Hydrogen bond network in the active site of rkbPAP. The hydrogen bond pattern demonstrates how the initial, pre-catalytic enzyme-substrate complex may be stabilized. The protonation state of sulfate at the pH of crystallization (pH 4.0) is SO42-. Residue His295 (indicated by a "*") is the only amino acid that is not invariant among PAPs from different sources.
Schenk et al. BMC Structural Biology 2008 8:6 doi:10.1186/1472-6807-8-6