proteins are vital macromolecules, at both cellular and systemic levels, but they rarely act alone. Diverse essential molecular processes within a cell are carried out by molecular machines that are built from a large number of protein components organized by their Protein-Proteins interaction (PPI). Indeed, these interactions are at the core of the entire interactomics system of any living cell and so, unsurprisingly, aberrant PPIs are on the basis of multiple diseases, such as Creutzfeld-Jacob, Alzheimer’s disease, and cancer.
There are several different types of forces acting on/within a protein molecule. These include:
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Stabilizing bonds involved in Proteins:
1. The covalent bonds:
These strong bonds result from sharing of electrons between two atoms. There are four different types.
- The peptide bond -CO-NH-bond is responsible for the formation of the carbon skeleton, of the primary structure of proteins.An amide bond is formed between the α carboxylic function of an amino acid and the α amino function of another amino acid.
- The carbon-carbon bond -CO-CH is in fact in the amino acids making up the protein but plays a role in the formation of the skeleton.
- The disulfide bridges are found in abundance in proteins and are characteristic of the tertiary structure of globular proteins.They are commonly found in fibrous proteins. The bridge stands (optionally) between two cysteins and is broken by the action of mercaptoethanol.
- The desmosines bridges connect four molecules of lysine. Characteristics of elastin, they are formed by lysyl oxidase.
2. The Non-Covalent Bonds:
a. The ionic bonds:
The ionic bonds are weak bonds resulting from the attraction between two oppositely charged polar groups . Thus meet these bonds between the carboxyl group of an acidic amino acid (glutamate or aspartate) and the nitrogen-containing group of a basic amino acid (lysine, histidine, arginine). These connections can be made within a same chain, the polypeptide folding. These bonds are the strongest after the covalent bonds. They depend on the pH and salt concentrations. They have a certain importance in the relationship between the protein and other molecules.
Two electronegative atoms unevenly shared hydrogen. An atom is covalently bonded to H is the donor atom. The other atom is the acceptor atom. Generally we see this connection between the elements of two peptide bonds. They are also involving radicals polar amino acids. They are weak and unstable, but these defects are compensated by their large number that allows them to have an essential role in maintaining the secondary tertiary structure. Hydrogen bonds gain power when the three atoms are aligned on the same axis.
c.Van der Waals forces:
This connection is made to any atom but requires a distance between atoms low: less than 5 angstroms . Each atom has electronic temporary fluctuations making it a transition dipole. This explains why two atoms, even neutral, can develop a weak interaction, the force of attraction of Van der Waals . Their weakness is offset by their large number, especially when adjusting two macromolecular surfaces.
They are between two non-polar molecules. In the presence of water, they tend to come together to exclude water. For example in the soluble globular proteins, the hydrophobic region (the non-polar groups) is buried within the molecule, excluding water. This phenomenon stabilizes the tertiary structures.