Inactivation of Cytochrome o Ubiquinol Oxidase Relieves Catabolic ...
Exploring the Structure and Function of Cytochrome bo 3 Ubiquinol Oxidase from Escherichia coli
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Transcript of Exploring the Structure and Function of Cytochrome bo 3 Ubiquinol Oxidase from Escherichia coli
Exploring the Structure and Function of Cytochrome bo3 Ubiquinol Oxidase from
Escherichia coli
Lai Lai Yap
Department of Biochemistry
Heme-Copper Oxidase Superfamily
• catalyze reduction of oxygen to water, and utilizes free energy produced to pump protons across membrane
• transmembrane proton and voltage gradient thus generated is converted to useful energy forms (eg. ATP by ATP synthase)
• 2 main groups (based on electron-donating substrate) : cytochrome c oxidase (eg. mitochondrial cytochrome c oxidase) and ubiquinol oxidase (eg. cytochrome bo3 ubiquinol oxidase)
• membership based on presence of subunit homologous to subunit I of mammalian cytochrome c oxidase
• subunit I:
– largest subunit
– binuclear center (where O2 binds and is reduced to water) consisting of a heme and copper (CuB)
– a second heme (which facilitates transfer of electrons to binuclear center)
Heme-Copper Oxidase Superfamily
Respiratory Chains of E. coli
High O2 affinity
Low O2 affinitySubstrates eg. NADH, succinate
Dehydrogenases
Quinone
Cytochrome bo3
Cytochrome bd
O2
O2
Cytochrome bo3 ubiquinol oxidase
• a terminal oxidase in the aerobic respiratory chain of Escherichia coli
• member of the heme-copper oxidase superfamily
• consists of four subunits
• catalyzes two-electron oxidation of ubiquinol-8 (Q8H2) at periplasmic side of cytoplasmic membrane and four-electron reduction of oxygen to water at cytoplasmic side
• also functions as a proton pump by translocating protons across the cytoplasmic membrane to establish an electrochemical proton gradient
• possible mechanism: ubiquinone bound at the high affinity site (QH) acts as cofactor and mediates electron transfer from ubiquinol substrate (at the low-affinity QL site) to heme b
• reduced heme b then provides electrons to the binuclear center for the reduction of oxygen to water
Electron and proton transfer in cytochrome bo3 ubiquinol oxidase
QL
QH
II IIII IV
½ O2 + 2H+H2O 2H+
translocation
2H+
2e-2e-
2e-
2e-
periplasm
cytoplasm
Heme b
Heme o3
CuB
QH2
Subunit ISubunit IISubunit IIISubunit IV
P
C
ubiquinol binding site
Spherical rendering structure of ubiquinol oxidase
P
C
ubiquinol binding site
Subunit ISubunit IISubunit IIISubunit IV
Structure of ubiquinol oxidase
Heme b Heme o3
CuB
His106
His421
His334
His333
His284
His419
Redox metal centers of ubiquinol oxidase (in subunit I)
Rainbow rendering of ubiquinol oxidase and cytochrome c oxidase
Cytochrome c oxidase Ubiquinol oxidase
Cytochrome c binding site Ubiquinol binding site
Superposition of ubiquinol oxidase and cytochrome c oxidase
Ubiquinol oxidase
Cytochrome c oxidase
Proton transfer pathways
• D- and K-channels in subunit I
• channels form polar cavities that originate on the cytoplasmic side, leading to the binuclear center for proton pumping and water formation
• D-channel : uptake of both chemical and pumped protons
• K-channel : load enzyme with protons at some earlier catalytic steps
D- and K-channels of ubiquinol oxidase
D-channel K-channelD-channel K-channel
D135T211
N142
N124
S145
T204
T149
T201
E286
H106
H421
H333
H334
H284
Y288
T359
K362
S315S299
H+ out
QL
QH
II IIII IV
½ O2 + 2H+H2O 2H+
translocation
2H+
2e-2e-
2e-
2e-
periplasm
cytoplasm
Heme b
Heme o3
CuB
QH2
P
C
ubiquinol binding site
Subunit ISubunit IISubunit IIISubunit IV
Structure of ubiquinol oxidase
Ubiquinol oxidase with modeled ubiquinone (at ubiquinol binding site)
ubiquinone
L160
R71
D75
M78
M79I102
H98
Q101
Ubiquinone binding site of ubiquinol oxidase with modeled ubiquinone
Electron and proton transfer in cytochrome bo3 ubiquinol oxidase
QL
QH
II IIII IV
½ O2 + 2H+H2O 2H+
translocation
2H+
2e-2e-
2e-
2e-
periplasm
cytoplasm
Heme b
Heme o3
CuB
QH2
ubiquinone
heme b
heme o3
CuB
M79I102
H106
H421
H419
Membrane normal view of subunit I with modeled ubiquinone
possible electron path from ubiquinone to binuclear center