Study of Multi Domain Protein Refinement By Different Types of Scattering Tools |
Determination of the 3Dstructures of multi domain proteins by solution NMR methods presents a numberof unique challenges related to their larger molecular size and the usualscarcity of constraints at the inter domain interface, often resulting in adecrease in structural accuracy. In this respect, experimental information fromsmall-angle scattering of X-ray radiation in solution (SAXS) presents asuitable complement to the NMR data, as it provides an independent constrainton the overall molecular shape. A computational procedure is described thatallows incorporation of such SAXS data into the mainstream high-resolutionmacromolecular structure refinement. The method is illustrated for a two-domain177-amino-acid protein, yS crystallin, using an experimental SAXS data setfitted at resolutions from ~200 A to ~30 A. Inclusion of these data duringstructure refinement decreases the backbone coordinate root-mean-squaredifference between the derived model and the high-resolution crystal structureof a 54% homologous yB crystallin from 1.96 ± 0.07 A to 1.31 ± 0.04 A.Combining SAXS data with NMR restraints can be accomplished at a moderatecomputational expense and is expected to become useful for multi domainproteins, multimeric assemblies, and tight macromolecular complexes..