SPAG17 (sperm associated antigen 17), also known as PF6, is a 2,223 amino acid cytoplamic protein that colocalizes with SPAG6 to microtubles. Highly expressed in testis and in organs that contain cilia-bearing cells including brain, oviduct, lung, and uterus, SPAG17 may be important for the structural integrity of the central apparatus of the sperm axoneme. SPAG17 contains two LRR (leucine-rich) repeats and may also participate in flagellar motility and male fertility.