Major structural component of sperm fibrous sheath. Plays a role in sperm motility. Interacts with PRKAR1A and PRKAR2A. Interacts with ENO4. Localizes to the principle piece of the sperm flagellum. Testis specific; only expressed in round spermatids. Post-meiotic phase of spermatogenesis. RI-alpha binding site, predicted to form an amphipathic helix, could participate in protein-protein interactions with a complementary surface on the R-subunit dimer. Belongs to the AKAP110 family.