Why Do Eukaryotes Have Bacterial Membranes?
There are three types of organisms on Earth today: Archaea, Bacteria and Eukaryotes. Essentially all those we can see (plants, mushrooms, animals) are Eukaryotes.
Phylogenetic evidence shows that Eukaryotes arose much later than the other two, from a merger of bacterial cells into an archaeal host. The internal bacteria would go on to become mitochondria, providing power for the whole cell, while the archaeal genome became the basis of what now is the nucleus.
Interestingly, the membranes of archaea and bacteria are drastically different. No archaea has ever been found with a bacterial membrane, or vice versa. The ancestral eukaryotic cell thus likely had an archaeal outer membrane but bacterial inner membranes. Yet all modern eukaryotes have only bacterial membranes, both internally and peripherally. At some point eukaryotes swapped their outer membranes from archaeal to bacterial.
Perhaps one set of phospholipids disrupted the membranes built with the other, creating pressure to be rid of one. But why did eukaryotes choose bacterial?
Genes for making archaeal phospholipids were already in the (proto)nucleus, while in modern eukaryotes, bacterial phospholipids have taken their place, transferred from the mitochondrial genome. Both the archaeal counterparts and the bacterial originals inside mitochondria were lost or repurposed. Eukaryotes went through the evolutionary trouble of replacing the perfectly functional archaeal originals with bacterial analogues. Why?
Mitochondria produce most of the power of the eukaryotic cell (as ATP), and they do so with ancestrally bacterial membrane proteins that sit on ancestrally bacterial membranes. Mismatches are lethal, as gravely demonstrated by mitochondrial diseases in humans. I suggest that this means bacterial lipids had to be kept, and I will use a combination of computational methods to test it.
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Sojo, V., C. Dessimoz, A. Pomiankowski, and N. Lane (2016). "Membrane proteins are dramatically less conserved than water-soluble proteins across the tree of life." Molecular Biology and Evolution 33, 11: 2874-2884.
Sojo, V. (2015). "On the biogenic origins of homochirality." Origins of Life and Evolution of Biospheres 45, 1-2: 219-224.
Sojo, V., A. Pomiankowski, and N. Lane (2014). "A bioenergetic basis for membrane divergence in archaea and bacteria." PLOS Biology 12, 8: e1001926.