title: Cell-Membrane-Mimicking Lipid-Coated Nanoparticles Confer Raman Enhancement to Membrane Proteins and Reveal Membrane-Attached Amyloid-β Conformation.
abstract: 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.
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research , Homi Bhabha Road, Colaba, Mumbai 400005, India.
authors.forename: Debanjan
authors.initials: D
authors.lastname: Bhowmik
authors.affiliation: TIFR Centre for Interdisciplinary Sciences , 21 Brundavan Colony, Narsinghi, Hyderabad 500075, India.
authors.forename: Kaustubh R
authors.initials: KR
authors.lastname: Mote
authors.affiliation: Department of Chemistry, Lash Miller Laboratories, University of Toronto , Toronto, ON M5S 3H6, Canada.
authors.forename: Christina M
authors.initials: CM
authors.lastname: MacLaughlin
authors.affiliation: Department of Physics, Indian Institute of Science , Bengaluru 560012, India.
authors.forename: Nupur
authors.initials: N
authors.lastname: Biswas
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research , Homi Bhabha Road, Colaba, Mumbai 400005, India.
authors.forename: Bappaditya
authors.initials: B
authors.lastname: Chandra
authors.affiliation: Department of Physics, Indian Institute of Science , Bengaluru 560012, India.
authors.forename: Jaydeep K
authors.initials: JK
authors.lastname: Basu
authors.affiliation: Department of Chemistry, Lash Miller Laboratories, University of Toronto , Toronto, ON M5S 3H6, Canada.
authors.forename: Gilbert C
authors.initials: GC
authors.lastname: Walker
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research , Homi Bhabha Road, Colaba, Mumbai 400005, India.|TIFR Centre for Interdisciplinary Sciences , 21 Brundavan Colony, Narsinghi, Hyderabad 500075, India.
authors.forename: Perunthiruthy K
authors.initials: PK
authors.lastname: Madhu
authors.affiliation: Department of Chemical Sciences, Tata Institute of Fundamental Research , Homi Bhabha Road, Colaba, Mumbai 400005, India.
authors.forename: Sudipta
authors.initials: S
authors.lastname: Maiti
mesh_terms: D000544:Alzheimer Disease / Q000378:metabolism* / Q000473:pathology; D016229:Amyloid beta-Peptides / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D008055:Lipids / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008565:Membrane Proteins / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry*; D011487:Protein Conformation; D055503:Protein Multimerization; D013059:Spectrum Analysis, Raman
chemical_list: D016229:Amyloid beta-Peptides; D008051:Lipid Bilayers; D008055:Lipids; D008565:Membrane Proteins
keywords: amyloid beta peptide; lipid SERS; lipid-coated nanoparticles; membrane protein structures; oligomers; solid-state NMR; surface enhanced Raman spectroscopy