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Impact of bilayer lipid composition on the structure and topology of the transmembrane amyloid precursor C99 protein.

ABSTRACT: C99 (also known as ?-CTF) is the 99 residue transmembrane C-terminal domain (residues 672-770) of the amyloid precursor protein and is the immediate precursor of the amyloid-? (A?) polypeptides. To test the dependence of the C99 structure on the composition of the host model membranes, NMR studies of C99 were conducted both in anionic lyso-myristoylphosphatidylglycerol (LMPG) micelles and in a series of five zwitterionic bicelle compositions involving phosphatidylcholine and sphingomyelin in which the acyl chain lengths of these lipid components varied from 14 to 24 carbons. Some of these mixtures are reported for the first time in this work and should be of broad utility in membrane protein research. The site-specific backbone (15)N and (1)H chemical shifts for C99 in LMPG and in all five bicelle mixtures were seen to be remarkably similar, indicating little dependence of the backbone structure of C99 on the composition of the host model membrane. However, the length of the transmembrane span was seen to vary in a manner that alters the positioning of the ?-secretase cleavage sites with respect to the center of the bilayer. This observation may contribute to the known dependency of the A?42-to-A?40 production ratio on both membrane thickness and the length of the C99 transmembrane domain.

SUBMITTER: Song Y

PROVIDER: S-EPMC3985881 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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Impact of bilayer lipid composition on the structure and topology of the transmembrane amyloid precursor C99 protein.

Song Yuanli Y Mittendorf Kathleen F KF Lu Zhenwei Z Sanders Charles R CR

Journal of the American Chemical Society 20140311 11

C99 (also known as β-CTF) is the 99 residue transmembrane C-terminal domain (residues 672-770) of the amyloid precursor protein and is the immediate precursor of the amyloid-β (Aβ) polypeptides. To test the dependence of the C99 structure on the composition of the host model membranes, NMR studies of C99 were conducted both in anionic lyso-myristoylphosphatidylglycerol (LMPG) micelles and in a series of five zwitterionic bicelle compositions involving phosphatidylcholine and sphingomyelin in whi ...[more]

PMID: 24564538

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Project description:Elevated levels of cellular cholesterol have been identified as one factor contributing to the onset of Alzheimer's disease (AD). Specific interaction between cholesterol and the amyloid precursor protein (APP), investigated via NMR experiments and computational studies, has been proposed to play a critical role in the processing of APP by secretases and the biogenesis of amyloid-β (Aβ) protein. We present all-atom molecular dynamics simulations of the 40-residue congener of the C-terminal domain of APP, C9916-55 (C99), in cholesterol-enriched DMPC lipid bilayers. We investigated the effect of cholesterol concentration on the conformational ensemble of wild-type C99 and C99-cholesterol associations at the low pH of endosomal environments, at which residues E22 and D23 are neutral. C99 was also characterized in liquid ordered domains for Dutch (E22Q) and Iowa (D23N) Familial AD mutants at low pH and for the wild-type sequence using protonation states characteristic of neutral pH. Our results reproduce the equilibrium constant of past NMR characterizations of the C99-cholesterol interaction but are not consistent with the C99-cholesterol binding hypothesis. We find that the lifetimes of both DMPC and cholesterol complexed with C99 display a power-law distribution of residence lifetimes. Longer-lived C99-DMPC and C99-cholesterol complexes are primarily stabilized by salt bridges and hydrogen bonds of lysine amines to phosphate and hydroxyl groups. Nevertheless, specific interfaces for C99-cholesterol association which are not present for DMPC can be identified. Changes to C99-cholesterol interfaces are found to depend on C99 tilt angle and orientation of the juxtamembrane domain of C99 containing residues E22 and D23. These observations support a more nuanced view of the C99-cholesterol interaction than has previously been suggested. We propose that cholesterol modulates the conformation and activity of C99 and other small transmembrane proteins indirectly through induction of the liquid ordered phase and directly through hydrogen bonding. This suggests a critical role for membrane heterogeneity introduced by cholesterol in modulating the structural ensemble of C99 and the production of Aβ.

Dataset Information

Impact of bilayer lipid composition on the structure and topology of the transmembrane amyloid precursor C99 protein.

Publications

Impact of bilayer lipid composition on the structure and topology of the transmembrane amyloid precursor C99 protein.

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