Lysine 624 of the Amyloid Precursor Protein (APP) Is a Critical Determinant of Amyloid β Peptide Length

• Published in: The Journal of biological chemistry 2011-11, Vol.286 (46), p.39804-39812
• Main Authors: Kukar, Thomas L., Ladd, Thomas B., Robertson, Paul, Pintchovski, Sean A., Moore, Brenda, Bann, Maralyssa A., Ren, Zhao, Jansen-West, Karen, Malphrus, Kim, Eggert, Simone, Maruyama, Hiroko, Cottrell, Barbara A., Das, Pritam, Basi, Guriqbal S., Koo, Edward H., Golde, Todd E.
• Format: Article
• Language: English
• Subjects: Alzheimer's Disease; Amyloid Precursor Protein; Aspartic Protease; Cell Biology; Intramembrane Proteolysis; Membrane Proteins; Neurodegenerative Diseases; Presenilin; Protease; Secretases
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M111.274696

γ-Secretase is a multiprotein intramembrane cleaving aspartyl protease (I-CLiP) that catalyzes the final cleavage of the amyloid β precursor protein (APP) to release the amyloid β peptide (Aβ). Aβ is the primary component of senile plaques in Alzheimer's disease (AD), and its mechanism of production has been studied intensely. γ-Secretase executes multiple cleavages within the transmembrane domain of APP, with cleavages producing Aβ and the APP intracellular domain (AICD), referred to as γ and ϵ, respectively. The heterogeneous nature of the γ cleavage that produces various Aβ peptides is highly relevant to AD, as increased production of Aβ 1–42 is genetically and biochemically linked to the development of AD. We have identified an amino acid in the juxtamembrane region of APP, lysine 624, on the basis of APP695 numbering (position 28 relative to Aβ) that plays a critical role in determining the final length of Aβ peptides released by γ-secretase. Mutation of this lysine to alanine (K28A) shifts the primary site of γ-secretase cleavage from 1–40 to 1–33 without significant changes to ϵ cleavage. These results further support a model where ϵ cleavage occurs first, followed by sequential proteolysis of the remaining transmembrane fragment, but extend these observations by demonstrating that charged residues at the luminal boundary of the APP transmembrane domain limit processivity of γ-secretase. Background: γ-Secretase modulators (GSMs) bind APP near lysine 624. Results: Mutation of lysine 624 shifts cleavage toward smaller Aβ with no effect on ϵ cleavage. Conclusion: The amino acid at 624 in substrates affects the final γ-secretase cut. Significance: γ-Secretase cleavage likely begins at ϵ and proceeds up the transmembrane until Aβ is released, and GSMs may modulate this process through lysine 624.