AsianScientist (Aug. 17, 2016) – Japanese researchers have described the mechanism of the interaction between egg and sperm on a molecular level, with the help of the crystal structure of JUNO protein, an egg surface protein essential for fertilization.
The study, published in Nature Communications, was led by co-corresponding authors Professor Osamu Nureki, of the Graduate School of Science at the University of Tokyo, and Professor Masahito Ikawa, of the Research Institute for Microbial Diseases at Osaka University.
Fertilization is a critical process for starting new life and begins with the fusion between sperm and egg. Here, two proteins play an important role: JUNO protein, which is named after the Roman goddess of fertility and marriage, and IZUMO1, which is named after the Japanese marriage shrine. IZUMO1 on the spermatozoon and the IZUMO1 counter-receptor on the egg, JUNO, help to form an intercellular bridge, and deletion of either gene leads to the failure of gamete membrane fusion.
To study the molecular mechanism by which JUNO specifically recognizes IZUMO1, the researchers crystallized the mouse JUNO protein and determined the crystal structure of JUNO by molecular replacement at 2.3 ångström resolution.
Then, using JUNO-deleted eggs, the group examined the role of amino acid residues in fertilization. As a result of the mutational analysis, an amino acid residue in JUNO called W62 was determined to be essential for the interaction with IZUMO1.
The researchers believe that their studies will provide a framework toward a better understanding of the mechanism behind fertilization.
The article can be found at: Kato et al. (2016) Structural and Functional Insights into IZUMO1 Recognition by JUNO in Mammalian Fertilization.
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Source: Osaka University.
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