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. Author manuscript; available in PMC: 2017 May 18.
Published in final edited form as: ACS Chem Biol. 2015 Jun 10;10(8):1925–1931. doi: 10.1021/acschembio.5b00321

Figure 1.

Figure 1

Structural and functional similarities/differences between SPP and γ-secretase. SPP and γ-secretase are similar in that they are both multipass transmembrane enzymes that share the YD/GXGD catalytic motif and cleave their respective substrates in the transmembrane region. SPP and PS, the catalytic subunit of γ-secretase, both transverse the membrane 9 times. The differences between the enzymes include their limited sequence homology, their inverse orientation in the membrane, and their specificity for either type 1 or type 2 substrates. Additionally, SPP functions without protein cofactors while PS requires at least 3 additional proteins (Aph1, Nct, and Pen2) for γ-secretase activity.