Calmegin is a testis-specific endoplasmic reticulum chaperone protein. CLGN may play a role in spermatogeneisis and infertility. Functions during spermatogenesis as a chaperone for a range of client proteins that are important for sperm adhesion onto the egg zona pellucida and for subsequent penetration of the zona pellucida. Required for normal sperm migration from the uterus into the oviduct. Required for normal male fertility. Binds calcium ions (By similarity).