Despite the asymmetry of their building blocks, the 1-amino acids proteins display symmetry, quasissymmetry, and pseudosymmetry at all levels of 3-D structure:

formation of secondary structure by repetitive polypeptide main chain conformations; formation of super-secondary structure by repetitive arrangements of secondary structural elements along the polypeptide chain; formation of oligomers from protein subunits. Symmetrical oligomeric structures may specific morphological functions as containers or display regulatory and polyvalent binding properties.

Large proteins are constructed as oligomeres for reasons of error control in biosynthesis, control of assembly, gain of stability over monomeric species.

Examples of complexes displaying all crystallographic point groups have been found and many more exist using non-crystallographic rotational symmetries. Of the overwhelming wealth of documented symmetrical oligomers I will restrict discussion to examples that form closed containers for the purpose of protein degradation and protein folding.

These structures highlight aspects of
symmetry
pseudosymmetry
symmetry mismatch
multivalent binding
regulation of assembly and activity