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:34388369). Enhances the enzymatic activity of SPC and facilitates the interactions between different components of the translocation site (By similarity). {ECO:0000250|UniProtKB:Q04969, ECO:0000269|PubMed:34388369}. This is the function of ENSG00000118363 (SPCS2, signal peptidase complex subunit 2).