PT - JOURNAL ARTICLE AU - Chihiro Sato AU - Shizuka Takagi AU - Taisuke Tomita AU - Takeshi Iwatsubo TI - The C-Terminal PAL Motif and Transmembrane Domain 9 of Presenilin 1 Are Involved in the Formation of the Catalytic Pore of the γ-Secretase AID - 10.1523/JNEUROSCI.1163-08.2008 DP - 2008 Jun 11 TA - The Journal of Neuroscience PG - 6264--6271 VI - 28 IP - 24 4099 - http://www.jneurosci.org/content/28/24/6264.short 4100 - http://www.jneurosci.org/content/28/24/6264.full SO - J. Neurosci.2008 Jun 11; 28 AB - γ-Secretase is an unusual membrane-embedded protease, which cleaves the transmembrane domains (TMDs) of type I membrane proteins, including amyloid-β precursor protein and Notch receptor. We have previously shown the existence of a hydrophilic pore formed by TMD6 and TMD7 of presenilin 1 (PS1), the catalytic subunit of γ-secretase, within the membrane by the substituted cysteine accessibility method. Here we analyzed the structure of TMD8, TMD9, and the C terminus of PS1, which encompass the conserved PAL motif and the hydrophobic C-terminal tip, both being critical for the catalytic activity and the formation of the γ-secretase complex. We found that the amino acid residues around the PAL motif and the extracellular/luminal portion of TMD9 are highly water accessible and located in proximity to the catalytic pore. Furthermore, the region starting from the luminal end of TMD9 toward the C terminus forms an amphipathic α-helix-like structure that extends along the interface between the membrane and the extracellular milieu. Competition analysis using γ-secretase inhibitors revealed that the TMD9 is involved in the initial binding of substrates, as well as in the subsequent catalytic process as a subsite. Our results provide mechanistic insights into the role of TMD9 in the formation of the catalytic pore and the substrate entry, crucial to the unusual mode of intramembrane proteolysis by γ-secretase.