Fig. 5: Proposed mechanisms for 2,2’-bipyridine formation.

The PCP domain of CaeA2 is labeled in red. The C domains of CaeA3 and ColA3 are highlighted in green and blue, respectively. In contrast to favored routes b and c, unfavored route a is shown by gray color. Fl_ox oxidized flavin, Fl_red two-electron reduced flavin.