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Curr Biol. 2016 Jul 25;26(14):R661-2. doi: 10.1016/j.cub.2016.06.028. Epub 2016 Jun 30.

The structure of sperm Izumo1 reveals unexpected similarities with Plasmodium invasion proteins.

Author information

1
Department of Biosciences and Nutrition & Center for Innovative Medicine, Karolinska Institutet, Huddinge, SE-141 83, Sweden.
2
Cell Surface Signalling Laboratory, Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK.
3
ESRF - The European Synchrotron, Grenoble 38000, France.
4
Department of Biosciences and Nutrition & Center for Innovative Medicine, Karolinska Institutet, Huddinge, SE-141 83, Sweden. Electronic address: luca.jovine@ki.se.

Abstract

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 [3]; and TRAP, which is necessary for gliding motility and invasion [4]. These observations suggest a link between the molecular mechanisms underlying host cell invasion by the malaria parasite and gamete membrane fusion at fertilization.

PMID:
27374339
PMCID:
PMC4963209
DOI:
10.1016/j.cub.2016.06.028
[Indexed for MEDLINE]
Free PMC Article

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