a recently introduced exact NOE approach. The ensemble description reveals the presence of an open and a closed state of cyclophilin, which is indicative of large-scale correlated motion. In the open state, the catalytic site is preorganized for catalysis, thus suggesting the mechanism of action to be conformational sampling, while the ligand-binding loop appears to act through an induced fit mechanism. This finding is supported by affinity measurements of a cyclophilin designed to be more open. Overall, more than 60-70 % of the side-chain conformations of cyclophilin appear to be correlated.
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| 3. |
- Vögeli, Beat, et al.
(författare)
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Enzyme Selectivity Fine-Tuned through Dynamic Control of a Loop.
- 2016
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Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:9, s. 3096-100
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Tidskriftsartikel (refereegranskat)abstract
- Allostery has been revealed as an essential property of all proteins. For enzymes, shifting of the structural equilibrium distribution at one site can have substantial impacts on protein dynamics and selectivity. Promising sites of remotely shifting such a distribution by changing the dynamics would be at flexible loops because relatively large changes may be achieved with minimal modification of the protein. A ligand-selective change of binding affinity to the active site of cyclophilin is presented involving tuning of the dynamics of a highly flexible loop. Binding affinity is increased upon substitution of double Gly to Ala at the hinge regions of the loop. Quenching of the motional amplitudes of the loop slightly rearranges the active site. In particular, key residues for binding Phe60 and His126 adopt a more fixed orientation in the bound protein. Our system may serve as a model system for studying the effects of various time scales of loop motion on protein function tuned by mutations.
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