A team of international scientists has discovered exactly how a human egg captures a sperm in the fertilization process, which could lead to better fertility drugs.

The researchers found that a sugar chain, called sialyl-lewis-x sequence or SLeX, is responsible for the binding between the egg and the sperm, and it is found in high frequency on the surface of the egg's coat.

Scientists already know that a sperm identifies an egg when proteins on the head of the sperm match a variety of sugars in the egg's outer coating. Once a successful match has been made, the outer surfaces of the egg and sperm bind together before merging, and the sperm is able to release its DNA to fertilize the egg.

For years scientists have puzzled over which specific sugar molecule led to the binding of the egg and sperm. Using ultra-sensitive mass-spectrometric imaging technology, the researchers were able to study the binding process. They concluded that a sugar chain called the sialyl-lewis-x sequence, or SLeX, which was abundant on the surface of the human egg, specifically binds sperm to an egg.

A part of the research team then tested this theory by using the outer coats of unfertilized non-living human eggs from in vitro-fertilization patients. The patients gave their consent for the research. A chemical that stops SLeX from binding was added to half of the eggs and then all the eggs were introduced to sperm. Fewer sperm bound themselves to the eggs that were treated with the chemical than the ones that were untreated, reports BioScholar.

The research was conducted by scientists from the Department of Life Sciences at Imperial College London, University of Missouri, the University of Hong Kong, Academia Sinica in Taiwan and Imperial College London.

The details we've discovered here fill in a huge gap in our knowledge of fertility and we hope they will ultimately help many of those people who currently cannot conceive, said Anne Dell of Imperial College London, who worked on the study.

Dell said that the study was an enormously difficult task as human eggs are very tiny about the size of a full stop. The scientists didn't have much material to work with, Dell added.

The team hopes that the research can help them to get a better understanding of human infertility and could lead to improved fertility drugs.

Dr. Poh-Choo Pang of Imperial College London, who also worked on the study, said that even though clinical treatments derived from the study are still away off, it would open up new possibilities for understanding and addressing fertility problems.

The study was published in the journal Science.

The World Health Organization estimates that infertility affects up to 15 percent of reproductive-aged couples around the world and almost one in every seven couples in Britain has problems conceiving a child for various reasons, many of which remain unexplained by medical science, reports Reuters.

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