3.7: Intrinsically Disordered Proteins
Intrinsically disordered proteins are a group of proteins that do not fold into specific three-dimensional structures. Their structural flexibility allows them to complement ordered proteins to perform functions that are inaccessible to rigid structures. They are more common in eukaryotes than prokaryotes and may either be exclusively intrinsically disordered or hybrid proteins, consisting of a mix of ordered and disordered regions. The absence of a rigid structure in these proteins can be attributed to an abundance of polar and charged amino acid residues and relatively fewer hydrophobic amino acids, promoting an ordered structure.
Several factors influence the shape and level of disorder in a protein, such as pH and temperature. Additionally, other proteins that they bind to or associate with can also influence their shape. This binding can occur through multiple binding sites and can result in the permanent or temporary folding of an intrinsically disordered protein or region. Structural changes are made due to molecular recognition features —short, interaction amenable fragments of disordered proteins that can readily undergo disorder-to-order transitions upon binding to other proteins with defined structures.
Post-translational modifications during or after protein synthesis also contribute to the structure of intrinsically disordered proteins. These could include enzymatic cleavage of a peptide bond in the precursor protein, the formation of disulfide bonds, and covalent modifications of proteins with other molecules or chemical groups.