VWF springs into action

Following blood vessel injury, long strings of multimeric von Willebrand's factor (VWF) act as a scaffold for platelets to help staunch bleeding. The VWF strings, 100-μm long or more, may be stored as a coiled, tubular spring inside obligately extended organelles, suggest Grégoire Michaux, Daniel Cutler (University College London, UK), and colleagues.

These organelles are the 1–5 μm-long Weibel-Palade bodies (WPBs). “If you look down a microscope they are such striking organelles—long and just very pretty,” says Cutler. “There had to be something underlying this.”

Cutler's answer was striking. “The shape is determined by the function of the protein after exocytosis,” he says. The organelle needs to be long, he suggests, so that the spring can be stored in a straight line, allowing easy expansion upon release. “If it is coiled [inside the cell],”...