Intrinsically disordered proteins (IDPs) have very limited innate structure in solution but gain shape specifically when interacting with partner molecules such as proteins or RNA; however, their resultant structure is often dictated by this interaction.  In addition, some proteins have sections of sequence without structure, termed intrinsically disordered regions (IDRs), that also gain structure on interaction.  Having different shapes with different partners means they are functionally, as well as structurally flexible, making them centrally important to signalling pathways and as regulation/control factors for example.  IDPs (and IDRs if capable of being isolated from the rest of the protein) have a distinct SRCD spectral appearance in solution which means that changes in their spectra that arise through interactions offer an ideal opportunity to gain insight into what is happening both structurally and functionally. In addition, SRCD studies have demonstrated that when the solvating water is removed from these proteins, generating a film, there is a gain in structure and more CD transition bands can be measured into the lower VUV wavelength region because the water absorption band is not present
Myelin is the insulating sheath that is formed in the central (CNS) and peripheral nervous systems (PNS) to surround nerve cell axons thereby increasing and maintaining the electrical impulse, the action potential, sent along them. Formed mostly of lipids, there are specific proteins within the myelin components whose roles are to structure the myelin into linked layers.  Two of these proteins are myelin basic protein (MBP), an IDP primarily in the CNS, and myelin protein zero (P0) which contains an IDR section (P0ct) and is key within the PNS. MBP and P0ct were employed in a study which used SRCD data as a key factor to establish if there was any significance to the predictions of their IDP and IDR protein structures generated by Alphafold2, an artificial intelligence program developed by DeepMind.  PDB2CD, a package that generates SRCD spectra from protein atomic coordinates, was used to calculate spectra from the Alphafold2 structures, and these spectra were then compared against SRCD experimental spectra collected from the MBP and P0ct proteins in various ambient conditions; solution, detergent and lipid-bound states.  The study reported that from the SRCD comparisons, the structures predicted by Alphafold2 for MBP and P0ct bore a strong resemblance to those when they were bound to the lipid membrane.