Detection of functional hydrogen-bonded water molecules with protonated/deprotonated key carboxyl side chains in the respiratory enzyme ba(3)-oxidoreductase

作者：Nicolaides Antonis; Soulimane Tewfik; Varotsis Constantinos^*

来源：Physical Chemistry Chemical Physics, 2015, 17(12): 8113-8119.

DOI：10.1039/c5cp00043b

The protonation/deprotonation of active carboxyl side chains by water networks forming the proton loading and exit sites in proteins are important steps in protein catalysis. An excellent system to study such basic principles is the heme-copper ba(3) from T. thermophilus because it utilizes one proton input channel and it delivers protons to the active site for both O-2 chemistry and proton pumping. We report the interaction of the heme a(3) Fe propionate-A and the Asp372-His376 pair which forms the valve for the exit pathway for the protons with internal water molecules in ba3 oxidoreductase by light minus dark FTIR spectroscopy in conjunction with H2O/(H2O)-O-18/D2O exchange. The proton loading site consists of several water molecules including w941/w946 which are H-bonded to propionate-A-H+, acting as the Zundel cation. The detection of two (H2O)-O-18 sensitive bands at 3640 and 3634 cm(-1) shows the existence of weakly H-bonded water molecules.

• 出版日期2015