Electron microscopy of rotary shadowed vinculin and vinculin complexes.

Chicken gizzard smooth muscle vinculin, purified according to the method of Feramisco & Burridge (1980), was examined by rotary shadowing and electron microscopy. Individual vinculin molecules have two domains: a globular head with a diameter of 8.0 nm, and a tail 20 nm long. In high salt, vinculin self-associates into multimers containing two to six individual molecules. These molecules associate head to head and tail to tail, but the tail to tail association appears to be favored. Electron microscopy of the approximately 100,000 Mr major fragment of vinculin was performed. The tail region appeared to be cleaved off, making the head region less compact.

A structural comparison of tryptic fragments of three types of intermediate filaments.

We have compared tryptic fragments of three types of intermediate filaments, emphasizing structural characteristics as seen in the electron microscope. Variable, long alpha-helical rod fragments were found to be similar for keratin, neurofilaments and desmin filaments. Short rod fragments from keratin and neurofilaments appeared similar when observed by electron microscopy. Short rod fragments were not seen in desmin filament digests. In addition to these elongated particles, globular fragments, which have not been described previously, were obtained from all three types of intermediate filaments. These globular fragments were characterized by gel filtration and electron microscopy, and compared to globular proteins of known size using both methods. The diameter was about 6 nm and the molecular weight was estimated to be 50 000-60 000. These globular particles may comprise the short, nonhelical regions from several IF protein subunits, which are clustered into an interface in the intact filament or protofilaments.