Next, we considered that the m-shaped loop of one subunit and the N-finger of the adjacent subunit interact via hydrogen bonds: i.e. GLU166 and PHE140 of one subunit, and SER1 of the other. Such hydrogen bonds are only preserved in the fully symmetric double occupied enzyme (symmetric space group) while it breaks for both subunits in the asymmetric space groups (P212121), either single or double occupied. These results suggest that symmetry might impact the stability of such interaction and, in turn, of the 'active' geometry (Fig. ). However, such observation should be taken with care, since the highly flexible structure of the N-term, plus the presence of artificial capping (see Methods) might impact significantly on its dynamic behavior.