Calcium-binding protein that interacts with newly synthesized monoglucosylated glycoproteins in the endoplasmic reticulum. It may act in assisting protein assembly and/or in the retention within the ER of unassembled protein subunits. It seems to play a major role in the quality control apparatus of the ER by the retention of incorrectly folded proteins. Associated with partial T-cell antigen receptor complexes that escape the ER of immature thymocytes, it may function as a signaling complex regulating thymocyte maturation. Additionally it may play a role in receptor-mediated endocytosis at the synapse. Interacts with MAPK3/ERK1 (By similarity). Interacts with KCNH2 (By similarity). Associates with ribosomes (By similarity). The palmitoylated form interacts with the ribosome-translocon complex component SSR1, promoting efficient folding of glycoproteins (By similarity). Interacts with SERPINA2P/SERPINA2 and with the S and Z variants of SERPINA1 (By similarity). Interacts with SGIP1; involved in negative regulation of endocytosis (PubMed:21747946). Interacts with PPIB (By similarity). Interacts with SMIM22 (By similarity). Interacts with TMX2 (By similarity). Interacts with TMEM35A/NACHO (PubMed:32783947). Interacts with CHRNA7 (By similarity). The palmitoylated form preferentially localizes to the perinuclear rough ER (By similarity). When bound to CD3 epsilon chains, calnexin's ER retention signal can be masked, permitting it to escape ER retention. Phosphorylated at Ser-563 by MAPK3/ERK1. phosphorylation by MAPK3/ERK1 increases its association with ribosomes (By similarity). Palmitoylation by DHHC6 leads to the preferential localization to the perinuclear rough ER. It mediates the association of calnexin with the ribosome-translocon complex (RTC) which is required for efficient folding of glycosylated proteins (By similarity). Ubiquitinated, leading to proteasomal degradation. Probably ubiquitinated by ZNRF4. Belongs to the calreticulin family.