Butyrophilin Subfamily 3, Member A1 (BTN3A1)

The butyrophilins (BTN) belong to the Ig superfamily, and are encoded in a cluster of seven genes in the extended MHC class I region on chromosome 6 . BTN1, BTN2, and BTN3 subfamilies share 50% amino acid identity. The extracellular domains of the three members within each subfamily are more closely related and share 88% (BTN2A1, -A2 and -A3) and 95% (BTN3A1, -A2 and -A3) identity, respectively.BTN1, the prototype of the family, is a major component of the milk fat globule membrane and is regulated by lactogenic hormones. BTN1 has a crucial function in the secretion of lipids into milk. Collectively, BTN2 and BTN3 are cell surface transmembrane glycoproteins, transcripts of which are ubiquitously expressed at a low to intermediate level.