title: Comparisons with amyloid-β reveal an aspartate residue that stabilizes fibrils of the aortic amyloid peptide medin.
abstract: Aortic medial amyloid (AMA) is the most common localized human amyloid, occurring in virtually all of the Caucasian population over the age of 50. The main protein component of AMA, medin, readily assembles into amyloid-like fibrils in vitro. Despite the prevalence of AMA, little is known about the self-assembly mechanism of medin or the molecular architecture of the fibrils. The amino acid sequence of medin is strikingly similar to the sequence of the Alzheimer disease (AD) amyloid-β (Aβ) polypeptides around the structural turn region of Aβ, where mutations associated with familial, early onset AD, have been identified. Asp(25) and Lys(30) of medin align with residues Asp(23) and Lys(28) of Aβ, which are known to form a stabilizing salt bridge in some fibril morphologies. Here we show that substituting Asp(25) of medin with asparagine (D25N) impedes assembly into fibrils and stabilizes non-cytotoxic oligomers. Wild-type medin, by contrast, aggregates into β-sheet-rich amyloid-like fibrils within 50 h. A structural analysis of wild-type fibrils by solid-state NMR suggests a molecular repeat unit comprising at least two extended β-strands, separated by a turn stabilized by a Asp(25)-Lys(30) salt bridge. We propose that Asp(25) drives the assembly of medin by stabilizing the fibrillar conformation of the peptide and is thus reminiscent of the influence of Asp(23) on the aggregation of Aβ. Pharmacological comparisons of wild-type medin and D25N will help to ascertain the pathological significance of this poorly understood protein.
authors.affiliation: From the Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom and.
authors.forename: Hannah A
authors.initials: HA
authors.lastname: Davies
authors.affiliation: From the Institute of Integrative Biology, University of Liverpool, Crown Street, Liverpool L69 7ZB, United Kingdom and.
authors.forename: Jillian
authors.initials: J
authors.lastname: Madine
authors.affiliation: the Department of Chemistry, Lancaster University, Lancaster LA1 4YB, United Kingdom d.middleton@lancaster.ac.uk.
authors.forename: David A
authors.initials: DA
authors.lastname: Middleton
mesh_terms: D000595:Amino Acid Sequence; D000954:Antigens, Surface / Q000737:chemistry / Q000378:metabolism*; D001011:Aorta / Q000378:metabolism*; D001224:Aspartic Acid / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D006801:Humans; D008894:Milk Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
chemical_list: D000954:Antigens, Surface; C098942:MFGE8 protein, human; D008894:Milk Proteins; D001224:Aspartic Acid
keywords: Amyloid; Amyloid-beta (AB); Dipolar Assisted Rotational Resonance; Homology Modeling; Protein Misfolding; Protein Structure; Rotational Echo Double Resonance; Salt Bridge; Site-directed Mutagenesis; Solid-state NMR