Component of the signal peptidase complex (SPC) which catalyzes the cleavage of N-terminal signal sequences from nascent proteins as they are translocated into the lumen of the endoplasmic reticulum (PubMed:3511473). Dispensable for SPC enzymatic activity (By similarity). Component of the signal peptidase complex paralog A (SPC-A) composed of a catalytic subunit SEC11A and three accessory subunits SPCS1, SPCS2 and SPCS3 (PubMed:3511473). Component of the signal peptidase complex paralog C (SPC-C) composed of a catalytic subunit SEC11C and three accessory subunits SPCS1, SPCS2 and SPCS3 (PubMed:3511473). Within the complex, interacts with SPCS2 and SPCS3 (By similarity). The complex induces a local thinning of the ER membrane which is used to measure the length of the signal peptide (SP) h-region of protein substrates (By similarity). This ensures the selectivity of the complex towards h-regions shorter than 18-20 amino acids (By similarity). Expressed in the pancreas (at protein level). May be phosphorylated. Belongs to the SPCS1 family.