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| Environmental
Bioinorganic Chemistry |
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Life
on CO and CO2
Phototrophic
anaerobes such as Rhodospirillum rubrum have the ability
to utilize the gaseous pollutant CO as their sole carbon and
energy source. This ability derives from the oxidation of
CO to CO2
catalyzed at the Ni-Fe-S (C-clusters) of the enzyme carbon
monoxide dehydrogenase (CODH). Alternatively, acetogens such
as Moorella thermoacetica use bifunctional CODH/acetyl-CoA
synthases (ACSs) and metallocenters known as A-clusters to
convert the greenhouse gas CO2 to acetyl-CoA.
Analogous CODH/ACSs in methanogens also catalyze the degradation
of acetyl-CoA, which ultimately forms another greenhouse gas,
methane. |
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R. rubrum CODH |
M. thermoacetica CODH/ACS |
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Collectively,
CODH/ACSs play a major role in the global carbon cycle as
well as in the formation and removal of greenhouse gases and
CO in our environment. It has been estimated that 1
x 108 tons of CO are removed by bacteria from the
lower atmosphere and earth annually. A better understanding
of the CODH mechanism could
lead to the development of biomimetic catalysts capable of
lowering the concentration of CO in heavily polluted areas. |
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Publications
Drennan, C.L., Heo, J., Sintchak, M.D., Schreiter, E., Ludden,
P.W. (2001) Life on Carbon Monoxide: X-ray Structure
of Rhodospirillum rubrum Ni-Fe-S Carbon Monoxide Dehydrogenase,
Proceedings of the National Academy of Sciences U.S.A.
98:11973–11978.
Doukov,
T.I., Iverson, T.M., Seravalli, J., Ragsdale, S.W., and Drennan,
C.L. (2002) A
Ni-Fe-Cu Center in a Bifunctional Carbon Monoxide Dehydrogenase/Acetyl-CoA
Synthase, Science 298:567–572.
Drennan,
C.L. and Peters, J. W. (2003) Surprising Cofactors
in Metalloenzymes, Current Opinion in Structural
Biology. 13:220–226.
Drennan,
C.L., Doukov, T.I., and Ragsdale, S.W. (2004) The
Metalloclusters of Carbon Monoxide Dehydrogenase/Acetyl-CoA
Synthase: A Story in Pictures, Journal of Biological
Inorganic Chemistry. 9:511-515.
Doukov,
T.I., Blasiak, L.C., Seravalli, J., Ragsdale, S.W., Drennan,
C.L. (2008) Xenon
in and at the End of the Tunnel of Bifunctional Carbon Monoxide
Dehydrogenase/Acetyl-CoA Synthase, Biochemistry.
47(11):3474-3483.
Kung,
Y., Doukov, T.I., Seravalli, J., Ragsdale, S.W., Drennan,
C.L. (2009) Crystallographic
Snapshots of Cyanide- and Water-Bound C-Clusters from Bifunctional
Carbon Monoxide Dehydrogenase/Acetyl-CoA Synthase.
Biochemistry. 48(31):7432-7440.
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Pathway
of CO2 Fixation
One
molecule of CO2 (blue, top right) is converted
to formate, then completely reduced to a methyl moiety in
a series of steps that are catalyzed by folate dependent enzymes.
This methyl moiety is transferred by a methyltranferase (MeTr)
to the corrinoid-iron-sulfur protein (CFeSP). In turn, CFeSP
transfers the methyl group to the ACS subunit of bifunctional
CODH/ACS. The other molecule of CO2 (red, top right)
is reduced to CO by the C-cluster of the CODH subunit of CODH/ACS.
The CO intermediate is then transferred to the A-cluster of
the ACS subunit through a long channel in the enzyme. Finally,
the methyl group, CO, and CoA are assembled to form acetyl-CoA.
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