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Nature. 2017 Dec 21;552(7685):410-414. doi: 10.1038/nature25146. Epub 2017 Dec 13.

Dynamics of phosphoinositide conversion in clathrin-mediated endocytic traffic.

Author information

1
Department of Cell Biology, Harvard Medical School, 200 Longwood Ave, Boston, Massachusetts 02115, USA.
2
Program in Cellular and Molecular Medicine, Boston Children's Hospital, 200 Longwood Ave, Boston, Massachusetts 02115, USA.
3
Department of Pediatrics, Harvard Medical School, 200 Longwood Ave, Boston, Massachusetts 02115, USA.
4
Physics of Living Systems Group, Massachusetts Institute of Technology, 400 Technology Square, Cambridge, Massachusetts 02139, USA.

Abstract

Vesicular carriers transport proteins and lipids from one organelle to another, recognizing specific identifiers for the donor and acceptor membranes. Two important identifiers are phosphoinositides and GTP-bound GTPases, which provide well-defined but mutable labels. Phosphatidylinositol and its phosphorylated derivatives are present on the cytosolic faces of most cellular membranes. Reversible phosphorylation of its headgroup produces seven distinct phosphoinositides. In endocytic traffic, phosphatidylinositol-4,5-biphosphate marks the plasma membrane, and phosphatidylinositol-3-phosphate and phosphatidylinositol-4-phosphate mark distinct endosomal compartments. It is unknown what sequence of changes in lipid content confers on the vesicles their distinct identity at each intermediate step. Here we describe 'coincidence-detecting' sensors that selectively report the phosphoinositide composition of clathrin-associated structures, and the use of these sensors to follow the dynamics of phosphoinositide conversion during endocytosis. The membrane of an assembling coated pit, in equilibrium with the surrounding plasma membrane, contains phosphatidylinositol-4,5-biphosphate and a smaller amount of phosphatidylinositol-4-phosphate. Closure of the vesicle interrupts free exchange with the plasma membrane. A substantial burst of phosphatidylinositol-4-phosphate immediately after budding coincides with a burst of phosphatidylinositol-3-phosphate, distinct from any later encounter with the phosphatidylinositol-3-phosphate pool in early endosomes; phosphatidylinositol-3,4-biphosphate and the GTPase Rab5 then appear and remain as the uncoating vesicles mature into Rab5-positive endocytic intermediates. Our observations show that a cascade of molecular conversions, made possible by the separation of a vesicle from its parent membrane, can label membrane-traffic intermediates and determine their destinations.

PMID:
29236694
PMCID:
PMC6263037
DOI:
10.1038/nature25146
[Indexed for MEDLINE]
Free PMC Article

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