title: Heparin and Methionine Oxidation Promote the Formation of Apolipoprotein A-I Amyloid Comprising α-Helical and β-Sheet Structures.
abstract: Peptides derived from apolipoprotein A-I (apoA-I), the main component of high-density lipoprotein (HDL), constitute the main component of amyloid deposits that colocalize with atherosclerotic plaques. Here we investigate the molecular details of full-length, lipid-deprived apoA-I after assembly into insoluble aggregates under physiologically relevant conditions known to induce aggregation in vitro. Unmodified apoA-I is shown to remain soluble at pH 7 for at least 3 days, retaining its native α-helical-rich structure. Upon acidification to pH 4, apoA-I rapidly assembles into insoluble nonfibrillar aggregates lacking the characteristic cross-β features of amyloid. In the presence of heparin, the rate and thioflavin T responsiveness of the aggregates formed at pH 4 increase and short amyloid-like fibrils are observed, which give rise to amyloid-characteristic X-ray reflections at 4.7 and 10 Å. Solid-state nuclear magnetic resonance (SSNMR) and synchrotron radiation circular dichroism spectroscopy of fibrils formed in the presence of heparin show they retain some α-helical characteristics together with new β-sheet structures. Interestingly, SSNMR indicates a similar molecular structure of aggregates formed in the absence of heparin at pH 6 after oxidation of the three methionine residues, although their morphology is rather different from that of the heparin-derived fibrils. We propose a model for apoA-I aggregation in which perturbations of a four-helix bundle-like structure, induced by interactions of heparin or methionine oxidation, cause the partially helical N-terminal residues to disengage from the remaining, intact helices, thereby allowing self-assembly via β-strand associations.
authors.affiliation: Department of Chemistry, Lancaster University , Lancaster LA1 4YB, United Kingdom.
authors.forename: David
authors.initials: D
authors.lastname: Townsend
authors.affiliation: Department of Chemistry, Lancaster University , Lancaster LA1 4YB, United Kingdom.
authors.forename: Eleri
authors.initials: E
authors.lastname: Hughes
authors.affiliation: Diamond Light Source Ltd. , Diamond House, Harwell Science & Innovation Campus, Didcot OX11 0DE, Oxon, England.
authors.forename: Rohanah
authors.initials: R
authors.lastname: Hussain
authors.affiliation: Diamond Light Source Ltd. , Diamond House, Harwell Science & Innovation Campus, Didcot OX11 0DE, Oxon, England.
authors.forename: Giuliano
authors.initials: G
authors.lastname: Siligardi
authors.affiliation: Department of Chemistry, Lancaster University , Lancaster LA1 4YB, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Baldock
authors.affiliation: Department of Biochemistry, Institute of Integrative Biology, University of Liverpool , Liverpool, United Kingdom.
authors.forename: Jillian
authors.initials: J
authors.lastname: Madine
authors.affiliation: Department of Chemistry, Lancaster University , Lancaster LA1 4YB, United Kingdom.
authors.forename: David A
authors.identifier: 0000-0002-3227-7632
authors.initials: DA
authors.lastname: Middleton
mesh_terms: D058227:Amyloidogenic Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D016632:Apolipoprotein A-I / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D052160:Benzothiazoles; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D006493:Heparin / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008715:Methionine / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D066329:Protein Aggregates; D000072756:Protein Conformation, alpha-Helical; D000072757:Protein Conformation, beta-Strand; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D013050:Spectrometry, Fluorescence; D013844:Thiazoles / Q000737:chemistry
chemical_list: C505693:APOA1 protein, human; D058227:Amyloidogenic Proteins; D016632:Apolipoprotein A-I; D052160:Benzothiazoles; D066329:Protein Aggregates; D011994:Recombinant Proteins; D013844:Thiazoles; C009462:thioflavin T; D006493:Heparin; D008715:Methionine; D006861:Hydrogen Peroxide