A PROTEIN that plays a crucial role in conception could be the key to creating a contraceptive that doesn’t tinker with a woman’s hormones.

The coating of mammalian eggs contains a protein called ZP3, which sperm must bind to if they are to burrow through the coating and fertilise the egg. Female mice engineered to lack ZP3 do not have this coating, making them infertile, while women with abnormal ZP3 may also suffer fertility problems.

Luca Jovine at the Karolinska Institute in Huddinge, Sweden, and his colleagues have used X-ray crystallography to work out the chemical structure of a stretch …