Human sperm TMEM95 binds eggs and facilitates membrane fusion

Tang, Shaogeng; Lu, Yonggang; Skinner, Will M.; Sanyal, Mrinmoy; Lishko, Polina V.; Ikawa, Masahito; Kim, Peter S.

doi:10.1101/2022.06.10.495573

Cited by 5 publications

(3 citation statements)

References 25 publications

(43 reference statements)

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“…The IZUMO1 monoclonal antibodies were generated from mouse hybridoma and characterized as previously described (47). Briefly, IZUMO1 antibodies 4E04 and 6F02 belong to the murine IgG1 isotype with kappa light chain.…”

Section: Methodsmentioning

confidence: 99%

Mitochondrial uncouplers impair human sperm motility without altering ATP content

Skinner

Petersen

Unger

et al. 2022

Preprint

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Sperm motility is necessary for successful fertilization, but there remains controversy about whether human sperm motility is primarily powered by glycolysis or oxidative phosphorylation. To evaluate the plausibility of reducing human sperm mitochondrial ATP production as an avenue for contraceptive development, we treated human sperm with small-molecule mitochondrial uncouplers, which reduce mitochondrial membrane potential by inducing passive proton flow, and evaluated the effects on a variety of physiological processes that are critical for fertilization. We also sought to clarify the subcellular localization of Adenosine Nucleotide Translocator 4 (ANT4), a gamete-specific protein that has been suggested as a contraceptive target. We determined that ANT4 is mitochondrially localized, that induced mitochondrial uncoupling can be partially mediated by the ANT family, and that two uncouplers, Niclosamide Ethanolamine and BAM15, significantly decreased sperm progressive motility. However, these uncouplers did not reduce sperm ATP content or impair other physiological processes, implying that human sperm can rely on glycolysis for ATP production in the absence of functional mitochondria. Thus, since certain mitochondrial uncouplers impair motility through ATP-independent mechanisms, they could be useful ingredients in on-demand, vaginally-applied contraceptives. However, systemically delivered contraceptives that target sperm mitochondria to reduce their ATP production would need to be paired with sperm-specific glycolysis inhibitors.

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Section: Methodsmentioning

confidence: 99%

Mitochondrial uncouplers impair human sperm motility without altering ATP content

Skinner

Petersen

Unger

et al. 2022

Preprint

Self Cite

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“…Mammalian cells expressing ectopic IZUMO1 can bind to but not to fuse with JUNO-expressing mouse eggs, which is consistent with a main role for IZUMO1-JUNO in sperm-egg binding 21,31,32 . Although IZUMO1 is similar to SPACA6 and TMEM95 at the structural level [33][34][35] , recombinant human SPACA6 and TMEM95 do not bind to human JUNO in solution 34,35 . Thus, despite the identification of various essential factors in vertebrates, the precise molecular interactions responsible for sperm-egg binding and fusion remain poorly understood.…”

Section: Introductionmentioning

confidence: 94%

“…1D). The conserved Nterminal four-helix bundle of Izumo1 and Spaca6 34,35 is absent in Tmem81. Interestingly, apart from Dcst1/2 proteins, which are also present outside of vertebrates, Tmem81 is the most conserved vertebrate fertilization factor identified to date (Suppl.…”

Section: Alphafold-multimer Predicts the Formation Of An Izumo1-spaca...mentioning

confidence: 99%

A conserved fertilization complex of Izumo1, Spaca6, and Tmem81 mediates sperm-egg interaction in vertebrates

Deneke

Blaha

et al. 2023

Preprint

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Fertilization, the fusion of sperm and egg, is essential for sexual reproduction. While several proteins have been demonstrated to be essential for the binding and fusion of gametes in vertebrates, the molecular mechanisms driving this key process are poorly understood. Here, we performed a protein interaction screen using AlphaFold-Multimer to uncover protein-protein interactions in fertilization. This screen resulted in the prediction of a trimeric complex composed of the essential fertilization factors Izumo1 and Spaca6, and Tmem81, a protein previously not implicated in fertilization. We show that Tmem81 is a conserved, testis-expressed transmembrane protein that is evolutionarily related to Izumo1 and Spaca6 and is essential for male fertility in fish and mice. Consistent with trimer formation in vivo, zebrafish izumo1-/-, spaca6-/-, and tmem81-/- mutants exhibit the same sperm-egg binding defect and show co-depletion of all three proteins in sperm. Moreover, we provide experimental evidence that Izumo1, Spaca6, and Tmem81 interact in zebrafish sperm. Strikingly, the Izumo1-Spaca6 interaction is predicted to form a cleft that serves as a binding site for Bouncer, the only identified egg protein essential for fertilization in zebrafish. Together, these results provide compelling evidence for a conserved sperm factor complex in vertebrates that forms a specific interface for the sperm-egg interaction required for successful fertilization.

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SPACA6 ectodomain structure reveals a conserved superfamily of gamete fusion-associated proteins

et al. 2022

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SPACA6 is a sperm-expressed surface protein that is critical for gamete fusion during mammalian sexual reproduction. Despite this fundamental role, little is known about how SPACA6 specifically functions. We elucidated the crystal structure of the SPACA6 ectodomain at 2.2-Å resolution, revealing a two-domain protein containing a four-helix bundle and Ig-like β-sandwich connected via a quasi-flexible linker. This structure is reminiscent of IZUMO1, another gamete fusion-associated protein, making SPACA6 and IZUMO1 founding members of a superfamily of fertilization-associated proteins, herein dubbed the IST superfamily. The IST superfamily is defined structurally by its distorted four-helix bundle and a pair of disulfide-bonded CXXC motifs. A structure-based search of the AlphaFold human proteome identified more protein members to this superfamily; remarkably, many of these proteins are linked to gamete fusion. The SPACA6 structure and its connection to other IST-superfamily members provide a missing link in our knowledge of mammalian gamete fusion.

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Human sperm TMEM95 binds eggs and facilitates membrane fusion

Cited by 5 publications

References 25 publications

Mitochondrial uncouplers impair human sperm motility without altering ATP content

Mitochondrial uncouplers impair human sperm motility without altering ATP content

A conserved fertilization complex of Izumo1, Spaca6, and Tmem81 mediates sperm-egg interaction in vertebrates

SPACA6 ectodomain structure reveals a conserved superfamily of gamete fusion-associated proteins

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