Competition Between Homodimerization and Cholesterol Binding to the C99 Domain of the Amyloid Precursor Protein

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• 作者：Yuanli Song ; Eric J. Hustedt ; Suzanne Brandon ; Charles R. Sanders
• 刊名：Biochemistry
• 出版年：2013
• 出版时间：July 30, 2013
• 年：2013
• 卷：52
• 期：30
• 页码：5051-5064
• 全文大小：574K
• 年卷期：v.52,no.30(July 30, 2013)
• ISSN：1520-4995

文摘

The 99-residue transmembrane C-terminal domain (C99, also known as 尾-CTF) of the amyloid precursor protein (APP) is the product of the 尾-secretase cleavage of the full-length APP and is the substrate for 纬-secretase cleavage. The latter cleavage releases the amyloid-尾 polypeptides that are closely associated with Alzheimer鈥檚 disease. C99 is thought to form homodimers; however, the free energy in favor of dimerization has not previously been quantitated. It was also recently documented that cholesterol forms a 1:1 complex with monomeric C99 in bicelles. Here, the affinities for both homodimerization and cholesterol binding to C99 were measured in bilayered lipid vesicles using both electron paramagnetic resonance (EPR) and F枚rster resonance energy transfer (FRET) methods. Homodimerization and cholesterol binding were seen to be competitive processes that center on the transmembrane G₇₀₀XXXG₇₀₄XXXG₇₀₈ glycine-zipper motif and adjacent Gly709. On one hand, the observed K_d for cholesterol binding (K_d = 2.7 卤 0.3 mol %) is on the low end of the physiological cholesterol concentration range in mammalian cell membranes. On the other hand, the observed K_d for homodimerization (K_d = 0.47 卤 0.15 mol %) likely exceeds the physiological concentration range for C99. These results suggest that the 1:1 cholesterol/C99 complex will be more highly populated than C99 homodimers under most physiological conditions. These observations are of relevance for understanding the 纬-secretase cleavage of C99.