Structure of IZUMO1–JUNO reveals sperm–oocyte recognition during mammalian fertilization

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Abstract

Fertilization is a fundamental process in sexual reproduction, creating a new individual through the combination of male and female gametes1,2,3,4. The IZUMO1 sperm membrane protein5and its counterpart oocyte receptor JUNO6have been identified as essential factors for sperm–oocyte interaction and fusion. However, the mechanism underlying their specific recognition remains poorly defined. Here, we show the crystal structures of human IZUMO1, JUNO and the IZUMO1–JUNO complex, establishing the structural basis for the IZUMO1–JUNO-mediated sperm–oocyte interaction. IZUMO1 exhibits an elongated rod-shaped structure comprised of a helical bundle IZUMO domain and an immunoglobulin-like domain that are each firmly anchored to an intervening β-hairpin region through conserved disulfide bonds. The central β-hairpin region of IZUMO1 provides the main platform for JUNO binding, while the surface located behind the putative JUNO ligand binding pocket is involved in IZUMO1 binding. Structure-based mutagenesis analysis confirms the biological importance of the IZUMO1–JUNO interaction. This structure provides a major step towards elucidating an essential phase of fertilization and it will contribute to the development of new therapeutic interventions for fertility, such as contraceptive agents.

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