A ‘fluffy
cloud’ of protein shields water bears’ DNA from radiation, drying and other damage
Tardigrades
may partly owe their ability to survive outer space to having the molecular
equivalent of cotton candy.
Water bears,
as the creatures are also known, can famously survive just about anything (SN:
7/14/17), including being bombarded with X-rays or cosmic rays, or being doused
in hydrogen peroxide. Such radiation and chemical exposure result in production
of DNA-damaging hydroxyl radicals, molecules composed of oxygen and hydrogen.
Previous
research indicated that a protein called Dsup, for damage suppressor, shields
the tardigrade species Ramazzottius varieornatus from radiation. When added to
human cells, the protein also protects against radiation. Now researchers have
found out how.
Dsup
surrounds nucleosomes — DNA wound around proteins called histones — “like a fluffy cloud of cotton candy,â€
molecular biologist James Kadonaga of the University of California, San Diego
in La Jolla and colleagues report October 1 in eLife. That cloud keeps hydroxyl
radicals away from DNA.
Another
tardigrade species Hypsibius exemplaris, previously thought to lack Dsup, has
its own version of the protective protein, the researchers discovered. Only
about 26 percent of the amino acids in the two species’ Dsup proteins are
alike, but both shroud DNA against damage.
Kadonaga
says the proteins probably evolved to protect tardigrades from hydroxy radicals
when the moss-dwellers are dried out, a frequent occurrence (SN: 12/16/15).
Drying increases the concentration of DNA-dinging radicals in cells. And damage
can’t be repaired while the animals are dormant in their desiccated state.
Since X-rays also form hydroxy radicals, tardigrades “just happen to be X-ray
resistant,†too, he says.
Humans have
similar proteins called high mobility group nucleosome-binding proteins or
HMGNs. But the researchers don’t yet know whether the human proteins also form
a similar shield against DNA-damaging chemicals.
From source: https://www.sciencenews.org/article/tardigrades-dna-damage-radiation-death
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