Osmoprotectant
Encyclopedia
Osmoprotectants or compatible solutes are small molecules that act as osmolyte
s and help organisms survive extreme osmotic stress. Examples include betaines, amino acid
s, and the sugar trehalose
. These molecules accumulate in cells and balance the osmotic difference between the cell's surroundings and the cytosol
. In extreme cases, such as in bdelloid rotifers, tardigrades, brine shrimp
and nematodes, these molecules can allow cells to survive being completely dried out and let them enter a state of suspended animation called cryptobiosis
. In this state the cytosol and osmoprotectants become a glass-like solid that helps stabilize protein
s and cell membrane
s from the damaging effects of desiccation.
Compatible solutes have also been shown to play a protective role by maintaining enzyme activity through freeze-thaw cycles and at higher temperatures. Their specific action is unknown but is thought that they are preferentially excluded from the proteins interface due to their propensity to form water structures.
Osmolyte
Osmolytes are compounds affecting osmosis. They are soluble in the solution within a cell, or in the surrounding fluid, e.g. as plasma osmolytes. They play a role in maintaining cell volume and fluid balance. For example, when a cell swells due to external osmotic pressure, membrane channels open...
s and help organisms survive extreme osmotic stress. Examples include betaines, amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
s, and the sugar trehalose
Trehalose
Trehalose, also known as mycose or tremalose, is a natural alpha-linked disaccharide formed by an α,α-1,1-glucoside bond between two α-glucose units. In 1832, H.A.L. Wiggers discovered trehalose in an ergot of rye, and in 1859 Marcellin Berthelot isolated it from trehala manna, a substance made...
. These molecules accumulate in cells and balance the osmotic difference between the cell's surroundings and the cytosol
Cytosol
The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....
. In extreme cases, such as in bdelloid rotifers, tardigrades, brine shrimp
Brine shrimp
Artemia is a genus of aquatic crustaceans known as brine shrimp. Artemia, the only genus in the family Artemiidae, has changed little externally since the Triassic period...
and nematodes, these molecules can allow cells to survive being completely dried out and let them enter a state of suspended animation called cryptobiosis
Cryptobiosis
Cryptobiosis is an ametabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all metabolic procedures stop, preventing reproduction, development, and repair...
. In this state the cytosol and osmoprotectants become a glass-like solid that helps stabilize protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
s and cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
s from the damaging effects of desiccation.
See also
- OsmoregulationOsmoregulationOsmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
- ProlineProlineProline is an α-amino acid, one of the twenty DNA-encoded amino acids. Its codons are CCU, CCC, CCA, and CCG. It is not an essential amino acid, which means that the human body can synthesize it. It is unique among the 20 protein-forming amino acids in that the α-amino group is secondary...
- EctoineEctoineEctoine is a natural compound found in several species of bacteria. It is a compatible solute which serves as a protective substance by acting as an osmolyte and thus helps organisms survive extreme osmotic stress...
Compatible solutes have also been shown to play a protective role by maintaining enzyme activity through freeze-thaw cycles and at higher temperatures. Their specific action is unknown but is thought that they are preferentially excluded from the proteins interface due to their propensity to form water structures.