Sigma-2 receptor implicated in the regulation of multiple cellular processes, including cholesterol biosynthesis and trafficking, membrane trafficking, autophagy, lipid membrane-associated protein trafficking, and stabilization of receptors at the cell surface, thereby contributing to the maintenance of cellular homeostasis(PubMed:19583955, PubMed:23922215, PubMed:25620095, PubMed:27378690, PubMed:28559337, PubMed:30443021, PubMed:34233061, PubMed:34799735, PubMed:35970844, PubMed:25566323). Forms a ternary complex with PGRMC1 and LDLR at the plasma membrane, promoting LDLR- mediated internalization of LDL cholesterol (PubMed:30443021). Reduces the availability of the lysosomal sterol transporter NPC1, likely through direct interaction, thereby regulating lipid transport, including cholesterol and LBPA, outside of late endosome/lysosome (PubMed:19583955, PubMed:27378690). Binds the regio- and stereoselective oxysterol 20(S)-hydroxycholesterol (20(S)-OHC). Ligand binding enhances association with NPC1 and modulates TMEM97-containing protein complexes involving PGRMC1 and TSPO, consistent with a role in cholesterol homeostasis (PubMed:34799735, PubMed:37047353). Also able to bind cholesterol (By similarity). Interacts with the salivary peptide histatin 1 (Hst 1/HTN1) at the ER membrane, which is critical for increasing mitochondria-ER contacts and stimulating Hst 1 wound healing properties (PubMed:34233061, PubMed:35970844). May alter the activity of some cytochrome P450 proteins (PubMed:22292588). Although sharing homology with sterol isomerases through the EXPERA domain, lacks sterol isomerase activity; instead, may function as a sterol or oxysterol sensor (PubMed:34880501, PubMed:25566323). Acts as an ER quality control factor by promoting proteolytic degradation of nonproductive and extramitochondrial precursor proteins in the ER membrane, thereby removing them from the ER surface (By similarity). {ECO:0000250|UniProtKB:Q3MHW7, ECO:0000269|PubMed:19583955, ECO:0000269|PubMed:25566323, ECO:0000269|PubMed:27378690, ECO:0000269|PubMed:28559337, ECO:0000269|PubMed:30443021, ECO:0000269|PubMed:34233061, ECO:0000269|PubMed:34799735, ECO:0000269|PubMed:34880501, ECO:0000269|PubMed:35970844, ECO:0000269|PubMed:37047353, ECO:0000303|PubMed:22292588, ECO:0000303|PubMed:23922215, ECO:0000303|PubMed:25620095}. This is the function of TMEM97 (transmembrane protein 97, ENSG00000109084).