Thread by @connor_rosen

The story about mitochondria being ~10° hotter than the rest of the cell, published @PLOSBiology a couple years ago (journals.plos.org/plosbiology/ar…) got some cool, albeit indirect, support recently @naturemethods… #Biophysics #CellBiology

The original paper, which was mainly based on the temperature-dependent fluorescence of a mitochondria-targeting probe, was accompanied by a “Primer” (journals.plos.org/plosbiology/ar…) highlighting potential flaws and implications, a special sort-of-peer-review step by PLOS Biology.

This new awesome resource @naturemethods - nature.com/articles/s4159… - offers some intriguing orthogonal validation. This is a proteome-wide study of protein thermal stability across 13 organisms, conducted using a mass-spec-based approach.

By measuring soluble protein left after heating at various temperatures, the thermal stability (really, a combination of stability + solubility, as the authors are careful to point out) of every protein in a sample can be measured in parallel.

On top of lots of cool stuff (Role of disorder in stability! Bacterial proteomes evolving closer to the edge of stability!), they find that mitochondrial respiratory chain enzymes, but not all mitochondrial proteins in general, have very high melting temperatures.

Additionally, they measure respiration rates in permeabilized cells (to bypass requirement for heat-sensitive glucose transporters), and match the finding about enzyme activities measured in the original paper - mitochondrial enzymes are perfectly happy running at 45°+!

The new study concludes that this “support[s] the hypothesis that proteins of the respiratory chain may have evolutionarily adapted to higher local temperatures by increasing their thermal stability”

Which is the exact question raised by the Primer accompanying the original paper - “Whether the mitochondrial enzymes are genuinely optimised for close to 50°C or just operate faster at that temperature before they fall to pieces is not clear.”

So, in exploring the evolution of proteome stability in a super cool resource, we have some orthogonal evidence that mitochondrial respiratory chain proteins really are evolved for higher temperatures. Of course, that doesn’t mean they’re actually running at 50°C.

But it’s an intriguing bit of evidence, and increases the probability that the original “50° mitochondria” report was on to something. It’s still unproven, and worth thinking about other ways to approach further proving (or disproving) it, but a cool spin on the problem!

That’s just one cool conclusion from this study on the “meltome”. It’s an amazing paper and dataset to examine for anyone interested in evolution of proteomes, sequence determinants of biophysical properties, and life at varying temperatures. Give it a read!