- Protein subunit
structural biology, a protein subunit or subunit protein is a single protein moleculethat assembles (or "coassembles") with other protein molecules to form a "multimeric" or "oligomeric" protein. Many naturally-occurring proteins and enzymes are multimeric. Examples include: "oligomeric": hemoglobin, DNA polymerase, nucleosomes and "multimeric": ion channels, microtubules and other cytoskelotonproteins. The subunits of a multimeric proteinmay be identical, homologous or totally dissimilar and dedicated to disparate tasks. In some protein assemblies, one subunit may be referred to as a " regulatory subunit" and another as a " catalytic subunit." An enzyme composed of both regulatory and catalytic subunits when assembled is often referred to as a holoenzyme. One subunit is made of one polypeptidechain. A polypeptide chain has one genecoding for it - meaning that a protein must have one gene for each subunit.
A subunit is often named with a Greek or Roman letter, and the numbers of this type of subunit in a protein is indicated by a subscript. For example,
ATP synthasehas a type of subunit called α. Three of these are present in the ATP synthase molecule, and is therefore designated α3. Larger groups of subunits can also the specified, like α3β3-hexamer and c-ring.
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