The membrane anchors of the heme chaperone CcmE and the periplasmic thioredoxin CcmG are functionally important.
The cytochrome c maturation system of Escherichia coli contains two monotopic membrane proteins with periplasmic, functional domains, the heme chaperone CcmE and the thioredoxin CcmG. We show in a domain swap experiment that the membrane anchors of these proteins can be exchanged without drastic loss of function in cytochrome c maturation. By contrast, the soluble periplasmic forms produced with a cleavable OmpA signal sequence have low biological activity. Both the chimerical CcmE (CcmG'-'E) and the soluble periplasmic CcmE produce low levels of holo-CcmE and thus are impaired in their heme receiving capacity. Also, both forms of CcmE can be co-precipitated with CcmC, thus restricting the site of interaction of CcmE with CcmC to the C-terminal periplasmic domain. However, the low level of holo-CcmE formed in the chimera is transferred efficiently to cytochrome c, indicating that heme delivery from CcmE does not involve the membrane anchor.
Ahuja
Umesh
U
Institut für Mikrobiologie, Eidgenössische Technische Hochschule, Wolfgang-Pauli-Str. 10, CH-8093 Zürich, Switzerland. ahuja@micro.biol.ethz.ch
Thöny-Meyer
Linda
L
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport / Q000235:genetics; D045304:Cytochromes c / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D006418:Heme / Q000235:genetics / Q000378:metabolism; D006420:Hemeproteins / Q000235:genetics / Q000378:metabolism*; D019897:Periplasm / Q000201:enzymology* / Q000235:genetics; D011490:Protein Disulfide Reductase (Glutathione) / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism
D001425:Bacterial Outer Membrane Proteins; C115384:CcmE protein, E coli; D029968:Escherichia coli Proteins; D006420:Hemeproteins; D011993:Recombinant Fusion Proteins; C078167:OMPA outer membrane proteins; D006418:Heme; D013879:Thioredoxins; D045304:Cytochromes c; C485980:Ccmg protein, E coli; D011490:Protein Disulfide Reductase (Glutathione)