Using a new method which involves laser lights and fat-coated silver nanoparticles, researchers have been able to catch a glimpse of the amyloid beta molecule as it attempted to bore into the outer covering of a cell decoy.
While the origin of Alzheimer’s Disease is still hotly debated, it is likely that a specific form of the amyloid beta molecule, which is able to attack cell membranes, is a major player. Defeating this molecule would be easier if its shape and form were known better, but that has proven to be a difficult task until now.
“Everybody wants to make the key to solve Alzheimer’s Disease, but we don’t know what the lock looks like. We now have a glimpse of something which could be the lock. May be it’s still not the real thing, but as of now, this is our best bet”, says Sudipta Maiti, who co-directed the efforts with P. K. Madhu (both from TIFR). If they are right, then designing the key, i.e. making a drug molecule which can attack the lock, may be more achievable now.
The lock resembles the shape of a hairpin, but with a twist. Debanjan Bhowmik, the lead contributor of the study says “This has been suspected earlier, but what we found was an unexpected twist in the structure, now becoming a beta-hairpin – very different from the typical hairpin structure people imagined. This may allow these bunch of amyloid beta molecules to form toxic pores in the cell membranes”.
The findings published in the journal ACS Nano this week by a joint team of researchers from the Tata Institute of Fundamental Research, Indian Institute of Science and the University of Toronto, have cracked the problem that has eluded scientists for years, by using a modified version of Raman Spectroscopy.
They studied a tiny laser-induced signal from the amyloid beta which reported their shape. A critical modification in the original Raman Spectroscopy technique allowed the measurement of tiny signals that would otherwise have gone unnoticed. They encased silver nanoparticles in a fat layer (“membrane”) that mimicked the outer membranes of living cells. According to co-author Gilbert Walker, “While the amyloid beta got fooled by it and stuck to the membrane, the silver inside enhanced the signal to a measurable level and acted as a light beacon to reveal the peptide signature”. The technique offers promise for deciphering the shape of many such membrane molecules, some of which may be related to other types of diseases.
Each research team brought something different to the table. As Jaydeep Basu, who led the IISc team, says, “It’s a great example of how contemporary science breaks all barriers to bring people together for the pure love of science and the quest for the unknown!” One hopes that the search for the key to solve Alzheimer’s has taken a step forward with this finding.
Funding: The research was funded by the Indian Department of Biotechnology, International Advanced Research Centre for Powder Metallurgy & New Materials, Indian Department of Science and Technology, Natural Sciences and Engineering Research Council.
Source: Sudipta Maiti – Tata Institute of Fundamental Research
Image Credit: The image is credited to Debanjan Bhowmik/TIFR
Original Research: Abstract for “Cell-Membrane-Mimicking Lipid-Coated Nanoparticles Confer Raman Enhancement to Membrane Proteins and Reveal Membrane-Attached Amyloid-β Conformation” by Debanjan Bhowmik, Kaustubh R. Mote, Christina M. MacLaughlin, Nupur Biswas, Bappaditya Chandra, Jaydeep K. Basu, Gilbert C. Walker, Perunthiruthy K. Madhu, and Sudipta Maiti in ACS Nano. Published online August 25 2015 doi:10.1021/acsnano.5b03175
Cell-Membrane-Mimicking Lipid-Coated Nanoparticles Confer Raman Enhancement to Membrane Proteins and Reveal Membrane-Attached Amyloid-β Conformation
Identifying the structures of membrane bound proteins is critical to understanding their function in healthy and diseased states. We introduce a surface enhanced Raman spectroscopy technique which can determine the conformation of membrane-bound proteins, at low micromolar concentrations, and also in the presence of a substantial membrane-free fraction. Unlike conventional surface enhanced Raman spectroscopy, our approach does not require immobilization of molecules, as it uses spontaneous binding of proteins to lipid bilayer-encapsulated Ag nanoparticles. We apply this technique to probe membrane-attached oligomers of Amyloid-β40 (Aβ40), whose conformation is keenly sought in the context of Alzheimer’s disease. Isotope-shifts in the Raman spectra help us obtain secondary structure information at the level of individual residues. Our results show the presence of a β-turn, flanked by two β-sheet regions. We use solid-state NMR data to confirm the presence of the β-sheets in these regions. In the membrane-attached oligomer, we find a strongly contrasting and near-orthogonal orientation of the backbone H-bonds compared to what is found in the mature, less-toxic Aβ fibrils. Significantly, this allows a “porin” like β-barrel structure, providing a structural basis for proposed mechanisms of Aβ oligomer toxicity.
“Cell-Membrane-Mimicking Lipid-Coated Nanoparticles Confer Raman Enhancement to Membrane Proteins and Reveal Membrane-Attached Amyloid-β Conformation” by Debanjan Bhowmik, Kaustubh R. Mote, Christina M. MacLaughlin, Nupur Biswas, Bappaditya Chandra, Jaydeep K. Basu, Gilbert C. Walker, Perunthiruthy K. Madhu, and Sudipta Maiti in ACS Nano. Published online August 25 2015 doi:10.1021/acsnano.5b03175