Complexed proteins are linked by non-covalent protein–protein interactions. These complexes function to perform many biological processes inside the cell.
A multiprotein complex (or protein complex) is a group of two or more associated
chains. The different chains may have different functions. Multiprotein complexes are examples of the
level of protein organization. An example of a protein complex is the Bacillus amyloliquefaciens ribonuclease barnase and its inhibitor barstar, shown below.