A conserved haem redox and trafficking pathway for cofactor attachment.
A pathway for cytochrome c maturation (Ccm) in bacteria, archaea and eukaryotes (mitochondria) requires the genes encoding eight membrane proteins (CcmABCDEFGH). The CcmABCDE proteins are proposed to traffic haem to the cytochrome c synthetase (CcmF/H) for covalent attachment to cytochrome c by unknown mechanisms. For the first time, we purify pathway complexes with trapped haem to elucidate the molecular mechanisms of haem binding, trafficking and redox control. We discovered an early step in trafficking that involves oxidation of haem (to Fe(3+)), yet the final attachment requires reduced haem (Fe(2+)). Surprisingly, CcmF is a cytochrome b with a haem never before realized, and in vitro, CcmF functions as a quinol:haem oxidoreductase. Thus, this ancient pathway has conserved and orchestrated mechanisms for trafficking, storing and reducing haem, which assure its use for cytochrome c synthesis even in limiting haem (iron) environments and reducing haem in oxidizing environments.
Richard-Fogal
Cynthia L
CL
Department of Biology, Washington University, St Louis, MO 63130, USA.
Frawley
Elaine R
ER
Bonner
Eric R
ER
Zhu
Huifen
H
San Francisco
Brian
B
Kranz
Robert G
RG
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D045304:Cytochromes c / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006418:Heme / Q000302:isolation & purification / Q000378:metabolism*; D006420:Hemeproteins / Q000302:isolation & purification / Q000378:metabolism*; D006873:Hydroquinones / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008190:Lyases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D011485:Protein Binding
D001425:Bacterial Outer Membrane Proteins; C451399:CcmH protein, E coli; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D006873:Hydroquinones; D006418:Heme; D045304:Cytochromes c; D007501:Iron; D008190:Lyases; C031581:cytochrome C synthetase