A 70 kDa protein is transferred from the outer acrsomal to the plasma membrane during capacitation

Abstract

Bull sperm plasma and outer acrosomal membranes were analyzed by SDS-PAGE. Analysis of the plasma membrane proteins revealed the presence of a 70 kDa band the prominence of which is enhanced after capacitation. This protein was found to bind to zona pellucida intact oocytes. PAGE analysis of outer acrosomal membrane proteins also reveals the presence of a 70 kDa band, but its prominence decreases after capacitation. This protein also binds to zona pellucida intact oocytes. Futhermore, the 70 kDa outer acrosomal membrane protein is recognized in Western blot analysis by antibodies to plasma membrane proteins and vice versa. The results indicate that the 70 kDa acrosomal and plasma membrane proteins are the same. This 70 kDa protein would thus be a zona pellucida binding protein which is initially stored in the outer acrosomal membrane and transferred to the plasma membrane during capacitation, enabling it to function in egg-sperm binding.

Identification of Extracellular Signal-regulated Kinase 1/2 and p38 MAPK as Regulators of Human Sperm Motility and Acrosome Reaction and as Predictors of Poor Spermatozoan Quality

“…ARHGAP6 has two independent functions as follows: a specific GAP for RhoA, and a promoter of actin remodeling (45). As RhoA is implicated in cell motility (55,56) and actin remodeling is implicated in hyperactivated motility and the acrosome reaction (46,47), phosphorylation of sperm ARHGAP6 by ERK may be involved in sperm motility, capacitation, and acrosome reaction via RhoA. Other potential substrates are the dyneins, the sperm motor molecules of the axoneme (48), known to be phosphorylated during activation (49).…”

Role and Regulation of Sperm Gelsolin Prior to Fertilization

“…It appears that actin polymerization during sperm capacitation depends on phospholipase D activity, which is regulated by the cross-talk between PKA and protein kinase C (PKC) (1,28). Moreover, we showed elsewhere that PIP 2 (4,5) , the cofactor for phospholipase D activation and F-actin production during sperm capacitation, is mediated by phospha-tidylinositol 4-kinase (PI4K) but not by phosphatidylinositol 3-kinase (PI3K) activity (29).…”

“…Another important process that occurs during sperm capacitation is actin polymerization; however, at the end of the capacitation, the polymers must disperse to achieve the AR (3). It has been suggested that an increase in F-actin creates a network between the plasma and the outer acrosomal membranes, and the dispersion of F-actin between the two membranes is needed to enable the AR (3)(4)(5)(6).…”

“…Phosphoinositides release gelsolin from actin filament ends, providing sites for actin assembly (14 -17). In vitro studies suggested that gelsolin is phosphorylated by pp60(c-SRC) and that this phosphorylation is enhanced by phosphoinositide 4,5-bisphosphate (PIP 2 (4,5) ) (18) and can interfere with the binding of gelsolin to the actin filaments (19). Previous work identified SRC in human spermatozoa, and it appears to be involved in regulating sperm capacitation, calcium fluxes, tyrosine phosphorylation, and the acrosome reaction (20).…”

“…It was suggested that EGFR is phosphorylated at the SRC-specific site, suggesting that SRC is active during capacitation (21,22). Additionally, EGFR-mediated signaling is known to activate phospholipase C␥ (PLC␥), to hydrolyze PIP 2 (4,5) , and to cause the subsequent release of PIP 2(4,5) -bound proteins. In vitro studies have shown that gelsolin modulates the activity of several signaling enzymes, including PLC and phospholipase D through interactions with PIP 2(4,5) (23)(24)(25)(26)(27)).…”