Teeny tiny rafts

杨柳

Mayor/Elsevier
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/ s3 \. ]" Q8 @; h' gTiny but dynamic domains define the elusive lipid raft, based on results from Madan Rao, Satyajit Mayor (National Centre for Biological Science, Bangalore, India), and colleagues.; R+ K3 E1 E8 b( y' W' F

$ f* a4 }  ?$ |6 G  VDescribing the structure and components of rafts〞membrane domains enriched in specific lipids and proteins〞has been a long-standing challenge for cell biologists. In this new report, the authors use FRET, photobleaching, and theoretical modeling to get the closest look yet at raft components called GPI-APs (GPI-anchored proteins). They show that lipid rafts contain small clusters (four or fewer molecules) of very tight-knit GPI-APs packed into an 4-nm-wide space.: R. b7 ~9 T7 p+ g* R4 q9 \( {
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About a third of any given GPI-AP species is found in rafts. The rest remain as monomers. This percentage holds true across multiple expression levels, which is inconsistent with equilibrium-based formation. "It means rafts have to be actively maintained," says Mayor. "And within these regions, the GPI proteins form clusters."4 |) V+ H+ l* R+ p" K0 B! D
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Different types of GPI-APs are found within a cluster, and the clusters are dynamic〞cross-linking of one species removes it from the cluster, and another species readily takes its place. The cross-linked GPI-APs formed larger groups that were endocytosed by the clathrin-mediated pathway, rather than the route responsible for uptake of raft GPI-APs. Thus, ligation of a receptor could change its fate by altering its lipid environment.
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Sharma, P., et al. 2004. Cell. 116:577–589.(Native clusters (black circles) reorgani)