In structural biology, a protein subunit or subunit protein is a double proteinmolecule that assembles (or "coassembles") with other protein molecules to form a multimeric or oligomeric protein. Many naturally-occurring proteins and enzymes are multimeric. Examples include hemoglobin, ion channels, DNA polymerase, nucleosomes and microtubules. The subunits of a multimeric protein may 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 polypeptide chain. A polypeptide chain have one gene coding for it - meaning that a protein must have one gene for each subunit. Structural biology is a branch of molecular biology concerned with the study of the architecture and shape of biological macromolecules--proteins and nucleic acids in particular—and what causes them to have the structures they have. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... In science, a molecule is a group of atoms in a definite arrangement held together by chemical bonds. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... 3-dimensional structure of hemoglobin. ... Ion channels are pore-forming proteins that help to establish and control the small voltage gradient that exists across the plasma membrane of all living cells (see cell potential) by allowing the flow of ions down their electrochemical gradient. ... 3D structure of the DNA-binding helix-hairpin-helix motifs in human DNA polymerase beta A DNA polymerase is an enzyme that assists in DNA replication. ... A nucleosome is a unit made of DNA and histones. ... Microtubules are one of the components of the cytoskeleton. ... In biology, homology is any similarity between structures that is due to their shared ancestry. ... In biochemistry, holoenzyme may refer either to the complete and operative form of an enzyme with multiple protein subunits or to the combination of an apoenzyme with its cofactor. ... Peptides are the family of molecules formed from the linking, in a defined order, of various amino acids. ... For a non-technical introduction to the topic, see Introduction to Genetics. ...
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 synthase has 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. An ATP synthase (EC 3. ...
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