May function as a regulator of both motility- and head-associated functions such as capacitation and the acrosome reaction. Interacts with ROPN1 AND ROPN1L. Interacts with QRICH2 (PubMed:30683861). Ribs of the fibrous sheath in the principal piece of the sperm tail. Dorsal margin of the acrosomal segment. Testis specific; only expressed in spermatids. RII-binding site, predicted to form an amphipathic helix, could participate in protein-protein interactions with a complementary surface on the R-subunit dimer. Phosphorylated on tyrosine residues. Belongs to the AKAP110 family.