Cholesterol twists the transmembrane Di-Gly region of amyloid-precursor protein

David Tzu-Wei Wang; Tiffany Y C Tang; Chun-Ting Kuo; Yun-Ting Yu; Eric H L Chen; Ming-Tao Lee; Ruei-Fong Tsai; Hung-Ying Chen; Yun-Wei Chiang; Rita P Y Chen

doi:10.1093/pnasnexus/pgad162

Cholesterol twists the transmembrane Di-Gly region of amyloid-precursor protein

PNAS Nexus. 2023 May 17;2(5):pgad162. doi: 10.1093/pnasnexus/pgad162. eCollection 2023 May.

Authors

David Tzu-Wei Wang^{1

2}, Tiffany Y C Tang¹, Chun-Ting Kuo^{1

2}, Yun-Ting Yu^{1

2}, Eric H L Chen¹, Ming-Tao Lee^{3

4}, Ruei-Fong Tsai⁵, Hung-Ying Chen⁵, Yun-Wei Chiang⁵, Rita P Y Chen^{1

2

6}

Affiliations

¹ Institute of Biological Chemistry, Academia Sinica, Taipei 11529, Taiwan.
² Institute of Biochemical Sciences, National Taiwan University, Taipei 10617, Taiwan.
³ Life Science Group, Scientific Research Division, National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan.
⁴ Department of Physics, National Central University, Zhongli 320317, Taiwan.
⁵ Department of Chemistry, National Tsing Hua University, Hsinchu 300044, Taiwan.
⁶ Neuroscience Program of Academia Sinica, Taipei 11529, Taiwan.

Abstract

Nearly 95% of Alzheimer's disease (AD) occurs sporadically without genetic linkage. Aging, hypertension, high cholesterol content, and diabetes are known nongenomic risk factors of AD. Aggregation of Aβ peptides is an initial event of AD pathogenesis. Aβ peptides are catabolic products of a type I membrane protein called amyloid precursor protein (APP). Aβ40 is the major product, whereas the 2-residue-longer version, Aβ42, induces amyloid plaque formation in the AD brain. Since cholesterol content is one risk factor for sporadic AD, we aimed to explore whether cholesterol in the membrane affects the structure of the APP transmembrane region, thereby modulating the γ-secretase cutting behavior. Here, we synthesized several peptides containing the APP transmembrane region (sequence 693-726, corresponding to the Aβ_22-55 sequence) with one or two Cys mutations for spin labeling. We performed three electron spin resonance experiments to examine the structural changes of the peptides in liposomes composed of dioleoyl phosphatidylcholine and different cholesterol content. Our results show that cholesterol increases membrane thickness by 10% and peptide length accordingly. We identified that the di-glycine region of Aβ_36-40 (sequence VGGVV) exhibits the most profound change in response to cholesterol compared with other segments, explaining how the presence of cholesterol affects the γ-secretase cutting site. This study provides spectroscopic evidence showing how cholesterol modulates the structure of the APP transmembrane region in a lipid bilayer.

Keywords: Alzheimer's disease; Aβ; amyloid precursor protein; cholesterol; electron spin resonance spectroscopy; lamellar X-ray diffraction; orientated circular dichroism spectroscopy; transmembrane helix.