Tracing the GSAP-APP C-99 Interaction Site in the β-Amyloid Pathway Leading to Alzheimer's Disease

Gamma secretase activating protein (GSAP) present in β-amyloid pathway orchestrates the formation of β-amyloid plaques by γ-secretase activation and is an emerging therapeutic target for the treatment of Alzheimer's disease. It forms a ternary complex with γ-secretase and APP C-99. However, there are limited reports for the interaction of APP C-99 with GSAP. Here, we report the characterization of purified maltose binding protein (MBP) tagged human GSAP and its interaction with synthetic APP C-99 peptide fragments (⁷¹²IATVIVITLVMLKKQ⁷²⁷ (⁷¹²IQ⁷²⁷), ⁷¹⁹TLVMLKKKQYTSIHHGVVEVDAAVT⁷⁴³ (⁷¹⁹TT⁷⁴³) ⁷³⁴GVVEVDAAVTPEERHLSKMQQNGY⁷⁵⁷ (⁷³⁴GY⁷⁵⁷), and ⁷⁴⁶ERHLSKMQQNGYENPTYKFFEQMQN⁷⁷⁰ (⁷⁴⁶EN⁷⁷⁰)). The results emphasize the selective interaction of peptide (⁷¹⁹TT⁷⁴³) with MBP-GSAP with a dissociation constant of 0.136 μM. Further, computational modeling of the GSAP-⁷¹⁹TT⁷⁴³ complex finds an optimal bound pose of ⁷¹⁹TT⁷⁴³ within an extended groove on the surface of GSAP. The preliminary results highlight the interaction between the two major proteins in the plausible ternary complex: APP C-99-GSAP-γ-secretase. It paves a futuristic path to investigate the GSAP-APP C-99 binding in detail and accentuates the role of GSAP in the β-amyloid pathway.