Ropporin 1B (ROPN1B)

AKAP 3, also known as AKAP 110, FSP95, PRKA3 and SOB1, binds both PKA and PDE4A and functions as a scaffolding protein in spermatozoa to regulate local cAMP concentrations and modulate sperm functions. Expression of AKAP 3 in normal tissues is restricted to the testis, where bicarbonate stimulates tyrosine phosphorylation of AKAP 3, thereby increasing its recruitment of PKA. AKAP 3 serves as an anchoring protein for ROPN1, also designated Ropporin. ROPN1 expression is limited to testis and fetal liver in normal tissues, but can also be detected in multiple myeloma, chronic lymphocytic leukemia and acute myeloid leukemia tumor cells. ROPN1 forms a complex with rhophilin in sperm flagella to mediate its function. ROPN1B (ropporin-1B) is a 212 amino acid protein that interacts with ROPN1 and AKAP 3. ROPN1B is localized to the sperm tail, specifically to the inner surface of the fibrous sheath.