Protein Tyrosine Phosphorylation and Signal Transduction During Capacitation-Acrosome Reaction and Zona Pellucida Binding in Human Sperm

Abstract

During capacitation and acrosome reaction of human sperm, 7–14 proteins are phosphorylated, and two of these proteins (95 and 51 kD) are phosphorylated at tyrosine resides. The sperm proteins that bind ZP3 in humans have molecular identities of 95, 63, 51 (FA-1 antigen), and 14–18 kD, respectively. Three of these molecules, 95-, 51-, and 14–18-kD proteins, undergo tyrosine phosphorylation, and 51 kD (FA-1 antigen) also undergoes autophosphorylation. Many of the sperm proteins that participate in ZP binding are also involved in capacitation/acrosome reaction. These findings indicate a vital role of protein tyrosine phosphorylation and tyrosine receptor kinases in sperm capacitation, acrosome reaction, and ZP binding. Since tyrosine phosphorylation is the primary, or even exclusive, indication of signal transduction, it would appear that a signal transduction pathway is involved in these processes. However, the exact mechanism requires further study.

Key Words:

• acrosome reaction
• capacitation
• fertilization
• signal transduction
• sperm
• tyrosine kinase
• tyrosine phosphorylation