Required for the control of apoptosis during postnatal growth. Essential for proteolytic processing of an antiapoptotic form of opa1 which prevents the release of mitochondrial cytochrome c in response to intrinsic apoptotic signals (By similarity). Cleaves type-1 transmembrane domains using a catalytic dyad composed of serine and histidine that are contributed by different transmembrane domains. Interacts with psen1 and psen2. Binds opa1 (By similarity). Belongs to the peptidase S54 family.