Sperm acrosome membrane-associated protein 6 (SPACA6)

Sperm acrosome membrane-associated protein 6 (SPACA6) is a conserved, testis-specific type I transmembrane glycoprotein, essential for gamete fusion during mammalian fertilization. The protein is localized initially to the acrosomal cap of sperm and relocalizes to the equatorial segment during the acrosome reaction—a location coinciding with the site of membrane fusion with the oocyte. Structurally, SPACA6 contains a four-helix bundle and an immunoglobulin-like (Ig-like) β-sandwich domain, and shares key motifs with IZUMO1, defining the newly classified IST superfamily of fertilization-associated proteins. Gene knockout studies in mice and zebrafish show that SPACA6 is indispensable for fertilization; sperm lacking SPACA6 cannot fuse with oocytes, resulting in complete male infertility. There is no evidence for expression or functional relevance outside the reproductive tract, nor for interaction with approved drugs. Recent structural characterization and evolutionary analysis mark SPACA6 as a pivotal molecular player exclusive to sperm-egg fusion biology.

Other names

SPACA6Sperm acrosome associated 6Sperm acrosome membrane-associated protein 6SPACA6PUNQ2487/PRO5774LET7EHBACHELOR-like proteinLINC00085NCRNA00085

Not applicable; however, experimental inhibition by antibodies prevents sperm–egg fusion in vitro indicating that blockade of SPACA6 could impair fertilization