Interactions that contribute to protein folding

Protein structure is stabilized by following interactions:

Covalent bond: Covalent bonds are formed when two atoms share equal electrons. Amino acids linked with each other through covalent peptide bonds and from dipeptide, tripeptide, oligopeptide and polypeptide. Covalent bonds are important to maintain the primary structure of protein. 

 Covalent disulphide bridges (-S-S-): Sulphur containing amino acid (cysteines) are involved in forming covalent disulphide bonds and play a pivotal role to maintain the tertiary structure of proteins.

Electrostatic interaction: This type of interactions is occur between oppositely charged molecules. in protein electrostatic interaction occur due to side chains of amino acids. Generally electrostatic interactions are found in tertiary and quaternary structure of proteins, and these interactions occur through their oppositely charged side chains (e.g., lysine and aspartic acid).

Hydrogen bond: Hydrogen bonds formed between hydrogen and electronegative atoms e.g., oxygen and nitrogen. Hydrogen bonds are the main reason behind the great stability of secondary, tertiary and quaternary structure of proteins.

van der Waals bonds: When the force of attraction and repulsion are equal it is known as London dispersion forces; and weak interactions resulting from this dispersive force are known as van der Waals bonds. These bonds are important in maintaining the three-dimensional structure of protein.

Hydrophobic bonds: Side chains of non-polar amino acids like valine etc. are involved in hydrophobic interactions. This interaction helps to minimize the contact between water molecule and side chains of non-polar amino acids. This provide stability to protein structure and important in folding.

Co-ordinate bond: Such type of interaction occur because in only one atom share the pair of electrons which are involve in bonding. Coordinate bond is found in metalloprotein.