 The active site for the enzyme occurs at the interface between the two domains.Binding of the enzyme to the thylakoid membrane involves a polyproline type II helix created between two FNR monomers and several proline rich integral membrane proteins.As of late 2007, 54 structures had been solved for this class of enzymes, with PDB accession codes , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , and .