Modifications of acrosome reaction-inducing egg coat glycans

The exocytotic acrosome reaction (AR) is a mandatory step in sperm-egg interactions in most metazoans. The molecules present in egg coats play crucial roles in AR induction. These signaling molecules are mainly complex carbohydrates, which are either protein-bound or -free. The structural elucidation of these glycans is in progress. The new knowledge gained should lead to new insights into the molecular mechanisms of AR induction. The modifications of the AR-inducing glycans involve O-glycosylation, fucosylation, sulfation and sialylation. These modifications are conserved from the lowest deuterostomes to the highest vertebrates. The evidence suggests that the AR is mediated by a carbohydrate-protein interaction. Here the primary structures and important features of these AR inducing carbohydrates present in both invertebrate and vertebrate egg coats are reviewed.