ORCID Profile
0000-0001-8897-8975
Current Organisations
Cristal Therapeutics (Netherlands)
,
Universiteit Maastricht Cardiovascular Research Institute Maastricht
,
Universiteit Utrecht
,
University of Glasgow
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Publisher: Wiley
Date: 14-01-2004
DOI: 10.1002/MRC.1326
Abstract: The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) plays a role in the regulation of the activity of this important ligand-gated ion channel. The lipid composition of the host membrane affects conformational equilibria of the nAChR and several classes of inhibitors, most notably anaesthetics, interact directly or indirectly with the four transmembrane M-segments, M1-M4, of the nAChR subunits. It has proven difficult to gain insight into structure-function relationships of the M-segments in the context of the entire receptor and the biomembrane environment. However, model membrane systems are well suited to obtain detailed information about protein-lipid interactions. In this solid-state NMR study, we characterized interactions between a synthetic alphaM1 segment of the T. californica nAChR and model membranes of different phosphatidylcholine (PC) lipids. The results indicate that alphaM1 interacts strongly with PC bilayers: the peptide orders the lipid acyl chains and induces the formation of small vesicles, possibly through modification of the lateral pressure profile in the bilayer. The multilamellar vesicle morphology was stabilized by the presence of cholesterol, implying that either the rigidity or the bilayer thickness is a relevant parameter for alphaM1-membrane interactions, which also has been suggested for the entire nAChR. Our results suggest that the model systems are to a certain extent sensitive to peptide-bilayer hydrophobic matching requirements, but that the lipid response to hydrophobic mismatch alone is not the explanation. The effect of alphaM1 on different PC bilayers may indicate that the peptide is conformationally flexible, which in turn would support a membrane-mediated modulation of the conformation of transmembrane segments of the nAChR.
Publisher: Elsevier BV
Date: 10-2004
DOI: 10.1016/J.BBAMEM.2004.06.021
Abstract: The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) is predominantly alpha-helical, and of the four distinctly different transmembrane M-segments, only the helicity of M1 is ambiguous. In this study, we have investigated the conformation of a membrane-embedded synthetic M1 segment by solid-state nuclear magnetic resonance (NMR) methods. A 35-residue peptide representing the extended alphaM1 domain 206-240 of the Torpedo californica nAChR was synthesized with specific 13C - and 15N-labelled amino acids, and was incorporated in different phosphatidylcholine model membranes. The chemical shift of the isotopic labels was resolved by magic angle spinning (MAS) NMR and could be related to the secondary structure of the alphaM1 analog at the labelled sites. Our results show that the membrane-embedded alphaM1 segment forms an unstable alpha-helix, particularly near residue Leu18 (alphaLeu223 in the entire nAChR). This non-helical tendency was most pronounced when the peptide was incorporated in fully hydrated phospholipid bilayers, with an estimated 40-50% of the peptides having an extended conformation at position Leu18. We propose that the conserved proline residue at position 16 in the alphaM1 analog imparts a conformational flexibility on the M1 segments that could enable membrane-mediated modulation of nAChR activity.
Publisher: Elsevier BV
Date: 05-2007
DOI: 10.1016/J.JMB.2007.02.063
Abstract: The disruption of intracellular calcium homeostasis plays a central role in the pathology of Alzheimer's disease, which is also characterized by accumulation of the amyloid-beta peptides Abeta40 and Abeta42. These hipathic peptides may become associated with neuronal membranes and affect their barrier function, resulting in the loss of calcium homeostasis. This suggestion has been extensively investigated by exposing protein-free model membranes, either vesicles or planar bilayers, to soluble Abeta. Primarily unstructured Abeta has been shown to undergo a membrane-induced conformational change to either primarily beta-structure or helical structure, depending, among other factors, on the model membrane composition. Association of Abeta renders lipid bilayers permeable to ions but there is dispute whether this is due to the formation of discrete transmembrane ion channels of Abeta peptides, or to a non-specific perturbation of bilayer integrity by lipid head group-associated Abeta. Here, we have attempted incorporation of Abeta in the hydrophobic core of zwitterionic bilayers, the most simple model membrane system, by preparing proteoliposomes by hydration of a mixed film of Abeta peptides and phosphatidylcholine (PC) lipids. Despite the use of a solvent mixture in which Abeta40 and Abeta42 are almost entirely helical, the Abeta analogs were beta-structured in the resulting vesicle dispersions. When Abeta40-containing vesicles were fused into a zwitterionic planar bilayer, the typical irregular "single channel-like" conductance of Abeta was observed. The maximum conductance increased with additional vesicle fusion, while still exhibiting single channel-like behavior. Supported bilayers formed from Abeta40/PC vesicles did not exhibit any channel-like topological features, but the bilayer destabilized in time. Abeta40 was present primarily as beta-sheets in supported multilayers formed from the same vesicles. The combined observations argue for a non-specific perturbation of zwitterionic bilayers by surface association of small hipathic Abeta40 assemblies.
Location: United States of America
Location: United States of America
Location: Netherlands
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Rob Liskamp.