Abstract
Consideration of a long record of research, including recent results, on the behavior and influences of cholesterol in the membranes of mammalian cells focuses attention on a new model for the required roles of cholesterol in mammalian cell biology. Most cellular cholesterol is found in the plasma membrane of mammalian cells. Cholesterol decreases membrane permeability through an ordering of the lipid hydrocarbon chains. Membrane cholesterol modulates the activity of integral membrane enzymes. Stimulation of membrane protein activity likely occurs through structurally specific sterol–protein binding, stabilizing the active conformation of the protein. Inhibition of membrane enzyme activity can occur through an analogous mechanism. Inhibition can also be promoted by a cholesterol-driven reduction in free volume within the bilayer, inhibiting protein conformational changes necessary for protein function. The same model can be applied to understand the essential roles of ergosterol in yeast and of plant sterols in plants. While mammalian cells specifically require cholesterol, yeast specifically requires ergosterol, and plants specifically require plant sterols for growth.
Published Version
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