title: Hydrogen/Deuterium Exchange and Molecular Dynamics Analysis of Amyloid Fibrils Formed by a D69K Charge-Pair Mutant of Human Apolipoprotein C-II.
abstract: Plasma apolipoproteins form amphipathic α helices in lipid environments but in the lipid-free state show a high propensity to form β structure and self-associate into amyloid fibrils. The widespread occurrence of apolipoproteins in amyloid plaques suggests disease-related roles, specifically in atherosclerosis. To reconcile the dual abilities of apolipoproteins to form either α helices or cross-β sheet structures, we examined fibrils formed by human apolipoprotein C-II (apoC-II). A structural model for apoC-II fibrils shows a cross-β core with parallel β strands, including a buried K30-D69 charge pair. We investigated the effect of abolishing this charge pair in mutant D69K apoC-II. Fluorescence studies indicated more rapid fibril formation and less solvent accessibility of tryptophan (W26) in D69K apoC-II fibrils than in wild-type (WT) fibrils. X-ray diffraction data of aligned D69K apoC-II fibrils yielded a typical cross-β structure with increased β sheet spacing compared to that of WT fibrils. Hydrogen/deuterium (H/D) exchange patterns were similar for D69K apoC-II fibrils compared to WT fibrils, albeit with an overall reduction in the level of slow H/D exchange, particularly around residues 29-32. Molecular dynamics simulations indicated reduced β strand content for a model D69K apoC-II tetramer compared to the WT tetramer and confirmed an expansion of the cross-β spacing that contributed to the formation of a stable charge pair between K69 and E27. The results highlight the importance of charge-pair interactions within the apoC-II fibril core, which together with numerous salt bridges in the flexible connecting loop play a major role in the ability of lipid-free apoC-II to form stable cross-β fibrils.
authors.affiliation: †Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Yu
authors.initials: Y
authors.lastname: Mao
authors.affiliation: †Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Courtney O
authors.initials: CO
authors.lastname: Zlatic
authors.affiliation: †Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Michael D W
authors.initials: MD
authors.lastname: Griffin
authors.affiliation: †Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Geoffrey J
authors.initials: GJ
authors.lastname: Howlett
authors.affiliation: ‡Health Innovations Research Institute, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia.
authors.forename: Nevena
authors.initials: N
authors.lastname: Todorova
authors.affiliation: ‡Health Innovations Research Institute, RMIT University, GPO Box 2476, Melbourne, Victoria 3001, Australia.
authors.forename: Irene
authors.initials: I
authors.lastname: Yarovsky
authors.affiliation: †Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Gooley
mesh_terms: D000682:Amyloid / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053304:Apolipoprotein C-II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D041961:Deuterium Exchange Measurement; D006801:Humans; D056004:Molecular Dynamics Simulation; D020125:Mutation, Missense; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D013050:Spectrometry, Fluorescence
chemical_list: D000682:Amyloid; D053304:Apolipoprotein C-II