The first proline of PALP motif at the C terminus of presenilins is obligatory for stabilization, complex formation, and gamma-secretase activities of presenilins

Mutations in presenilin (PS) genes cause early-onset familial Alzheimer's d isease by increasing production of the amyloidogenic form of amyloid beta p eptides ending at residue 42 (A beta 42). PS is an evolutionarily conserved multipass transmembrane protein, and all known PS proteins contain a proli ne-alanine-leucine-proline (PALP) motif starting at proline (P) 414 (amino acid numbering based on human PS2) at the C terminus. Furthermore, missense mutations that replace the first proline of PALP with leucine (P414L) lead to a loss-of-function of PS in Drosophila melanogaster and Caenorhabditis elegans. To elucidate the roles of the PALP motif in PS structure and funct ion, we analyzed neuro2a as well as PS1/2 null fibroblast cell lines transf ected with human PS harboring mutations at the PALP motif. P414L mutation i n PS2 (and its equivalent in PS1) abrogated stabilization, high molecular w eight complex formation, and entry to Golgi/trans-Golgi network of PS prote ins, resulting in failure of A beta 42 overproduction on familial Alzheimer 's disease mutant basis as well as of site-3 cleavage of Notch. These data suggest that the first proline of the PALP motif plays a crucial role in th e stabilization and formation of the high molecular weight complex of PS, t he latter being the active form with intramembrane proteolytic activities.