A histidine-mediated supramolecular mechanism links temperature and pH activation of the sperm channel CatSper.

Abstract

The cation channel of sperm, CatSper, is a sperm-specific calcium channel essential for male fertility across metazoans. CatSper is activated by intracellular alkalinization, membrane depolarization, and elevated temperature, which together ensure maximal current generation. However, the structural mechanisms by which these physiological stimuli jointly regulate channel activation remain poorly understood, in part because CatSper is an unusually complex ~15-subunit assembly organized in zigzag supramolecular arrays along the sperm flagellum. Here, we combine comparative genomics across 47 species with AlphaFold3-based modeling and evolutionary sequence-structure analyses to investigate a mechanism underlying temperature and pH sensitivity of CatSper. Phylogenetic analysis shows that N-terminal length and histidine enrichment of the pore-forming subunit CatSper1 strongly correlate with species-specific fertilization temperatures, suggesting evolutionary adaptation of temperature and pH sensitivity. Structural modeling further revealed conserved surface-exposed histidine clusters that form predicted contact interfaces between adjacent CatSper assemblies, with this contact interface positioned near the dominant voltage-sensing module. Functional validation using electrophysiology and calcium imaging in mouse sperm shows that capacitation-associated partial removal of the CatSper1 N-terminus selectively impairs temperature-dependent activation. Together, these findings support a model in which temperature-dependent histidine deprotonation functionally couples neighboring CatSper complexes within the supramolecular assembly, thereby promoting synchronized channel activation.