Hydrogen/Deuterium Exchange and Molecular Dynamics Analysis of Amyloid Fibrils Formed by a D69K Charge-Pair Mutant of Human Apolipoprotein C-II

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• 作者：Yu Mao ; Courtney O. Zlatic ; Michael D. W. Griffin ; Geoffrey J. Howlett ; Nevena Todorova ; Irene Yarovsky ; Paul R. Gooley
• 刊名：Biochemistry
• 出版年：2015
• 出版时间：August 11, 2015
• 年：2015
• 卷：54
• 期：31
• 页码：4805-4814
• 全文大小：638K
• ISSN：1520-4995

文摘

Plasma apolipoproteins form amphipathic 伪 helices in lipid environments but in the lipid-free state show a high propensity to form 尾 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 伪 helices or cross-尾 sheet structures, we examined fibrils formed by human apolipoprotein C-II (apoC-II). A structural model for apoC-II fibrils shows a cross-尾 core with parallel 尾 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-尾 structure with increased 尾 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鈥?2. Molecular dynamics simulations indicated reduced 尾 strand content for a model D69K apoC-II tetramer compared to the WT tetramer and confirmed an expansion of the cross-尾 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-尾 fibrils.