D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
Lecture 12: Vesicle formation and fusion
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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Protein sorting in the cytosol - summary
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Vesicular transport
Questions to consider: How is cargo selected? How is cargo separated from resident proteins of the donor organelle? How do vesicles fuse? How is a vesicle targeted to fuse with a particular organelle?
or in the cytosol
Prerequisite for fusion: Vesicle uncoating
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
The recruitment of a small GTPase to the donor membrane is the first step of vesicle formation. The main function of the coat is the selective recruitment of cargo into the budding vesicleciation after fusion requires ATP hydrolysis
• NSF is an ATPase that uses ATP hydrolysis to dissolve the tight interaction between the SNAREs. • SNAREs are recycled for a new round of transport.
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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How are vesicles formed?
Coat and cargo recruitment
vesicle buds off
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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Vesicle fusion is mediated by SNARE pair formation
A SNARE pair contains 4 coiled-coiled domains - one: SNARE on vesicle - one: SNARE on target membrane - two: either additional SNAREs on target membrane
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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A link between coat components and disease
• General defects in protein secretion cell death Protein secretion is an essential process
• Mutations that only block the secretion of specific proteins Sec23A: linked to a rare cranofacial disorder that causes skeletal disorders Sec24B: defects in neural tube closure because a receptor required for the development of the neural epithelium is not trafficked properly (Merte et al., 2010)
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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The mechanism of vesicle formation is conserved
Lee et al., 2004
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.
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Vesicles look similar by electron microscopy
D103 W2011 Cell Biology - lecture 12- copyright © Suetterlin and MacGregor - all rights reserved.