During fertilization in mammals, the sperm-associated protein IZUMO1 recognizes the receptor JUNO at the egg surface, but the structural details of the interactions were previously unknown. In two papers published in this issue of Nature, Halil Aydin et al. and Umeharu Ohto et al. present the first atomic-resolution structures of human IZUMO1 and JUNO in unbound and bound conformations. Aydin et al. describe a boomerang-shaped structure for IZUMO1, and their data suggest that IZUMO1 undergoes a major conformational change on binding with high affinity to JUNO. Ohto et al. report an elongated rod-shaped structure for IZUMO1, comprising a helical bundle IZUMO domain connected by a β-hairpin region to an immunoglobulin-like domain. Mutational studies of the IZUMO1–JUNO interface by both groups reveal the structural determinants required for binding. These results provide data that can inform the development of novel non-hormonal contraceptives and fertility treatments.
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