Sperm surface proteins in mammalian fertilization

Area of Science:

• Reproductive Biology
• Biochemistry
• Animal Science

Background:

• Boar seminal plasma contains various proteins that influence sperm function.
• Spermadhesins are a class of seminal proteins known to interact with sperm.
• The role of protein aggregates versus monomers in seminal plasma is not fully understood.

Purpose of the Study:

• To characterize the protein composition of boar seminal plasma fractions.
• To investigate the interactions of these proteins and their aggregates with the zona pellucida and sperm.
• To determine the physiological relevance of seminal protein aggregates in fertilization.

Main Methods:

• Gel chromatography (Sephadex G-75 SF) to separate seminal plasma proteins into fractions.
• Reverse-phase high-performance liquid chromatography (RP-HPLC) for further purification.
• N-terminal sequencing to identify protein components.
• Binding assays with acidic polysaccharides, porcine zona pellucida glycoproteins, and spermatozoa.

Main Results:

• High-molecular-weight aggregates comprised DQH sperm surface protein and spermadhesins (AQN, AWN, PSP II).
• Monomeric spermadhesins were found in very low amounts.
• Aggregates and monomeric proteins interacted with acidic polysaccharides and phosphorylcholine; aggregates showed stronger binding to boar epididymal spermatozoa.
• AWN-containing aggregates and proteins exhibited the strongest interaction with porcine zona pellucida glycoproteins.

Conclusions:

• Seminal plasma protein aggregates (DQH, AQN, AWN, PSP II) are the predominant forms in vivo.
• These aggregates, rather than individual proteins, are likely involved in sperm surface coating.
• Protein aggregates play a significant role in sperm capacitation and the initial binding of spermatozoa to the ovum's zona pellucida.