Abstract
Although organisms from all kingdoms have either the system I or II cytochrome c biogenesis pathway, it has remained a mystery as to why these two distinct pathways have developed. We have previously shown evidence that the system I pathway has a higher affinity for haem than system II for cytochrome c biogenesis. Here, we show the mechanism by which the system I pathway can utilize haem at low levels. The mechanism involves an ATP-binding cassette (ABC) transporter that is required for release of the periplasmic haem chaperone CcmE to the last step of cytochrome c assembly. This ABC transporter is composed of the ABC subunit CcmA, and two membrane proteins, CcmB and CcmC. In the absence of CcmA or CcmB, holo(haem)CcmE binds to CcmC in a stable dead-end complex, indicating high affinity binding of haem to CcmC. Expression of CcmA and CcmB facilitates formation of the CcmA2B1C1 complex and ATP-dependent release of holoCcmE. We propose that the CcmA2B1C1 complex represents a new subgroup within the ABC transporter superfamily that functions to release a chaperone.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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ATP-Binding Cassette Transporters / genetics
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ATP-Binding Cassette Transporters / metabolism*
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Apoproteins / metabolism
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Bacterial Outer Membrane Proteins / genetics
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Bacterial Outer Membrane Proteins / metabolism*
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Bacterial Proteins / genetics
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Bacterial Proteins / metabolism
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Biological Transport
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Cytochrome c Group / biosynthesis*
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Escherichia coli / genetics
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Escherichia coli / metabolism
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Escherichia coli Proteins / genetics
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Escherichia coli Proteins / metabolism
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Heme / metabolism*
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Hemeproteins / biosynthesis
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Hemeproteins / genetics
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Hemeproteins / metabolism
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Models, Biological
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Molecular Chaperones / metabolism*
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Plasmids / genetics
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Recombinant Fusion Proteins / metabolism
Substances
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ATP-Binding Cassette Transporters
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Apoproteins
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Bacterial Outer Membrane Proteins
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Bacterial Proteins
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CcmA protein, bacteria
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CcmB protein, E coli
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CcmC protein, bacteria
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CcmE protein, E coli
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Cytochrome c Group
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Escherichia coli Proteins
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Hemeproteins
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Membrane Proteins
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Molecular Chaperones
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Recombinant Fusion Proteins
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Heme