Function
Tardigrades (Ramazzottius varieornatus), informally known as water bears, are viewed as the most resilient organisms on the planet. They have the capability to shut down metabolic processes and undergo anydrobiosis, a dehydrated state in which they can exist even in the vacuum of space. One of the secrets to their success may be 5xn9, a secreted heat soluble protein. The protein shields organelles and extracellular components during dehydration to improve desiccation tolerance and prevent crystallization.
Structural highlights
The 5xn9 protein derives its function primarily from several key sites. The first are the , two large beta-sheets that coil to form a barrel-like structure that allows hydrophobic residues to form unusual networks of hydrogen bonds.
Beta barrels are commonly seen in membrane proteins and often contain alternating residues of hydrophobic and hydrophilic amino acids, as can be seen with hydrophobic regions in red and hydrophilic regions in turquoise. The particular beta barrel on 5xn9 is very similar to that of fatty acid binding proteins (FABPs).
Other components of interests on 5xn9 include protein modification binding sites. Zinc is shown in blue and magnesium in magenta. These and other post-translational modifications play an important role in determining the structure of 5xn9 and improving its tolerance to dehydration.
