Coupling efficiency in mitochondrial haplogroups

Testing the adaptive selection of human mtDNA haplogroups: an experimental bioenergetics approach
April 19, 2007.
 
The evolution of human mtDNA (mitochondrial DNA) has been characterized by the emergence of distinct haplogroups, which are associated with the major global ethnic groups and defined by the presence of specific mtDNA polymorphic variants. A recent analysis of complete mtDNA genome sequences has suggested that certain mtDNA haplogroups may have been positively selected as humans populated colder climates due to a decreased mitochondrial coupling efficiency, in turn leading to increased generation of heat instead of ATP synthesis by oxidative phosphorylation. If this is true, implying different evolutionary processes in different haplogroups, this could potentially void the usefulness of mtDNA as a genetic tool to study the timing of major events in evolutionary history. In this issue of the Biochemical Journal, Taku Amo and Martin Brand present experimental biochemical data to test this hypothesis. Measurements of the bioenergetic capacity of cybrid cells harbouring specific Arctic or tropical climate mtDNA haplogroups on a control nuclear background reveal no significant changes in coupling efficiency between the two groups, indicating that mtDNA remains a viable evolutionary tool to assess the timing of major events in the history of humans and other species.

Hmm, the other studies I’ve posted in the last few days cast a big shadow over the ‘neutral marker’ paradigm for mt DNA. I’m sure I’ve posted one that shows selection against L haplotypes in cold climates.

Were inefficient mitochondrial haplogroups selected during migrations of modern humans? A test using modular kinetic analysis of coupling in mitochondria from cybrid cell lines

We introduce a general test of the bioenergetic importance of mtDNA (mitochondrial DNA) variants: modular kinetic analysis of oxidative phosphorylation in mitochondria from cybrid cells with constant nuclear DNA but different mtDNA. We have applied this test to the hypothesis [Ruiz-Pesini, Mishmar, Brandon, Procaccio and Wallace (2004) Science 303, 223-226] that particular mtDNA haplogroups (specific combinations of polymorphisms) that cause lowered coupling efficiency, leading to generation of less ATP and more heat, were positively selected during radiations of modem humans into colder climates. Contrary to the predictions of this hypothesis, mitochondria from Arctic haplogroups had similar or even greater coupling efficiency than mitochondria from tropical haplogroups.

This one suggests that the haplotypes function differently in terms of efficiency. So does the next one.

Effects of Purifying and Adaptive Selection on Regional Variation in Human mtDNA

A phylogenetic analysis of 1125 global human mitochondrial DNA (mtDNA) sequences permitted positioning of all nucleotide substitutions according to their order of occurrence. The relative frequency and amino acid conservation of internal branch replacement mutations was found to increase from tropical Africa to temperate Europe and arctic northeastern Siberia. Particularly highly conserved amino acid substitutions were found at the roots of multiple mtDNA lineages from higher latitudes. These same lineages correlate with increased propensity for energy deficiency diseases as well as longevity. Thus, specific mtDNA replacement mutations permitted our ancestors to adapt to more northern climates, and these same variants are influencing our health today.

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