Molecule from ancient bacteria-like cells may shed new light on sexual reproduction
Crystal structure of Fusexin1. Archaeal species with fusexins thrive in hypersaline environments like salt lakes, oceans and salterns. Credit: Luca Jovine.

Egg-sperm fusion, a key feature of sexual reproduction in plants and animals, may have originated from an ancient form of genetic exchange. An entirely new perspective on the evolution of sex may be opened by the results.

"Archaeal proteins with fusion activity might help us to understand how cells evolved from simple forms to complex life forms, and how sexual reproduction evolved from simple forms to complex life forms," says the researcher.

Sexual reproduction ends with the fusion of egg and sperm, specialized cells that carry the genetic information for the next generation. Plants and animals use fusogens to control when and where cell fusion occurs.

A molecule is an important ancestral molecule.

According to a new study, archaea, the cells that are thought to have originated more than 3 billion years ago, can contain a type of fusogen that has previously been found in viruses, plants and arthropods.

Computational evolutionary biology, AlphaFold-based protein modeling, X-ray crystallography, and functional studies were used by the researchers to show that Fsx1 is a legit fusogen. It is able to promote cell-cell fusion when expressed in other cell types because it is similar to the HAP2 fusogen.

For more than 150 years, gamete fusion has fascinated humankind. We wondered if this key molecule came from a virus or if it was used in plants and animals.

The discovery that ancient creatures like archaea can also contain a HAP2-likeprotein now raises a third intriguing possibility that is related to the ancestral molecule from which viral, plant, and invertebrate animal fusogens derive.

Sex's beginning.

The study was a collaboration between academic research groups from Israel, Argentina, Uruguay, and Switzerland, as well as the European Synchrotron Radiation Facility in France and the UK-based artificial intelligence company DeepMind.

The next step will be to figure out what Fsx1 and HAP2 are doing in nature if they combine archaeal cells. In order to establish the origin of Fsx1 and HAP2, parallel studies are needed.

More information: David Moi et al, Discovery of archaeal fusexins homologous to eukaryotic HAP2/GCS1 gamete fusion proteins, Nature Communications (2022). DOI: 10.1038/s41467-022-31564-1 Journal information: Nature Communications