Calmegin (CLGN) is a member of the calreticulin family. Calmegin is a testis-specific endoplasmic reticulum chaperone protein. The functions during spermatogenesis as a chaperone for a range of client proteins that is important for sperm adhesion onto the egg zona pellucida and for subsequent penetration of the zona pellucida. It is required for normal male fertility, normal sperm migration from the uterus into the oviduct. Calmegin binds calcium ions and interacts with PDILT. Calmegin may play a role in spermatogeneisis and infertility.