Folding of protein chain is due to:
Hydrophobic residues are largely buried in the protein interior, away from water and the number of hydrogen bonds and ionic interactions within protein is maximized, thus reducing the number of hydrogen bonding & ionic group that are not paired with suitable partner.
Because of favourable free energy change and cooperative bonding (i.e. one bond favours the formation of next bond), the hydrogen bonds often have an important role in the protein folding process.
Amide bond
Hydrogen bond
Phosphodiesterase bond
Disulphide bond