Ornithine lipid is required for optimal steady-state amounts of c-type cytochromes in Rhodobacter capsulatus.
The c-type cytochromes are haemoproteins that are subunits or physiological partners of electron transport chain components, like the cytochrome bc(1) complex or the cbb(3)-type cytochrome c oxidase. Their haem moieties are covalently attached to the corresponding apocytochromes via a complex post-translational maturation process. During our studies of cytochrome biogenesis, we uncovered a novel class of mutants that are unable to produce ornithine lipid and that lack several c-type cytochromes. Molecular analyses of these mutants led us to the ornithine lipid biosynthesis genes of Rhodobacter capsulatus. Herein, we have characterized these mutants, and established the chemical structure of this non-phosphorus membrane lipid from R. capsulatus. Ornithine lipids are known to induce potent host immune responses, including B-lymphocyte mitogenicity, adjuvanticity and macrophage activation. Yet, despite their widespread occurrence in Eubacteria, and the diverse biological effects they elicit in mammals, their physiological role in bacterial cells remained hitherto poorly defined. Our findings now indicate that under certain bacterial growth conditions ornithine lipids are crucial for optimal steady-state amounts of some extracytoplasmic proteins, including several c-type cytochromes, and attribute them a novel and important biological function.
Aygun-Sunar
Semra
S
Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia, PA 19104, USA.
Mandaci
Sevnur
S
Koch
Hans-George
HG
Murray
Ian V J
IV
Goldfine
Howard
H
Daldal
Fevzi
F
D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000235:genetics / Q000378:metabolism; D018628:Gene Dosage; D005816:Genetic Complementation Test; D008055:Lipids / Q000737:chemistry / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009952:Ornithine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000235:genetics / Q000378:metabolism*
D003574:Cytochrome c Group; D008055:Lipids; D008565:Membrane Proteins; C080693:cytochrome Cy; C051524:ornithine containing aminolipid; D009952:Ornithine; C414443:cbb3 oxidase; D003576:Electron Transport Complex IV