The Keith Peters Building
Paracoccus denitrificans oxidative phosphorylation, retentions, gains, losses, and lessons en route to mitochondria
There are many similarities between the oxidative phosphorylation apparatus of mitochondria and those found in the cytoplasmic membranes of alpha-proteobacteria, exemplified by Paracoccus denitrificans, the choice of which will be explained. These similarities will be reviewed alongside consideration of the differences between mitochondrial and bacterial counterparts, as well as the loss from the modern mitochondria of many of the bacterial respiratory proteins. The assembly of c-type cytochromes is of particular evolutionary interest as the post-translational apparatus used in the alpha-proteobacteria is found in plants, and for example in other eukyarotic species, including algae of various kinds and jakobids, but has been superseded by different systems in mitochondria of metazoans and trypanosomatids. All mitochondrial cytochromes c have the N-terminal sequence feature that is recognised by the metazoan apparatue whereas the bacterial counterparts do not, suggesting that the loss of the bacterial system from eukaryotes occurred in the context of an already present recognition sequence in the eukaryotic cytochromes. Interestingly, in the case of cytochromes c1 the putative recognition features for the metazoans appear to be substantially already present in the bacterial proteins. The ability to prepare from P. denitrificans inverted membrane vesicles with classic respiratory control presents a valuable system from which to draw lessons concerning the long debated topic of what controls the rates of respiration and ATP synthesis in mitochondria. If time allows, the recent discovery in two other labs of bacterial extracellular wires composed solely of mutimers of a hexheme c-type cytochrome will be illustrated.