FIGURE 1.

Structure of cNOR from P. aeruginosa (Protein Data Bank code 3O0R) (13) with the predicted proton transfer pathways. The NorB (light gray, transparent) and NorC (black, transparent in B–D) subunits are shown in a helical representation. A, the residues that are predicted to be involved in proton transfer are indicated with sticks, in cyan (pathway 1), magenta (pathway 2), or wheat (pathway 3). The location of the K-pathway (not present in cNOR but important in other HCuOs) is indicated in dark red. B–D, close-up of the proton transfer pathways. The blue arrows indicate the point of entrance for waters from the bulk. The predicted proton transfer pathways are indicated with stick representations in cyan (pathway 1; A), in magenta (pathway 2; B), or wheat (pathway 3; C). The corresponding residues in P. denitrificans cNOR are indicated in parenthesis in case they are different or if they were exchanged in this study. Residues in NorC are indicated with a C in superscript. This figure was prepared with PyMOL (Schrödinger, LLC, New York).