A novel study in the scientific journal Molecular Biology and Evolution draws a completely unexpected link between reproductive proteins in humans and proteins involved in fertilization in invertebrates, as well as mating between haploid cells in yeast. Because human and yeast are separated by 1 billion years of evolution, these findings may have important implications for our understanding of the molecular mechanisms underlying sex, and how they originated.
The lead author of the current study, Dr Luca Jovine at Karolinska Institutet in Sweden, has earlier been able to describe the complete 3D structure of ZP3, a conserved vertebrate egg protein that acts as receptor for sperm at the beginning of fertilization. With this new knowledge, Luca Jovine and his team add another dimension to their research.
Species-specific interaction between egg and sperm -- a fundamental biological event that marks the beginning of fertilization in multicellular organisms -- parallels the binding between haploid cells of opposite mating type in unicellular eukaryotes such as yeast. However, because of the lack of sequence similarity between sperm-binding regions of invertebrate and vertebrate egg coat proteins, these interactions were thought to rely on entirely different molecular entities.
In the current article the scientists argue that these recognition systems are, in fact, related. Specifically, they suggest that -- despite being separated by 0.6-1 billion years of evolution -- functionally essential regions of a mollusc sperm receptor and a yeast mating protein might adopt a three-dimensional conformation similar to that of egg proteins that mediate the binding between gametes in humans.
"Since pathogenic yeast species such as Candida albicans use a corresponding protein region to bind human endothelial and epithelial cells, the information provided by these findings could also be relevant for infection medicine," says Luca Jovine.
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