Essential subunit of the gamma-secretase complex, an endoprotease complex that catalyzes the intramembrane cleavage of integral membrane proteins such as Notch receptors and APP (beta- amyloid precursor protein). It probably represents a stabilizing cofactor required for the assembly of the gamma-secretase complex. Component of the gamma-secretase complex, a complex composed of a presenilin homodimer (PSEN1 or PSEN2), nicastrin (NCSTN), APH1 (APH1A or APH1B) and PEN2. Such minimal complex is sufficient for secretase activity, although other components may exist. Binds to proteolytic processed C-terminal fragments C83 and C99 of the amyloid precursor protein (APP). Constitutively expressed in neural cells. Widely expressed. Belongs to the nicastrin family. 2 isoforms of the human protein are produced by alternative splicing. Note: This description may include information from UniProtKB.