Calnexin is a calcium-binding protein that interacts with newly synthesized glycoproteins in the endoplasmic reticulum. It may act to assist protein assembly and/or play a role in the retention of unassembled protein subunits within the ER. It seems to play a major role in the quality control apparatus of the ER by the retention of incorrectly folded proteins. Calnexin is also ssociated with partial T-cell antigen receptor complexes that escape the ER of immature thymocytes, and may function as a signaling complex regulating thymocyte maturation. Additionally, Calnexin may play a role in receptor-mediated endocytosis at the synapse.