Unstructured Proteins Help Tardigrades Survive Desiccation

  • Hardy, microscopic animals called tardigrades, also known as water bears, can survive desiccation. Until now, it wasn’t clear exactly how.
  • The results of a study published in Molecular Cell  (March 16) suggest that proteins lacking stable 3-D structures, called tardigrade-specific intrinsically disordered proteins (TDPs), form glass-like solids that protect the animals during drying.
  • Other organisms achieve desiccation tolerance with a sugar called trehalose, which forms glass-like solids upon drying. For years, researchers assumed that tardigrades used trehalose, too, but many species of water bears only express small amounts of the sugar—likely not enough to confer the substance’s preservative capabilities.
  • TDPs “seem to work by a mechanism which is similar to this sugar, trehalose.

More Details:

  • They are considered the world’s toughest animals, capable of living anywhere from the bottom of the ocean to 5,500 metres up a Himalayan mountain.
  • They can be boiled at temperatures of up to 150 degrees Celsius or frozen to near absolute zero, but still tardigrades, tiny, Muppet-like creatures also known as water bears or moss piglets, just will not die.
  • They have even been found on the outside of the International Space Station, where the lack of pressure would kill a human in minutes at most.
  • The big takeaway from the study is that tardigrades have evolved unique genes that allow them to survive drying out.
  • In addition, the proteins that these genes encode can be used to protect other biological material like bacteria, yeast, and certain enzymes – from desiccation.
  • These proteins have been named TDPs or ‘tardigrade-specific intrinsically disordered proteins’ in honour of the 1mm-long creatures who evolved to have them.
  • Previously it had been thought that a type of sugar called trehelose, which is found in other organisms including brine shrimp, was the secret behind the tardigrade’s ability to return from the dead after being dried out for up to 10 years.
  • Following the discovery, reported in the journal Molecular Cell, the scientist put the genes into yeast and bacteria, which then gained the same properties as the tardigrades.
  • TDPs could be used to protect crops from drought and to preserve medicines without using a refrigerator.

About Tardigrades:

  • Tardigrades are microscopic animals that survive a remarkable array of stresses, including desiccation. How tardigrades survive desiccation has remained a mystery for more than 250 years.
  • Trehalose, a disaccharide essential for several organisms to survive drying, is detected at low levels or not at all in some tardigrade species, indicating that tardigrades possess potentially novel mechanisms for surviving desiccation.
  • Here we show that tardigrade-specific intrinsically disordered proteins (TDPs) are essential for desiccation tolerance.
  • TDP genes are constitutively expressed at high levels or induced during desiccation in multiple tardigrade species.
  • TDPs are required for tardigrade desiccation tolerance, and these genes are sufficient to increase desiccation tolerance when expressed in heterologous systems.
  • TDPs form non-crystalline amorphous solids (vitrify) upon desiccation, and this vitrified state mirrors their protective capabilities.
  • Our study identifies TDPs as functional mediators of tardigrade desiccation tolerance, expanding our knowledge of the roles and diversity of disordered proteins involved in stress tolerance.

Source: The Scientist