EPR approaches to disorder in proteins

Nature can be messy. Disorder often accompanies natural processes and in some cases may even be required for function. For biochemical and biophysical techniques, disordered systems are challenging, to the degree that traditional methods of structure determination either cannot be applied at all, or are severely limited. The methods suffer from broadening effects due to heterogeneity and multi-component spectra are often impossible to interpret.

The growing understanding that disorder and heterogeneity are important in biological processes and the increasing evidence that disordered regions in proteins may be functional,¹  make it timely to take a current-day look at these subjects. The discovery in 1998²  of intrinsically disordered proteins, or of proteins that function on account of disordered regions,³  is reflected in a textbook.⁴  Fig. 1 shows in a cartoon-fashion the interactions and different conformations that flexible proteins can adopt.