Molecular shape of vinculin in aqueous solution.

We have investigated the molecular structure of chicken gizzard vinculin in solution. The translational diffusion coefficient of the intact protein and its amino-terminal head fragment, as obtained by proteolytic digestion, was determined by photon correlation spectroscopy. The experimental data are compared with hydrodynamic calculations, where the anisotropic shape of the macromolecule is modeled by spherical subunits. Our results are in agreement with the concept of a "balloon on a string" for the molecular shape of native vinculin. The existence of dimer and oligomer structures in low ionic strength buffer can be excluded. The calculated dimensions of the head fragment were estimated to r = 3.3 nm for a spherical particle, but the diffusion coefficient suggests a slightly anisotropic shape. In solution, the rod-like tail exhibits some flexibility, which is probably located in the "neck region" of the protein, considering the known sequence data.