MetJ activation and SAM binding mode.

(A) Schematic representation of MetJ activation. Binding of SAM increases the DNA affinity of MetJ manifold. (B) Chemical structure of SAM (top) and SAH (bottom). The molecules mainly differ in the positive charge on the sulfur atom. (C) Fit of crystal structures of MetJ in apo (1CMC, green) and holo (1CMB, blue) form. The only major difference between the structures is the conformation of the loops underlayed in gray. These loops are in direct contact with other MetJ molecules in the crystal lattice, and thus their conformation is unlikely to represent the true in-vivo configuration. The bound co-repressor SAM is shown in red.