Triple Isotopic Substitution Method in Small-Angle Neutron Scattering: Application to Some Problems of Structural Biology

Abstract

The triple isotopic substitution (TIS) method is based on the analysis of a scattering curve which is the difference between the scattering of two solutions containing appropriately deuterium-labelled particles. A necessary condition for the application of the method is that the two solutions are identical in all respects except for the extent of the deuterium label. Such an experimental scheme has allowed a number of unique physical experiments to be performed, the main ones being: (1) elimination of the contribution of the interparticle interference; (2) addition of both small- and large-sized foreign particles to those studied without distortions of the structural data; (3) highlighting of individual (quite small) regions in the molecules; (4) suppression of the dimerization contribution to the scattering curve. The application of this method is of special interest for studying the mutual three-dimensional disposition of individual small regions of molecules (3D mapping) and for investigating the geometrical properties of the surfaces of globular proteins. It is evident that TIS has a wide range of experimental possibilities, demonstrating that small-angle neutron scattering is one of the most informative structural methods for low resolution.