The function of Ensembl gene identifier ENSG00000109133 (TMEM33, transmembrane protein 33) is as follows. Acts as a regulator of the tubular endoplasmic reticulum (ER) network by modulating intracellular calcium homeostasis. Mechanistically, stimulates PKD2 calcium-dependent activity (By similarity). Suppresses the RTN3/4-induced formation of the ER tubules (PubMed:25612671). Positively regulates PERK-mediated and IRE1-mediated unfolded protein response signaling (PubMed:26268696). Plays an essential role in VEGF-mediated release of Ca(2+) from ER stores during angiogenesis (PubMed:30760708). Also plays a role in the modulation of innate immune signaling through the cGAS-STING pathway by interacting with RNF26 (PubMed:32614325). Participates in lipid metabolism by acting as a downstream effector of the pyruvate kinase/PKM. Forms a complex with RNF5 to facilitate polyubiquitination and subsequent degradation of SCAP on the ER membrane (PubMed:34487377). {ECO:0000250|UniProtKB:Q9CR67, ECO:0000269|PubMed:25612671, ECO:0000269|PubMed:26268696, ECO:0000269|PubMed:30760708, ECO:0000269|PubMed:32614325, ECO:0000269|PubMed:34487377}.