Prof Sonia Antoranz Contera

Abstract:

Relevant parameters for non-covalent protein functionalization of carbon nanotubes are explored. Multiwalled carbon nanotubes are carboxylated and functionalized with metalloproteins. Using atomic force microscopy (AFM) we quantitatively determine that coverage with nitrogen-doped multiwalled carbon nanotubes is superior compared to coverage with un-doped multiwalled carbon nanotubes, due to enhanced carboxylation. Conformational analysis using a combination of AFM, antibody binding assays, circular dichroism and UV-visible spectroscopy demonstrates that the metalloproteins retain their native structure when adsorbed to nitrogen-doped multiwalled carbon nanotubes irrespective of their size, charge or folding motif.

Abstract:

Nitrogen-doped multiwalled carbon nanotubes (CNx MWNTs) have been cut to an average length of ∼1 μm by room-temperature acid treatment. Imaging of the surface morphology of the CNx, MWNTs (x = 2-5%) after sonication in acid or in ethanol (as a control) allowed the relationship between surface structure and acid cutting to be characterized. The effect of the acid treatment on the electrical conductance of the CN x MWNTs was also determined. The conductance of acid-treated CN x MWNTs was found to vary significantly within the sample and to be lower than the value of 1.0 G0 observed for as-produced CS x MWNTs. The G - V curves reported for acid-treated CNx MWNTs had an average slope of 0.19 G0/V, which is significantly smaller than the average of 0.70 G0/V measured for as-produced CNx MWNTs. Acid-treated CNx MWNTs exhibited a more rapid electrical breakdown with larger current steps, indicating the breakdown of several MWNT layers simultaneously. © 2008 American Chemical Society.

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 amphipathic 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 amphipathic Abeta40 assemblies.