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Fig. 1. Raft clustering and domain-induced budding. Before clustering, proteins associate with rafts (grey) to various extents. A GPI-anchored protein (gold) resides exclusively in rafts, a doubly acylated protein (red) is mainly in rafts, a transmembrane protein (green) is mainly outside rafts, and another transmembrane protein (pink) is excluded from rafts (A). Clustering is induced, for example, by the binding of a multimeric protein of the annexin type (blue) to the cytoplasmic face of rafts. The strongly raft-associated GPI-anchored and doubly acylated proteins partition into clustered rafts. The weakly raft-associated transmembrane protein is driven into clustered rafts by crosslinking with a divalent interaction partner, e.g. a lectin (black). Note that the recruitment of the weakly raft-associated transmembrane protein is not complete, nor are all rafts clustered. For simplicity, only one type of raft cluster is shown, i.e. differential clustering of rafts into separate domains with different constituents is not depicted (B). Growth of the clustered raft domain beyond a critical size induces budding (C). Finally, a transport container consisting of raft components pinches off from the parent membrane by fission at the domain boundaries (D).
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