Figure 2. Composite omit electron density confirms that loop 2 is ordered in our E. coli class Ia RNR structures.

Protein is shown as grey ribbons with substrate, loop 2, and specificity effector in sticks and labeled. Carbon is colored in yellow, oxygen in red, nitrogen in blue, phosphorus in orange. 2F_o−F_c composite omit density is shown contoured at +1.0 σ (green mesh). (A) α₄β₄-CDP/dATP structure. (B) α₄β₄-UDP/dATP structure. (C) α₄β₄-ADP/dGTP structure. (D) α₄β₄-GDP/TTP structure.

DOI: http://dx.doi.org/10.7554/eLife.07141.005