| Abstract
| - The cholesterol-binding protein NAP-22 is a major component of the detergent-insoluble low-density fraction of rat brain. In this study, we found, using fluorescence microscopy, that native NAP-22,but not a demyristoylated form, binds to cholesterol-rich raft-like domains in planar-supported monolayersand remains bound after nonionic detergent extraction. NAP-22 also protects the cholesterol-rich domainsduring extraction by methyl-β-cyclodextrin. The lateral mobility of this protein is much lower than thatof other raft components in model membranes, suggesting that both cholesterol binding and inter-NAP-22 interactions markedly reduce its lateral diffusion. This study suggests that NAP-22 binding may beemployed to image cholesterol-rich regions, such as caveolae/rafts, on the plasma membrane of cells, andpreliminary efforts in that direction are presented.
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