Figure 1: Phospholipids direct membrane sorting. | Nature

Figure 1: Phospholipids direct membrane sorting.

From: Lipid code for membrane recycling

Figure 1

The proteins epidermal growth factor receptor (EGFR) and transferrin receptor (TfR) are removed from the cell surface in membranous structures called endosomes. The membranes of early endosomes contain PI3P (PI3P-containing membranes are indicated in blue) — a phospholipid of the phosphoinositide family that is tagged with a phosphate group at 'position 3'. As they mature, endosomes are sorted to determine the fate of the proteins they contain. In membrane regions such as those harbouring EGFR, PI3P is converted to PI(3,5)P2 (yellow membranes), marking the region for degradation (the lipids present in the outer membrane of endosomes destined for degradation remain unknown). Ketel et al.1 report that regions destined for recycling, such as those harbouring TfR, are modified by the sequential action of two enzymes. First, MTM1 removes the phosphate group from PI3P, then PI4K2A adds a phosphate group to position 4, generating PI4P (red membranes). The presence of PI4P directs the endosome back to the plasma membrane so that the proteins can be reused.

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