Protein Quaternary Structure: Subunit–Subunit Interactions

Abstract

The quaternary structure of proteins is the highest level of structural organization observed in these macromolecules. The multimeric proteins that result from quaternary structure formation involve the association of protein subunits through hydrophobic and electrostatic interactions. Protein quaternary structure has important implications for protein folding and function.

Keywords: protein–protein interaction; subunit; oligomer; molecular recognition; multimer

Figure 1.

Molscript diagrams depicting the secondary structure elements and the quaternary structure of (a) homodimeric interleukin 8; (b) heterodimeric human chorionic gonadotrophin; (c) homodimeric HIV‐1 protease; (d) heterotetrameric human haemoglobin. In each diagram the protein subunits are differentiated by colour, and in (d) one αβ‐protomer of haemoglobin is coloured red and one green. The haem groups in each subunit shown in (d) are depicted by ball‐and‐stick representations.

Figure 2.

Modes of association in multimeric proteins: (a) isologous, in which the binding sets (indicated by the letters ‘a’ and ‘b’) are identical; (b) heterologous, in which the binding sets (indicated by the letters ‘a’, ‘b’, ‘c’ and ‘d’) are not identical. Adapted from Monod et al., .

Figure 3.

The accessible surface area of a protein. The diagram shows just two atoms, with a probe sphere (with a radius of R) defining the accessible surface.

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Further Reading

Banaszak LJ, Birktoft JJ and Barry CD (1981) Protein–protein interactions and protein structures. In: Protein–Protein Interactions, pp. 31–128. New York: Wiley.

Chan WW (1976) The relationship between quaternary structure and enzyme activity. Trends in Biological Sciences 11: 258–260.

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Jones, Susan, and Thornton, Janet M(Apr 2001) Protein Quaternary Structure: Subunit–Subunit Interactions. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003120]