"Catch-bond" mechanism decoded This is why the connection between sperm and egg cells is the strongest
Researchers at ETH Zurich and the University of Basel have described one of the strongest known biological bonds - between sperm and egg. Their discovery could help to better understand certain forms of infertility in the future.
20.10.2025, 11:06
25.10.2025, 22:32
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- Researchers at ETH Zurich and the University of Basel have discovered that sperm and egg cells form a particularly strong bond via the proteins Izumo and Juno using a so-called "catch-bond" mechanism.
- This bond becomes even stronger under tensile forces - a rare phenomenon in biology - and is one of the strongest known biological bonds.
- A mutation in the Juno protein, which affects around one in 600 women, can weaken this bond and promote infertility; the findings could make genetic tests or therapies possible in the future.
During fertilization, the sperm and egg cling to each other with unusual strength. Researchers at ETH Zurich and the University of Basel have now deciphered how this strong bond works.
According to a press release issued by ETH Zurich on Monday, this bond is one of the strongest biological bonds known to date. It is formed via the proteins Izumo on the sperm and Juno on the egg cell. As the research team reports in the journal "Nature Communications", this interaction follows a so-called "catch-bond" mechanism: the stronger it is pulled, the more firmly it holds.
The researchers have thus discovered a special feature that rarely occurs in biology. Normally, bonds between molecules weaken when mechanical forces act on them.
Medical significance
The discovery also has medical significance: a genetic mutation in the Juno protein, which affects around one in 600 women worldwide, weakens this bond. This could explain why some women experience infertility despite having healthy egg cells.
In the long term, the results could help to develop genetic tests or therapies against certain forms of infertility, ETH Zurich writes in its press release.
For their study, the researchers examined the proteins in the laboratory using an atomic force microscope. They pulled the molecules apart in a controlled manner and measured the forces that hold them together. Computer simulations confirmed that the proteins twist slightly under tension and thus form new atomic contacts - this makes the bond even stronger.
Under tension, the bond between Juno and Izumo is actually one of the strongest that exists in the realm of multicellular organisms, as the researchers' measurements showed. There are similarly strong bonds between proteins in muscle fibers that prevent the muscle fibers from tearing.
