Protein subunits

Protein Subunits

A 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. Proteins that consist of more than one subunit are termed multimeric. Very large aggregates can be formed from protein subunits. For example, many thousands of actin molecules assemble into a microfilament.

Structure and Function

A protein subunit is not to be confused with domains. A domain is a part of the protein sequence and structure that can evolve, function, and exist independently of the rest of the protein chain. Subunits are a part of the quaternary structure of a protein, and whether a protein is monomeric (has one subunit) or multimeric (has more than one subunit) is a part of its quaternary structure.

Each protein subunit has a unique tertiary structure. A protein subunit is often composed of several secondary structure elements (such as alpha helices and beta sheets) that are connected by loop regions. They may also sometimes contain structural motifs like beta turns or omega loops. Protein subunits in a complex are also referred to as 'protomers' as they are associated with the protomer phenomenon in biochemistry.

Types of Protein Subunits

There are three types of protein subunits: alpha (α) subunit, beta (β) subunit, and gamma (γ) subunit. The alpha and beta subunits are identical and interact with one another, whereas the gamma subunit is distinct and interacts with the alpha subunit.

Role in Diseases

Protein subunits play a crucial role in the functioning of the body's cells. Any malfunction or abnormality in protein subunits can lead to various diseases. For example, mutations in the genes encoding the protein subunits of hemoglobin can cause sickle cell disease and thalassemia.

See Also

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