Identification of sperm-specific proteins that interact with A-kinase anchoring proteins in a manner similar to the type II regulatory subunit of PKA

The cAMP-dependent protein kinase (PKA) is targeted to specific subcellular compartments through its interaction with A-kinase anchoring proteins (AKA Ps), AKAPs contain an amphipathic helix domain that binds to the type II re gulatory subunit of PKA (RII), Synthetic peptides containing this amphipath ic helix domain bind to RII with high affinity and competitively inhibit th e binding of PKA with AKAPs, Addition of these anchoring inhibitor peptides to spermatozoa inhibits motility (Vijayaraghavan, S., Goueli, S. A., Davey , M. P., and Carr, D. W. (1997) J. Biol, Chem. 272, 4747-4752), However, in hibition of the PKA catalytic activity does not mimic these peptides, sugge sting that the peptides are disrupting the interaction of AKAP(s) with prot eins other than PKA. Using the yeast two-hybrid system, we have now identif ied two sperm-specific human proteins that interact with the amphipathic he lix region of AKAP110, These proteins, ropporin (a protein previously shown to interact with the Rho signaling pathway) and AKAP-associated sperm prot ein, are 39% identical to each other and share a strong sequence similarity with the conserved domain on the N terminus of RII that is involved in dim erization and AKAP binding. Mutation of conserved residues in ropporin or R II prevents binding to AKAP110. These data suggest that sperm contains seve ral proteins that bind to AKAPs in a manner similar to RII and imply that A KAPs may have additional and perhaps unique functions in spermatozoa.