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: Yu Mao, Courtney O Zlatic, Michael D W Griffin, Geoffrey J Howlett, Nevena Todorova, Irene Yarovsky, Paul R Gooley
• Journal: Biochemistry (Biochemistry) Vol. 54 Issue 31 Pg. 4805-14 (Aug 11 2015) ISSN: 1520-4995 [Electronic] United States
• PMID: 26196342 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Amyloid
• Apolipoprotein C-II

Topics

• Amyloid (chemistry, genetics, metabolism)
• Apolipoprotein C-II (chemistry, genetics, metabolism)
• Deuterium Exchange Measurement
• Humans
• Molecular Dynamics Simulation
• Mutation, Missense
• Protein Structure, Quaternary
• Protein Structure, Secondary
• Spectrometry, Fluorescence