Ectoine can stabilize biological molecules using preferential exclusion. According to theoretical assumptions, osmolytes (e.g. ectoine) have the ability to bind water, which leads to the separation of their molecules from the protein surface and the associated preferential hydration of the protein, while increasing its stability. The properties of ectoine affect the stabilization of protein-lipid cell membranes, increase their fluidity and mobility of lipids (fats). What does this mean in practice?
The mechanism of stabilization of biological molecules by ectoine explains the theory of preferential exclusion. According to its assumptions, extremolites are distant from the surface of cellular proteins, but they affect the increase in the number of water molecules in the immediate vicinity of the protein. It's so-called preferential hydration (hydration), which positively affects the stability of the protein (increases it).
Ectoine exhibits cosmotropic properties: the ability to bind water molecules and embed them into complexes.
The high salt concentration in the aqueous solution disturbs the structure of liquid water and causes its molecules to become immobilized, which become inaccessible to hydrophobic macromolecules (e.g. proteins). However, thanks to the presence of ectoine (compensating substance), a protective effect is possible, consisting in the expansion of the hydrogen bond network and re-ordering of water molecules.
Ectoine strengthens the structure of water molecules and slows down the diffusion of water molecules accumulated around the protein. Ectoine and water complexes surround protein, lipid and nucleic acid molecules, forming a protective water jacket around them. The protective coating (formed by the binding of water by ectoine) lasts for a long time and protects cells from dehydration (dehydration).
In addition to forming the hydration shell of proteins, ectoine has a beneficial effect on the stability of the DNA helix. It protects nucleic acids from damage, inhibiting the harmful effects of reactive oxygen species and preventing damage that causes ultraviolet radiation.
As we mentioned, ectoine, due to its properties, causes the stabilization of protein-lipid cell membranes and increases their fluidity, which can induce the expression of many genes, e.g. genes regulating the response to thermal stress. Understanding this osmoprotective mechanism requires a brief repeat of microbiology.
The cell membrane is a lipid bilayer (proteins also belong to the main components of biological membranes), which separates the interior of the cell from the external environment, regulates transport between the cell and the external environment, and surrounds internal organelles.
The cell membrane is described as a liquid mosaic because the lipid molecules in the bilayer move within it (virtually all membrane components are moving). Environmental conditions are factors that determine the more or less dynamic nature of a membrane, which (in effect) may resemble a gel or a solid. The cell regulates the fluidity of membranes (as needed), synthesizing the appropriate types of molecules.
The lipid bilayer consists primarily of phospholipids - fats with a phosphorus group attached. In their structure, there is a phosphor end with hydrophilic properties (the so-called head that tends to combine with water) and hydrophobic ends (hydrophobic part - tail) with an affinity for fats.
The lipid layers in the bilayer structure are arranged in a characteristic way: their hydrophobic, hydrocarbon chains are directed inside the bilayer, and the hydrophilic parts (polar heads) are directed outside - they are on the surface of the bilayer and have contact with water. Therefore, the lipid bilayer is a barrier that is difficult to overcome by polar (water-soluble) molecules.
The stabilization of the lipid bilayer structure depends, among others from forming hydrogen bonds between polar heads and water molecules. Here, the ectoine molecule enters the arena, which (through hydrogen bonds) binds hydrophilic molecules on one side, and hydrophobic lipid chains of cell membranes on the other. Thus, ectoine enables the introduction of water molecules between hydrophilic phospholipid heads. As a consequence, cell membranes widen and hydrate, their tension and elasticity improve.
Thanks to ectoine, a protective coating forms on the surface of cell membranes, which prevents the harmful effects of exogenous (external) factors.