Proteins estimating distances between parts

Estimates of distances between parts of proteins or assemblies of proteins with other species can be made by exploiting diffraction, energy transfer, and dipolar interactions. The most common of these methods have been X-ray diffraction, fluorescence energy transfer, NMR, and EPR. Each physical method provides a different perspective, and multiple methods are needed to achieve a full view (2). For each method, key questions include for what species is it appropriate, what range of distances can be measured, how sensitive is the method to distributions in distance or in orientation, and what is the accuracy and precision of the method. Furthermore, one wants to know whether a method is sensitive to dynamics, and whether this sensitivity blurs the distance measurement or is an opportunity to measure dynamics of distances. 

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