Could multiple low-affinity bonds mediate primary sperm-zona pellucida binding?

The current model for primary sperm binding to the zona pellucida is that a cell-surface sperm protein binds with high affinity in an order-specific manner to one of the zona pellucida proteins, ZP3. However, the molecular details of primary sperm-zona pellucida binding remain elusive. A possible revised model is that multiple low-affinity bonds between spermatozoa and the zona pellucida may be sufficient for primary binding. The avidity of several low-affinity bonds can exceed that of a single high-affinity bond, which is sufficient to tether a motile spermatozoon. A mechanism involving multiple low-affinity bonds could account for some of the difficulties in elucidating primary sperm-zona pellucida interactions.