American Society for Biochemistry and Molecular Biology
Journal of Biological Chemistry vol:286 pages:22339-22347
Missense mutations in presenilin 1 (PS1) and presenilin 2 (PS2) proteins are a major cause of familial Alzheimers disease (FAD). Presenilin 1 and PS2 are proteins with 9 transmembrane (TM) domains which function as catalytic subunits of the g-secretase complex responsible for the cleavage of the amyloid precursor protein (APP) and other type I transmembrane proteins. The water-filled cavity within presenilin is necessary to mediate the intramembrane proteolysis reaction. Consistent with this idea, cysteine-scanning mutagenesis (SCAM) and NMR studies revealed a number of water-accessible residues within TM7 and TM9 of mouse PS1 (mPS1). In addition to g-secretase function, presenilins also demonstrate a low conductance, endoplasmic reticulum (ER) calcium (Ca2+) leak function and many FAD presenilin mutations impair this function. In order to map the potential Ca2+ conductance pore in PS1, we systematically evaluated ER Ca2+ leak activity supported by a series of cysteine point mutants in TM6, TM7 and TM9 of mPS1. The results indicated that TM7 and TM9, but not TM6, could play an important role in forming the conductance pore of PS1. These results are consistent with previous SCAM and NMR analysis of PS1 and provide further support to our hypothesis that the hydrophilic catalytic cavity of presenilins may also constitute a Ca2+ conductance pore.