Involved in regulated intramembrane proteolysis and the subsequent release of functional polypeptides from their membrane anchors. Known substrate: EFNB3. Cleaves type-1 transmembrane domains using a catalytic dyad composed of serine and histidine that are contributed by different transmembrane domains. Proteolytic processing of the proenzyme produces a N-terminal fragment (NTF) and a C-terminal fragment (CTF). The processing is required for activation of the protease. May be due to an intron retention. Belongs to the peptidase S54 family. Truncated N-terminus. Truncated N-terminus.