Intracellular domain of CATSPER1 could serve as a cytoplasmic platform for redox processes in mammalian sperm

Mammalian sperm acquire fertilizing ability in the female reproductive tract and develop hyperactivated motility, which is indispensable for male fertility. Hyperactivated motility is initiated by Ca2+ influx via the sperm-specific ion channel, CatSper. CATSPER1, a CatSper pore subunit, possesses a long N-terminal intracellular domain and its degradation correlates with unsuccessful sperm migration in the female tract. However, the cellular function and molecular significance of the CATSPER1 N-terminal domain are not well understood. Here, we identify the interactome of the CATSPER1 N-terminal domain and propose a function for the intracellular domain in mammalian sperm.

To identify CATSPER1 N-terminus interactome, we produced recombinant CATSPER1-N-terminus in bacterial system. The purified protein was incubated with testicular lysates and eluted together with testicular interacting proteins. The elutes were subjected to proteomic analysis and CATSPER1-N-terminus interactome was profiled. Identified proteins were further analyzed by functional annotation.

We purified the partial CATSPER1 N-terminal domain and identified 57 testicular proteins as domain interactomes using mass spectrometry analysis. Functional annotation analysis revealed that 106 gene ontologies were significantly enriched, 16 of which were related to redox processes. We found that antioxidant enzymes, such as PARK7 and PRDX2, 4, and 6, were included in the enriched redox-related gene ontologies.

These results suggest that the CATSPER1 N-terminus could function in defending against oxidative stress to support the successful migration of mammalian sperm to fertilizing sites in the female reproductive tract.