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Molecular architecture of the human sperm IZUMO1 and egg JUNO fertilization complex

Nature volume 534, pages 562565 (23 June 2016) | Download Citation

Abstract

Fertilization is an essential biological process in sexual reproduction and comprises a series of molecular interactions between the sperm and egg1,2. The fusion of the haploid spermatozoon and oocyte is the culminating event in mammalian fertilization, enabling the creation of a new, genetically distinct diploid organism3,4. The merger of two gametes is achieved through a two-step mechanism in which the sperm protein IZUMO1 on the equatorial segment of the acrosome-reacted sperm recognizes its receptor, JUNO, on the egg surface4,5,6. This recognition is followed by the fusion of the two plasma membranes. IZUMO1 and JUNO proteins are indispensable for fertilization, as constitutive knockdown of either protein results in mice that are healthy but infertile5,6. Despite their central importance in reproductive medicine, the molecular architectures of these proteins and the details of their functional roles in fertilization are not known. Here we present the crystal structures of human IZUMO1 and JUNO in unbound and bound conformations. The human IZUMO1 structure exhibits a distinct boomerang shape and provides structural insights into the IZUMO family of proteins7. Human IZUMO1 forms a high-affinity complex with JUNO and undergoes a major conformational change within its N-terminal domain upon binding to the egg-surface receptor. Our results provide insights into the molecular basis of sperm–egg recognition, cross-species fertilization, and the barrier to polyspermy, thereby promising benefits for the rational development of non-hormonal contraceptives and fertility treatments for humans and other mammals.

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Accessions

Data deposits

Atomic coordinates and structure factors have been deposited in the Protein Data Bank under accession codes: 5F4E (IZUMO122–254–JUNO20–228 complex); 5F4Q (JUNO20–228); 5F4T (IZUMO122–254); 5F4V (IZUMO122–268).

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Acknowledgements

This work was supported by a CIHR Operating Grant (MOP-115066), an NSERC Discovery Grant (RGPIN 435607-13), an Ontario Early Researcher Award (ER-13-09-116), and a Canada Research Chair to J.E.L. S.L. is supported by grants from NIH (1U19AI117905, R01 GM020501 and R01 AI101436). Support for stipends was provided by University of Toronto and Ontario Graduate Scholarships to H.A. and an NSERC USRA to A.T. We thank W. Houry, T. Moraes and C. Spring for access to circular dichroism, SEC–MALS and SPR systems, respectively. This work is based upon X-ray data collected at beamline 08ID-1 at the Canadian Light Source (CLS) and Structural Genomics Consortium (SGC), and SAXS data acquired at the Advanced Light Source (ALS) SIBYLS beamline 12.3.1. The CLS is supported by NSERC, National Research Council of Canada, CIHR, the Province of Saskatchewan, Western Economic Diversification Canada, and the University of Saskatchewan. The ALS is a national user facility operated by Lawrence Berkeley National Laboratory on behalf of the US Department of Energy (Office of Basic Energy Sciences) through the Integrated Diffraction Analysis Technologies program (DE-AC02-05CH11231), supported by the DOE Office of Biological and Environmental Research; additional support comes from NIH project MINOS (R01GM105404). We thank F. Azimi, J. Cook, A. Dong and N. Ly for technical support, and E. Ollmann Saphire, A. S. Rocca and G. Bikopoulos for critical reading of the manuscript.

Author information

Affiliations

  1. Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario M5S 1A8, Canada

    • Halil Aydin
    • , Azmiri Sultana
    • , Annoj Thavalingam
    •  & Jeffrey E. Lee
  2. Department of Medicine, University of California, San Diego, La Jolla, California 92093, USA

    • Sheng Li

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Contributions

H.A. designed the project, performed all the cloning, mutagenesis, expression, purification, biophysical characterization and crystallization experiments, collected synchrotron X-ray diffraction data, and determined the crystal structures and SAXS reconstructions. A.S. assisted with BLI and SPR experiments and provided crystallographic guidance for refinement and validation of the crystal structures. A.T. assisted with protein expression and purification. H.A. prepared the samples and S.L. performed and analysed the DXMS data. J.E.L supervised the research and assisted with BLI experiments. H.A. and J.E.L. analysed and discussed all results, and wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Jeffrey E. Lee.

Reviewer Information Nature thanks K. Melcher, M. Okabe and other anonymous reviewer(s) for their contribution to the peer review of this work.

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https://doi.org/10.1038/nature18595

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