A burst of auxilin recruitment determines the onset of clathrin-coated vesicle uncoating
Department of Molecular and Cell Biology, Harvard University, Cambridge, Massachusetts, United StatesProceedings of the National Academy of Sciences (Impact Factor: 9.67). 08/2006; 103(27):10265-70. DOI: 10.1073/pnas.0603369103
Clathrin-coated pits assemble on a membrane and pinch off as coated vesicles. The released vesicles then rapidly lose their clathrin coats in a process mediated by the ATPase Hsc70, recruited by auxilin, a J-domain-containing cofactor. How is the uncoating process regulated? We find that during coat assembly small and variable amounts of auxilin are recruited transiently but that a much larger burst of association occurs after the peak of dynamin signal, during the transition between membrane constriction and vesicle budding. We show that the auxilin burst depends on domains of the protein likely to interact with lipid head groups. We conclude that the timing of auxilin recruitment determines the onset of uncoating. We propose that, when a diffusion barrier is established at the constricting neck of a fully formed coated pit and immediately after vesicle budding, accumulation of a specific lipid can recruit sufficient auxilin molecules to trigger uncoating.
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[Show abstract] [Hide abstract] ABSTRACT: Lipids are the most abundant organic compounds in the brain. The brain has a unique lipidome, and changes in lipid concentration, organization, and metabolism are associated with many neuronal diseases. Here, we discuss recent advances in understanding presynaptic membrane lipid organization, centered on illustrative examples of how the lipids themselves regulate membrane trafficking and control protein activity. This insight highlights that presynaptic terminals are membrane-remodeling machines and that cooperation between lipid and protein molecules underlies presynaptic activity.
- "In turn, the newly generated PtdIns(3,4)P2 recruits the PX-BAR domain protein Sorting nexin-9 and possibly other effectors to mature clathrincoated pits just prior to dynamin-mediated fission (Posor et al., 2013 ). Conversion of PtdIns(4,5)P2 into PtdIns(3,4)P2 by the successive action of Synaptojanin-1 (which forms PtdIns(4)P) and PI3K-C2-alpha (which uses PtdIns(4)P) might also contribute to clathrin coat removal given that the uncoating factor auxilin is recruited to membranes by PtdIns3P, PtdIns4P, or PtdIns(3,4)P2 (Massol et al., 2006 ). Moreover, these PtdInsP metabolizing enzymes modify the lipid composition of the vesicle membrane in a way that confers an ''endosome-like identity,'' which might allow fusion with an endosomal intermediate compartment (Jä hne et al., 2015). "
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- "Thus, auxilin functions as an adaptor that attracts Hsc70 to the clathrin coat. The precise regulation of irreversible uncoating by Hsc70 is unclear, but from life-cell imaging it has been inferred that coat disassembly is preceded in the cell by the budding of coated membranes [36,37]. The methods described above have now allowed us to test whether a spherical lattice is required for irreversible uncoating or if in principle clathrin-clathrin interactions could also be disrupted within planar arrangements by Hsc70. "