Protein quaternary structure

It includes organizations from simple dimers to large homooligomers and complexes with defined or variable numbers of subunits.

[2] Examples of proteins with quaternary structure include hemoglobin, DNA polymerase, ribosomes, antibodies, and ion channels.

It is through such changes, which underlie cooperativity and allostery in "multimeric" enzymes, that many proteins undergo regulation and perform their physiological function.

The above definition follows a classical approach to biochemistry, established at times when the distinction between a protein and a functional, proteinaceous unit was difficult to elucidate.

Several molecular machines are also found in the cell, such as the proteasome (four heptameric rings = 28 subunits), the transcription complex and the spliceosome.

For example, a tetrameric protein may have one four-fold rotation axis, i.e. point group symmetry 4 or C4.

However, these may sometimes be applicable; for example, the experimenter may apply SDS-PAGE after first treating the intact complex with chemical cross-link reagents.

Some bioinformatics methods have been developed for predicting the quaternary structural attributes of proteins based on their sequence information by using various modes of pseudo amino acid composition.

One such development is AlphaFold-Multimer[10] built upon the AlphaFold model for predicting protein tertiary structure.

Protein quaternary structure also plays an important role in certain cell signaling pathways.

[12] When multiple copies of a polypeptide encoded by a gene form a quaternary complex, this protein structure is referred to as a multimer.

Intragenic complementation appears to be common and has been studied in many different genes in a variety of organisms including the fungi Neurospora crassa, Saccharomyces cerevisiae and Schizosaccharomyces pombe; the bacterium Salmonella typhimurium; the virus bacteriophage T4,[14] an RNA virus,[15] and humans.

[17] Direct interaction of two nascent proteins emerging from nearby ribosomes appears to be a general mechanism for oligomer formation.