Quaternary structure involves severalpolypeptides:
Oligomers
Heteromers
These subunits interact with eachother through the usual weakinteraction forces (H bonds, Van derWaals, ionic interactions, hydrophobicinteractions) and/or though disulfidebonds;
For aquous proteins, frequently, butnot always, the interface between twosubunits is made of hydrophobicamino acids.
For membrane-bound proteins, theamino acids at the interface betweenthe subunits are usually hydrophilic;