Study of the Proton Pumping Mechanism of the Aa3-Type Cytochrome C Oxidase

138 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009.Cytochrome c oxidase is the last component of the respiratory chains. It accepts electrons from a water-soluble or membrane-anchored cytochrome c and catalyzes the reduction of O2 to water (O2 + 4e- + 4H+ → 2 H2O). In cytochrome aa3 oxidase (C cO), electrons from cytochrome c are first transferred to a copper center, CuA, which is located on the electrically positive (P) side of the membrane, then transferred through low spin heme a to a binuclear center (high spin heme a3 and CuB) which is the catalytic site of the CcOs. O2 binds to reduced heme a3, which is followed by stepwise reduction, requiring four protons and four electrons. These four protons are taken up from the negative (N) side of the membrane through two proton conductive channels (D-channel and K-channel). C cO is also a redox-driven proton pump, i.e., the free energy produced by O2-reduction reaction is coupled to the pumping of four other protons through the proton conductive channel (D-channel) across the membrane. The proton gradient across the membrane can be utilized for other biological activities, for example, ATP synthesis. The molecular mechanism of proton pumping is not well understood.This thesis focuses on proton pumping mechanism of CcO. A series of mutants of the key D-channel residues N121, N139, N207 and S142 are made and characterized. Some of the mutants demonstrate decoupling feature, i.e., they retain high O2-reduction activities but lose the abilities to pump protons. Crystallographic study on N139C and N139D suggests that the water molecules in the D-channel undergo conformational change and the hydrogen bonding network of water molecules are disturbed. This may delay the proton transportation through the D-channel and abolish proton pumping.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD