Allostery and Quaternary Structure
Quaternary proteins are multisubunit proteins held in relation to each other through non-covalent forces. Allosteric proteins have another site which binds an effector molecule. The allosteric site ligand binding influences the binding of substrate in a positive or negative (inhibitory) manner. The presence of sigmoidal (as opposed to hyperbolic) kinetics is a valuable clue in the identification of an allosteric protein. Much of our understanding of cooperativity comes from the study of hemoglobin. Ligand binding induces conformational changes in a protein which historically have been investigated using X-ray crystallography. Two models (MWC and KNF) are used to relate conformational change and function. As additional allosteric proteins are studied and new techniques are applied, some long-standing assumptions are being challenged in the absolute, though the assumptions remain true in the general.
Quaternary proteins are proteins in which two or more polypeptides...