Conservation and function of a bovine sperm A-kinase anchor protein homologous to mouse AKAP82

Protein kinase A regulates sperm motility through the cAMP-dependent phosph orylation of proteins. One mechanism to direct the activity of the kinase i s to localize it near its protein substrates through the use of anchoring p roteins. A-Kinase anchoring proteins (AKAPs) act by binding the type It reg ulatory subunit of protein kinase A and tethering it to a cellular organell e or cytoskeletal element. We showed previously that mAKAP82, the major pro tein of the fibrous sheath of the mouse sperm flagellum, is an AKAP. The av ailable evidence indicates that protein kinase A is compartmentalized to th e fibrous sheath by binding mAKAP82. To characterize AKAP82 in bovine sperm , a testicular cDNA library was constructed and used to isolate a clone enc oding bAKAP82, the bovine homologue. Sequence analysis showed that the prim ary structure of bAKAP82 was highly conserved. In particular, the amino aci d sequence corresponding to the region of mAKAP82 responsible for binding t he regulatory subunit of protein kinase A was identical in the bull. Bovine AKAP82 was present in both epididymal and ejaculated sperm and was localiz ed to the entire principal piece of the flagellum, the region in which the fibrous sheath is located. Finally, bAKAP82 bound the regulatory subunit of protein kinase A. These data support the idea that bAKAP82 functions as an anchoring protein for the subcellular localization of protein kinase A in the flagellum.