On a structural level, the constructive evolution of mitochondrial OXPHOS complexes can be visualized by highlighting MS-OPs in available crystal structures.
In summary, on a structural level the constructive evolution of mitochondrial ribosomes resembles that of OXPHOS complexes (I, III, IV, and V) in the following three aspects: 1) structural conservation of the core region; 2) peripheral distribution of mitochondrion-specific proteins; and 3) exclusion of mitochondrion-specific proteins from catalytically important surfaces.
No plan, no constructive evolution; just a rotting spot along Long Island Sound.
OXPHOS complex II is an even more striking example of a strict relationship between mitochondrial gene products and constructive evolution: It lacks MS-OPs in fungi and metazoa where complex II is exclusively nuclear encoded, but it does contain (lineage-specific) MS-OPs in plants (Millar et al. 2004), where mitochondrial complex II genes are also common (Adams et al. 2001).
In order to obtain structural insights into the constructive evolution of mitoribosomes, we determined the cryo-EM structure of a mitoribosome with a nonreduced amount of rRNA: The 73S mitoribosome from the filamentous fungus N. crassa (Michel et al. 1977; Neupert et al. 1979).
When we teach evolution to our students, we tend to focus on "constructive" evolution, the processes which lead to the development of novel or modified structures.
Hence, the constructive evolution of mitochondrial ribosomes and OXPHOS complexes may have opened up previously inaccessible but crucial evolutionary paths throughout mitochondrial and thus eukaryotic evolution.
Crucially, such effects are expected to be absent from analogous complexes that did not undergo constructive evolution, such as the ribosome and the cytochrome b 6f complex of chloroplasts.
In chloroplast genomes on the other hand, deleterious mutations accumulate much slower than in mitochondria (Lynch 1997), explaining why virtually no constructive evolution can be discerned in the photosynthetic apparatus and ribosomes of chloroplasts.
