Scientists find protein that unites sperm and egg

Erika Check Hayden in Nature:

Scientists have identified a long-sought fertility protein that allows sperm to dock to the surface of an egg. The finding, an important step in understanding the process that enables conception, could eventually spawn new forms of birth control and treatments for infertility. “It’s very important, because we now know two of the proteins that are responsible for the binding of sperm to the egg,” says Paul Wassarman, a biochemist and developmental biologist at the Icahn School of Medicine at Mount Sinai in New York. The work, published today in Nature¹, was led by Gavin Wright, a biochemist at the Wellcome Trust Sanger Institute in Hinxton, UK. He and his team were looking for a counterpart to a protein called Izumo1, discovered in 2005 on the surface of sperm cells².

Scientists knew that Izumo1 allowed sperm to join to an egg to begin the process of fertilization. But nobody knew what protein on the surface of the egg attached to Izumo1. Identifying the proteins involved in the joining step has been difficult because the molecules tend to bind quite weakly to each other. So Wright and his team devised a way to cluster Izumo1 proteins, then searching for the egg-cell proteins that would bind to the clusters in cell culture. Wright compares the technique to constructing a Velcro fastener out of many individual fabric loops: “Each small hook adheres weakly, but when [they are] clustered in an array, even the most fleeting interactions are stabilized and can therefore be detected,” he says. Using this method, the team hooked a protein called folate receptor 4 that is found on the surface of the mouse egg cell. Wright’s team propose renaming the egg protein Juno, after the Roman goddess of fertility and marriage. Izumo1 is also named after a cultural symbol of reproduction — a Japanese marriage shrine.

More here.