Proteins – Quaternary Structure & Overview

The quaternary structure of a protein involves the association of folded polypeptide chains into a mature, active protein.

  • This can be a single polypeptide chain (monomer), 2 chains (dimer), 3 chains (trimer), 4 chains (tetramer) and so on…
  • The associated chains can be identical or different.

Some quaternary structure require additional polypeptide chains (which were removed during production) in order to achieve a working protein state (eg. Mature insulin). There are also structures which will revert to their original shape once broken, as the order is set in the primary structure of Amino Acids.

With Insulin, a helper amino acid strand is used to ‘hold’ two sequences in place, allowing the formation of disulphide bridges. I’ve tried to illustrate before and after:

S is the signal chain, while B acts as a support structure during disulphide bridge formation between A and C.

– An Overview

  • Primary Structure – The sequence of Amino acids on a chain.
  • Secondary Structure – The 3D relationship between Amino Acids – leading to α helix, β pleated sheet etc.
  • Tertiary Structure – The 3D relationship between parts of the above structure.
  • Quaternary Structure – The number of and relationship between amino acid chains (seperate tertiary structures).