CELL BIOLOGY: Perfect Packaging

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Science  17 Feb 2006:
Vol. 311, Issue 5763, pp. 919d-921d
DOI: 10.1126/science.311.5763.919d

Endothelial cells that line the blood vessels are packed with cigar-shaped organelles termed Weibel-Palade bodies. These secretory storage granules are filled with a protein known as von Willebrand's factor (VWF), which, when released from the cell, plays a key role in reestablishing the integrity of damaged blood vessels by recruiting platelets to the site of injury. Michaux et al. found that low pH within the storage granule is important to generate and maintain the tubular folding of the VWF, which in turn defines the morphology of the granule. Thus, the folding of VWF into tubules generates the unique architecture of the Weibel-Palade bodies.

The authors further sought to learn if this well-defined geometry has a functional significance beyond packaging and storage. They found that the tubular packaging is important during secretion to allow the VWF to unfold rapidly and efficiently into very long fibrils—up to 100 times the length of the packaged protein tubules—in order to trap circulating platelets. If folding is aberrant, or if a rise in granule pH interferes with packaging, VWF fails to unfold fully—presumably due to premature unraveling and tangling of the polypeptide before secretion—and platelet capture is severely compromised. — SMH

Dev. Cell 10, 223 (2006).

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