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- Phospholipid scramblase, a membrane-associated protein, literally “scrambles” lipids within the lipid bilayer of a sperm cell. This activity occurs in response to cAMP-dependent PKA signaling pathway initiation.
- The scrambling of lipids is manifested through moving them between outer and inner leaflets, causing asymmetry as seen in the model image at left.
- This movement is evidenced by phosphatidylserine and phsophatidylethanolamine appearing in outer leaflet after scramblase activity, whereas they were present only in the inner leaflet prior to capacitation.
- The movement of lipids includes redistribution of cholesterol within the membrane structure, reducing membrane stability. Researchers tout this decreased stability as the reason cholesterol efflux is able to occur.
- In Flesch’s group’s research, they utilized M540 fluorescence markers to label bicarbonate-mediated scrambling of phospholipids.
- The results were separated into high and low fluorescence groups.
- A significant difference in cholesterol levels existed between the two groups.
- High membrane fluidity, suggesting capacitation, was associated with low amounts of cholesterol.
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| This image is used with permission from senior author of: Flesch FM, Brouwers JFHM, Nievelstein PFEM, Verkleij AJ, van Golde LMG, Colenbrander B, Gadella BM. 2001. Bicarbonate stimulated phospholipid scrambling induces cholesterol redistribution and enables cholesterol depletion in the sperm plasma membrane. Journal of Cell Science 114(19):3543-55. |
