Some superheroes wear flashy costumes and capes that you can’t help but notice, but then there’s the unassuming tardigrade; the microscopic wonder beast with the astounding ability to survive extreme temperatures, radiation, and the vacuum of space! With multiple secret identities, including “water bear” and “moss piglet”, the discrete invertebrate has kept the key to its super survival skills under wraps until recently.
The damage suppressor protein (Dsup) from one species of tardigrade can protect human cells from damaging X-rays, and the lab of James Kadonaga (University of California, San Diego) has been exploring how it works. The talented team generated FLAG- and His6-tagged versions of Dsup and explored how it protects innocent chromatin from free radical villains.
They found that Dsup:
- Preferentially binds to individual nucleosomes
over isolated DNA, regardless of the sequence, in gel mobility shift assays
- Two Dsup molecules likely bind to each nucleosome because two distinct bands appear on the gel
- Does not interfere with the ability of plasmid
DNA to form supercoiled structures when nucleosome assembly is induced
- When the newly formed nucleosomes were separated with MNase digestion and run on a gel, Dsup was found primarily at mono- and dinucleosomes
- Doesn’t interfere with the natural nucleosome binding protein, histone H1 in the formation of nucleosomes
- Is very similar to a protein in another tardigrade species, and that both proteins bind to mononucleosomes and protect chromatin from degradation by hydroxyl radicals
They also found that Dsup contains a DNA-binding sequence that’s remarkably similar to a nucleosome binding protein found in humans (HMGN), and it’s necessary for chromatin binding.
It might seem that we’ve unmasked all the mysteries of Dsup, but tardigrades are keeping at least one more secret about their superpower: HMGN is only found in vertebrates, so how did its homolog end up in the water bear genome? While we wait for the sequel, bioengineers can start using Dsup to protect valuable human cell lines, and you can dig up the details of this saga in eLife, October 2019.