Analysis of models of irregular shape by solution X-ray scattering: the case of the 50S ribosomal subunit from E. coli.

Structural models of biological macromolecules can be tested by comparing calculated and experimental solution scattering curves. We have developed an approach for computing scattering shape functions at medium resolution from models proposed on the basis of other techniques such as electron microscopy. We present the results obtained with the 50S ribosomal subunit from Escherichia coli; two models are considered, one proposed by Lake (1976), the other one by Tischendorf et al. (1975). Although the two models are similar in many respects, their scattering shape functions are significantly different. The comparison with the experimental scattering curve allows us to check the scale of the models and, after scaling, to quantitate the agreement between the observed and the calculated curves. Finally, it can provide a starting point for the structural interpretation of the X-ray data.