An international team of researchers claimed they've learned how a human egg captures an incoming sperm for fertilization, a discovery that may help couples who are having infertility issues.

The researchers said they have found that a sugar chain known as the sialyl-lewis-x sequence (SLeX) makes the outer coat of the egg sticky, which helps in binding the egg and the sperm, according to media reports. This observation has filled in a huge gap in man's understanding of fertility and also provides hope for eventually  helping couples who currently cannot conceive.

Professor Anne Dell, from the Department of Life Sciences at Imperial College London, led the study. She was accompanied by a team of researchers from the University of Missouri, the University of Hong Kong, Academia Sinica in Taiwan and Imperial College London.

This exciting research is providing the first insights into the molecular events occurring at the very beginning of human life, Dell told BioScholar. 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.

A sperm is able to identify an egg when the proteins on the head meet the different sugars in the egg's outer coat.

When a sperm and an egg match, these outer surfaces bind together before merging, and the sperm then release its DNA to fertilize the egg.

But researchers have wondered for years which specific sugar molecule led to the binding of the sperm and the egg.

The team used mass-spectrometric imaging technology to examine the binding process, and from their observation, they deduced that SLeX must be responsible since it's plentiful on the egg's outer coat.

The Hong Kong research team next tested this theory by getting the outer coats of fertilized and unfertilized eggs from in vitro-fertilization patients, who gave the researchers consent to do so. They treated one half of the empty coat with chemical that stopped the SLeX from binding. And when sperm was released to the treated and untreated halves of the outer coat. Fewer sperm bound to the treated half.

Gary Clark, co-author of the study from the University of Missouri School of Medicine, told DailyTech that the team proposed a human sperm-binding model that involved SLeX molecules in 1992, and was happy to see that this theory was finally confirmed. 

Unraveling the composition of the sugar coat that shrouds the human egg is the culmination of many years of painstaking research by mass spectrometry colleagues at Imperial, Dell told DailyTech. This endeavor was an enormously difficult task because human eggs are very tiny — about the size of a full stop — so we didn't have much material to work with.

The World Health Organisation said infertility affects about 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.

We hope that our study will open up new possibilities for understanding and addressing the fertility problems that many couples face, said Dr. Poh-Choo Pang, lead author from the Department of Life Sciences at Imperial College London, as reported by DailyTech. Although clinical treatments are still a way off, we are very excited about the new research into fertility that we hope will now be possible, building on our work.