ELSPBP1 (epididymal sperm-binding protein 1), also known as epididymal secretory protein 12 (E12), HE12 or EDDM12, is a 223 amino acid member of the seminal plasma protein family. ELSPBP1 is a secreted protein that is detected in cauda epididymidal fluid and on sperm membrane. ELSPBP1 has phosphorylcholine-binding activity and has been shown to bind to spermatozoa upon ejaculation and is thought to play a role in sperm capacitation. N-glycosylated, ELSPBP1 contains four fibronectin type-II domains. The gene that encodes ELSPBP1 maps to human chromosome 19, which consists of over 63 million bases, houses approximately 1,400 genes and is recognized for having the greatest gene density of the human chromosomes.