Calcium-binding proteins of boar spermatozoan plasma membranes: identification and partial characterization

Calcium-binding proteins (CBPs) of boar spermatozoa and boar seminal plasma were identified by using a 45Ca overlay technique to detect these proteins on transblots of PAGE-separated proteins. A single CBP (Mr approximately 300 kDa) was detected in seminal plasma. This protein binds specifically to the plasma membrane overlying the principal segment and is removed from sperm during capacitation. The protein was purified for further characterization by anion exchange chromatography and gel filtration. In addition, six major proteins (30, 35, 38, 42, 52, and 66 kDa) which do not originate from accessory gland secretions were found to be strongly associated with the plasma membrane. Most of these proteins are not integral to the membrane and appear to develop an association with the plasma membrane during epididymal maturation. Similarly, calmodulin-binding proteins appear to develop strong associations with the plasma membrane during epididymal transit.