Isolation and characterization of mammalian villin and fimbrin, the two bundling proteins of the intestinal microvilli.

Using a Mg2+ rather than the standard Ca2+ precipitation method microvillus membrane vesicles of porcine intestinal epithelial cells with a relatively well preserved cytoskeleton are obtained. Such vesicles are long and relatively straight and retain some of the core filament structure typical of non-vesicularized microvilli. They are therefore a good starting material for the purification of mammalian F-actin bundling proteins. We have purified the two previously predicted bundling proteins villin and fimbrin from such preparations and show that in most but not all aspects they resemble their counterparts in chicken microvilli. The now documented F-actin severing activity of purified porcine villin explains the easy vesicularization of porcine microvilli in the traditional Ca2+ precipitation method.