Identification of Sperm-specific Proteins That Interact with A-kinase Anchoring Proteins in a Manner Similar to the Type II Regulatory Subunit of PKA

Abstract

The cAMP-dependent protein kinase (PKA) is targeted to specific subcellular compartments through its interaction with A-kinase anchoring proteins (AKAPs). AKAPs contain an amphipathic helix domain that binds to the type II regulatory subunit of PKA (RII). Synthetic peptides containing this amphipathic helix domain bind to RII with high affinity and competitively inhibit the 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, inhibition of the PKA catalytic activity does not mimic these peptides, suggesting that the peptides are disrupting the interaction of AKAP(s) with proteins other than PKA. Using the yeast two-hybrid system, we have now identified two sperm-specific human proteins that interact with the amphipathic helix region of AKAP110. These proteins, ropporin (a protein previously shown to interact with the Rho signaling pathway) and AKAPassociated sperm protein, 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 dimerization and AKAP binding. Mutation of conserved residues in ropporin or RII prevents binding to AKAP110. These data suggest that sperm contains several proteins that bind to AKAPs in a manner similar to RII and imply that AKAPs may have additional and perhaps unique functions in spermatozoa.

A Proteomic Analysis of Human Cilia

“…For some of these, the available information about these proteins suggests that they are axonemal proteins. For example, several sperm-or testisspecific proteins were identified, including an AKAP-associated sperm protein (30), SPAG 6, and Sp17. SPAG6 demonstrates 85% similarity to the Chlamydomonas protein pf16, which localizes to the flagellar central pair microtubules (31), whereas Sp17 has been localized to both the acrosomal region and throughout the sperm tail.…”

Moving to the beat: a review of mammalian sperm motility regulation

“…In addition to its structural support role, the FS may play a more direct role in the regulation of flagellar motility because a growing number of proteins involved in motility signalling pathways and metabolism have been localised to the FS (Carrera et al 1994;Bradley et al 1996;Westhoff and Kamp 1997;Bunch et al 1998;Miki and Eddy 1998;Mori et al 1998;Travis et al 1998;Turner et al 1998Turner et al , 1999Nakamura et al 1999;Fujita et al 2000;Carr et al 2001). It has also been suggested that at least one FS protein may act to protect sperm from oxidative stress, which could interfere with sperm motility or cause DNA damage (Fulcher et al 1995).…”

“…This finding suggests that, like other members of the AKAP family, AKAP4 is responsible for tethering several different proteins to a specific subcellular region. In this regard, other proteins have been implicated as being compartmentalised to the flagellum, and specifically to the FS, via interactions with anchoring proteins (Carr et al 2001;Brown et al 2003).…”

“…Heterotrimeric and small G-protein-mediated pathways, as well as pH changes, have also been implicated as playing roles in sperm motility, although these mechanisms are less well characterised in mature sperm (Hinsch et al 1993;Yanagimachi 1994;Nakamura et al 1999;Fujita et al 2000;Carr et al 2001;Wang et al 2003).…”

Oral phosphodiesterase-5 inhibitors and sperm functions

“…Normal mammalian sperm motility seems to be governed predominantly by the cAMP/PKA pathway and calcium signaling pathway, whereas mechanisms involving heterotrimeric and small G-proteins have also been entailed the regulation of sperm motility. 50 It should be emphasized that cAMP may also act through PKA-independent pathways. Burton et al 51 speculated that cAMP may activate a cyclic-nucleotide-gated ion channel in spermatozoa and/or cAMP-mediated guanine nucleotide exchange factors in testes, providing these ways as alternative pathways for the PKAmediated regulation of flagellar motility.…”