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Published on: March 4, 2013
Arrangement of PMCA4 in bovine sperm membrane fractions
H Post1, A Schwarz, T Brandenburger
1Department of Anatomy and Cell Biology, Philipps University of Marburg, Marburg, Germany. posth@staff.uni-marburg.de
Abstract:
The plasma membrane Ca(2+) -ATPase (PMCA) is the main restorer of Ca(2+) balance in sperm. Particularly, PMCA isoform 4 has an essential function in sperm fertility by its participation in gaining sperm hypermotility. PMCA activity is influenced by its lipid environment. Sperm membranes exhibit lipid raft microdomains or detergent-resistant membrane domains, enriched in sphingolipids and cholesterol, forming functional specialized areas. Lipid and protein composition of lipid rafts alters during the capacitation process, which is characterized by a cholesterol efflux. In this study, the localization of PMCA4 in lipid membrane fractions of the sperm plasma membrane was investigated. We identified PMCA4 in both the detergent-resistant membrane (DRM) and in the detergent-soluble (DS) fraction of caput and cauda sperm, respectively. Capacitation did not influence PMCA4 localization. In immunocytochemical studies PMCA4 was co-localized with the lipid raft/DRM marker caveolin in the mid piece of caput and cauda sperm. Functional studies with seminal vesicle major protein PDC-109 showed that the Ca(2+) -ATPase activity in DS fractions of cauda sperm and capacitated cauda sperm was stronger enhanced than in the DRMs. In both fractions the effect was statistically significant. In contrast, in lipid overlay experiments PDC-109 interacted stronger with the lipids extracted from DRMs than with lipids extracted from DS. Our results indicate a possible functional compartmentalization of PMCA in bull sperm membranes and point to a presumptive, yet unknown interaction partner of Ca(2+) -ATPase and PDC-109, mediating the PDC-109 action from DRMs to the DS fraction of sperm plasma membrane.
Insights
The plasma membrane Ca(2+)-ATPase (PMCA) in bull sperm is located in lipid rafts and soluble membrane fractions. Its activity is influenced by seminal vesicle protein PDC-109, suggesting compartmentalization for sperm function.
Area of Science:
- Sperm biology
- Membrane biophysics
- Biochemistry
Background:
- The plasma membrane Ca(2+)-ATPase (PMCA) regulates calcium homeostasis in sperm.
- PMCA isoform 4 is crucial for sperm hypermotility and fertility.
- Sperm membranes contain lipid rafts, specialized domains affecting protein function.
Purpose of the Study:
- To investigate the localization of PMCA4 within bull sperm membrane lipid fractions.
- To explore the influence of capacitation on PMCA4 localization.
- To examine the interaction of seminal vesicle protein PDC-109 with PMCA4 in different membrane fractions.
Main Methods:
- Fractionation of sperm plasma membranes into detergent-resistant (DRM) and detergent-soluble (DS) components.
- Immunocytochemical localization of PMCA4 and caveolin.
- In vitro functional assays measuring Ca(2+)-ATPase activity.
- Lipid overlay experiments to assess protein-lipid interactions.
Main Results:
- PMCA4 was identified in both DRM and DS fractions of caput and cauda sperm.
- Capacitation did not alter PMCA4 localization.
- PMCA4 co-localized with the lipid raft marker caveolin.
- PDC-109 significantly enhanced Ca(2+)-ATPase activity in DS fractions compared to DRMs.
- PDC-109 showed stronger interaction with lipids from DRMs than DS fractions.
Conclusions:
- PMCA4 exhibits functional compartmentalization within bull sperm membranes.
- A potential interaction partner mediates PDC-109's effect on PMCA4 from DRMs to the DS fraction.
- These findings offer insights into the regulation of sperm function and fertility.
