Spatial distribution and functional significance of activated vinculin in living cells.

Conformational change is believed to be important to vinculin's function at sites of cell adhesion. However, nothing is known about vinculin's conformation in living cells. Using a Forster resonance energy transfer probe that reports on changes in vinculin's conformation, we find that vinculin is in the actin-binding conformation in a peripheral band of adhesive puncta in spreading cells. However, in fully spread cells with established polarity, vinculin's conformation is variable at focal adhesions. Time-lapse imaging reveals a gradient of conformational change that precedes loss of vinculin from focal adhesions in retracting regions. At stable or protruding regions, recruitment of vinculin is not necessarily coupled to the actin-binding conformation. However, a different measure of vinculin conformation, the recruitment of vinexin beta by activated vinculin, shows that autoinhibition of endogenous vinculin is relaxed at focal adhesions. Beyond providing direct evidence that vinculin is activated at focal adhesions, this study shows that the specific functional conformation correlates with regional cellular dynamics.