Protein subunit

Protein subunit is a single protein molecule that assembles (or "coassembles") with other protein molecules to form a protein complex. Some naturally occurring proteins have a relatively small number of subunits and therefore described as oligomeric, for example hemoglobin. Others may consist of a very large number of subunits and therefore described as multimeric, for example microtubules. Indeed, many proteins are actually assemblies of multiple protein subunits.

Structure

The subunits of a protein may be identical, as in a homodimer, or different, as in a heterodimer. The quaternary structure of a protein is the spatial arrangement of its subunits and includes both their topology and their detailed atomic interactions. The topology of a protein's quaternary structure can be considered as a graph where nodes correspond to subunits and edges to connections.

Function

The function of a protein, especially those that are enzymes, often involves the close approach of several subunits. This allows the protein to coordinate its activity in a way that would be impossible with a single subunit. A good example of this is the ribosome, which is a large assembly of over 50 proteins.

See also

• Protein quaternary structure
• Protein tertiary structure
• Protein secondary structure
• Protein primary structure

References

Protein subunit Resources
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