Quaternary structure of proteins
The quaternary structure of proteins is formed by the union of weak bonds of several polypeptide chains with tertiary structure to form a protein complex. Each of these polypeptide chains is called a protomer.
In terms of protein structure levels, it can be more broadly shaped than normal. It includes the range of oligomeric proteins, that is, those proteins that consist of more than one polypeptide chain, in which there may also be an allosteric behavior according to the concerted method of Jacques Monod.
The quaternary structure derives from the conjunction of several amino acid chains that, thanks to their union, carry out the process of disjunction, thus giving a favorable result to already increased proteins. It presents several different polypeptides and its functional structure requires the interaction between two or more similar or different amino acid chains.
Through the quaternary protein organization, structures of great biological importance such as microtubules, microfilaments, virus capsomeres and enzyme complexes are formed. Collagen fibrils found in the extracellular space of connective tissue are also constituted by the aggregation of tropocollagen polypeptide chains.
In general, the quaternary structure gives the function of the protein, but there are examples of proteins active outside their quaternary complex. Subunit arrangements may confer on the quaternary complex or point of symmetry axis, but this is not required. Proteins that are made in this way generally have a molecular weight greater than 50,000, an example of this is hemoglobin.
Allostery deals with enzymatic regulation of the properties of a multimeric protein. Regarding the quaternary structure, allosterism can be captured as a consequence of the relative movement of a monomer in the multimeric properties. Hemoglobin provides a well-studied example, but it is not the only one.