Fig. 5.

Proposed proton-relay path. (A) The hydrogen bond network bridging the Tyr193 ηO and a solvent water molecule within the SyLPOR and TeLPOR structures. The well-positioned water, shown in the red sphere, is fixed by the backbone oxygens of Ala91 and Asn115, and the ε-amino group of Lys197. The hydrogen bonds are shown in dashed lines and the bond lengths (Å) are in blue for SyLPOR and dark green for TeLPOR. (B) A proposed proton-relay path following the hydride transfer from NADPH to C17. The photon energy (hv) is represented by a yellow thunderbolt.