This family consists of several eukaryotic Aph-1 proteins.Gamma-secretase catalyses the intramembrane proteolysis of Notch, beta-amyloid precursor protein, and other substrates as part of a new signaling paradigm and as a key step in the pathogenesis of Alzheimer's disease. It is thought that the presenilin heterodimer comprises the catalytic site and that a highly glycosylated form of nicastrin associates with it. Aph-1 and Pen-2, two membrane proteins genetically linked to gamma-secretase, associate directly with presenilin and nicastrin in the active protease complex. Co-expression of all four proteins leads to marked increases in presenilin heterodimers, full glycosylation of nicastrin, and enhanced gamma-secretase activity [1]. APH-1 proteins have a similar but different set of motifs as compared to other families. Their four motifs are: QExxR, Fxxxx, Hxxxs and Hxxxs respectively. Given the inferred homology between APH-1 and other membrane proteases such as type II CAAX proteases and PrsW proteases, it is speculated that APH-1 may possess protease activity [3].

1: {gamma}-Secretase is a membrane protein complex comprised of presenilin, nicastrin, aph-1, and pen-2. Kimberly WT, LaVoie MJ, Ostaszewski BL, Ye W, Wolfe MS, Selkoe DJ; Proc Natl Acad Sci U S A 2003;100:6382-6387. PMID:12740439

2: Different cofactor activities in {gamma}-secretase assembly: evidence for a nicastrin-Aph-1 subcomplex. Hu Y, Fortini ME; J Cell Biol 2003;161:685-690. PMID:12771124

3: Expansion of type II CAAX proteases reveals evolutionary origin of gamma-secretase subunit APH-1. Pei J, Mitchell DA, Dixon JE, Grishin NV; J Mol Biol. 2011;410:18-26. PMID:21570408