EFCAB9 is a pH-Dependent Ca²⁺Sensor that Regulates CatSper Channel Activity and Sperm Motility

Abstract

16Varying pH of luminal fluid along the female reproductive tract is a physiological cue that 17 modulates sperm motility. CatSper is a sperm-specific, pH-sensitive calcium channel essential 18 for hyperactivated motility and male fertility. Multi-subunit CatSper channel complexes organize 19 linear Ca 2+ signaling nanodomains along the sperm tail. Here, we identify EF-hand calcium-20 binding domain-containing protein 9 (EFCAB9) as a dual function, cytoplasmic machine 21 modulating the channel activity and the domain organization of CatSper. Knockout mice studies 22 demonstrate that EFCAB9, in complex with the CatSper subunit, CATSPER, is essential for pH-23 dependent and Ca 2+ sensitive activation of the CatSper channel. In the absence of EFCAB9, 24 sperm motility and fertility is compromised and the linear arrangement of the Ca 2+ signaling 25 domains is disrupted. EFCAB9 interacts directly with CATSPER in a Ca 2+ dependent manner 26 and dissociates at elevated pH. These observations suggest that EFCAB9 is a long-sought, 27 intracellular, pH-dependent Ca 2+ sensor that triggers changes in sperm motility. 28 29 Keywords (up to 10 keywords) 30 Sperm motility, male fertility, Ca 2+ channel, CatSper, pH sensing, Ca 2+ sensor, Ca 2+ signal 31 transduction 32 33 Highlights 34  Efcab9 encodes an evolutionarily conserved, sperm-specific EF-hand domain protein 35  Efcab9-deficient mice have sperm motility defects and reduced male fertility 36  EFCAB9 is a pH-tuned Ca 2+ sensor for flagellar CatSper Ca 2+ channel 37  EFCAB9 is a dual function machine in gatekeeping and domain organization of CatSper 38 39 82super-resolution imaging levels. We find that EFCAB9 is a pH-dependent Ca 2+ sensor for the 83 CatSper channel. EFCAB9-CatSper forms a binary complex and interacts with the pore as a 84 gatekeeper, activating CatSper channel responding to capacitation-associated intracellular 85 changes. EFCAB9 interaction with CatSper requires its Ca 2+ binding to EF-hands, which are 86 responsive to pH changes in a physiologically relevant range. Loss of EFCAB9-CatSper largely 87 Hwang et al.,2018 3 eliminates the pH-dependent and Ca 2+ sensitive activation of CatSper and alters newly resolved 88 CatSper Ca 2+ signaling domains. In contrast to the recent addition of CatSper to mammals, the 89 EFCAB9 and other transmembrane CatSper subunits are evolutionarily conserved from 90 flagellated single cell eukaryotes. These findings provide insight into evolutionarily conserved 91 gating mechanisms for CatSper channels and reveal an adaptation for Ca 2+ signaling in flagella. 92 93 RESULTS 94 95 97 Sperm hyperactivated motility requires pH-dependent activation of the CatSper flagellar Ca 2+ 98 channel. The CatSper channel forms a multi-protein complex composed of at least nine subunits 99 (CatSper1-4, , , , , and ) (Chung et al., 2017). Here we examine a new member of the 100 complex and determine its functional significance. 101 102Our previous studies showed that other CatSper subunits were not detected in CatSper1-a...

Genes predisposing to syndromic and nonsyndromic infertility: a narrative review

“…5q35.1 Encodes sperm-specific EF-band domain protein, which is essential for activation of CATSPER channel that regulates sperm motility [111].…”