Aggregated and monomeric forms of proteins in boar seminal plasma: Characterization and binding properties

Boar seminal plasma was separated into five protein fractions (I-V) (>100, 55, 45, 30, 5-15 kDa) by gel filtration chromatography on Sephadex G-75 SF at pH 7.4. RP HPLC of protein fractions I-V and N-terminal sequencing of th eir individual components revealed that high-molecular-weight aggregates co nsisted mainly of DQH sperm surface protein and AQN, AWN, PSP II spermadhes ins, while fraction IV consisted of heterodimers of PSP spermadhesins only. Spermadhesins as monomers were present in seminal plasma in a very low amo unt. Biotinylated fractions I-IV containing AWN, AQN, DQH, and PSP proteins were bound to boar epididymal and ejaculated spermatozoa with the same eff iciency, Aggregates containing AWN, AQN, DQH, PSP II proteins (fractions I- III) and their HPLC-separated monomeric forms interacted with phosphorylcho line. Aggregates containing the DQH protein and AWN spermadhesins as well a s their separated monomeric proteins interacted strongly with acidic polysa ccharides. PSP II interacted with some acidic polysaccharides, while the fr action IV corresponding to heterodimer PSP I/PSP II did not show any bindin g to acidic polysaccharides and zona pellucida, Fractions I-III showed affi nity to cholesterol, The strongest interaction was observed between biotiny lated glycoproteins of porcine zona pellucida and AWN 1-containing aggregat es and separated proteins. AQN 1 spermadhesin efectivelly blocked the sperm binding to oocytes. These results suggest that under physiological conditi ons, the aggregated forms of seminal plasma proteins (DQH, AQN, AWN, PSP II ) rather than the individual proteins might take part in coating the sperm surface, in sperm capacitation and in primary binding of spermatozoa to zon a pellucida of the ovum.