Protein quaternary structure
![Structure of the protein 1EFN, with focus on the quaternary structure.](/Images/godic/202502/05/Quaternary_structure4406.png")
In biochemistry, quaternary structure is the number and arrangement of multiple folded protein subunits in a multi-subunit complex. It includes organisations from simple dimers to large homooligomers and complexes with defined or variable numbers of subunits.