Figure 5. An illustrations of the Lac repressor in its possible conformations.

A space filling model of the Lac repressor tetramer in its stiff V-shaped conformation (right) and a schematic representation of our assumed model of the open (extended) conformation of the Lac repressor (left). To simulate the open conformation, we assumed that the two dimeric arms of the Lac repressor are connected by a spherical joint that permits them to rotated freely about the joint. Thus, the three degrees of freedom characterizing the relative orientation between the two arms can attain any feasible value in the configurational space with no energetic cost for the conformational change of the Lac repressor.