Metalloprotease that catalyzes the second step (site-2 cleavage) in the proteolytic activation of various factors, after site-1 cleavage. Part of a regulated intramembrane proteolysis (RIP) cascade. After ER stress, cleaves BZIP17 and BZIP28 proteins which functions as stress sensors and transducers in ER stress signaling pathway. The N-terminal bZIP component is translocated to the nucleus, where it activates the expression and production of ER chaperones, as well as proteins involved in brassinosteroid (BR) signaling, which is required for stress acclimation and growth. A number of isoforms are produced. According to EST sequences. Expressed in the vasculature of roots, cotyledons and leaves. Short root and increased root branching. Mutant plants have increased sensitivity to salt-induced osmotic stress and tunicamycin. Belongs to the peptidase M50A family.