The structure of sperm Izumo1 reveals unexpected similarities with Plasmodium invasion proteins.Nishimura, K., Han, L., Bianchi, E., Wright, G.J., de Sanctis, D., Jovine, L.
(2016) Curr.Biol. 26: R661-R662
- PubMed: 27374339
- DOI: 10.1016/j.cub.2016.06.028
- PubMed Abstract:
- The immunoglobulin superfamily protein Izumo is required for sperm to fuse with eggs.
Inoue, N.,Ikawa, M.,Isotani, A.,Okabe, M.
(2005) Nature 434: 234
- Juno is the egg Izumo receptor and is essential for mammalian fertilization.
Bianchi, E.,Doe, B.,Goulding, D.,Wright, G.J.
(2014) Nature 508: 483
- Divergent evolution of vitamin B9 binding underlies Juno-mediated adhesion of mammalian gametes.
Han, L.,Nishimura, K.,Sadat Al Hosseini, H.,Bianchi, E.,Wright, G.J.,Jovine, L.
(2016) Curr. Biol. 26: R100
Fertilization, the culminating event in sexual reproduction, occurs when haploid sperm and egg recognize each other and fuse to form a diploid zygote. In mammals this process critically depends on the interaction between Izumo1, a protein exposed on ...
Fertilization, the culminating event in sexual reproduction, occurs when haploid sperm and egg recognize each other and fuse to form a diploid zygote. In mammals this process critically depends on the interaction between Izumo1, a protein exposed on the equatorial segment of acrosome-reacted sperm, and the egg plasma-membrane-anchored receptor Juno [1,2]. The molecular mechanism triggering gamete fusion is unresolved because both Izumo1 and Juno lack sequence similarity to known membrane fusogens. Here we report the crystal structure of Izumo1, which reveals a membrane distal region composed of a four-helix bundle connected to a carboxy-terminal immunoglobulin (Ig)-like domain through a β-hairpin stabilized by disulfide bonds. Remarkably, different regions of Izumo1 display significant structural similarities to two proteins expressed by the invasive sporozoite stage of Plasmodium parasites: SPECT1, which is essential for host cell traversal and hepatocyte invasion ; and TRAP, which is necessary for gliding motility and invasion . These observations suggest a link between the molecular mechanisms underlying host cell invasion by the malaria parasite and gamete membrane fusion at fertilization.
Department of Biosciences and Nutrition & Center for Innovative Medicine, Karolinska Institutet, Huddinge, SE-141 83, Sweden.