Joint use of SAXS and NMR

Annalisa Pastore

A common tool of Structural Biology is the use of a 'cut-and-paste' approach which consists in dissecting proteins in individual domains, study them separately and eventually combine the information to reconstruct the overall shape of a molecule. Nuclear magnetic resonance (NMR) and small angle X-ray scattering (SAXS) are complementary techniques which have individually proven their own merits. NMR gives structural information of relatively small portions of a molecule, while SAXS provides a description of the overall shape of even large molecules/molecular complexes. Here, I shall discuss a number of examples in which the two techniques may be used in combination. I shall discuss the successes as well as the still open problems and limitations of this approach. I shall for instance show how we have reconstructed the shape of a ternary complex between CyaY, the bacterial ortholog of the frataxin protein that is implicated in a hereditary ataxia and IscS/IscU, the two main components of the iron-sulfur cluster biogenesis. We fit the X-ray structures of the individual components into the SAXS density, while using NMR for mapping the surfaces of interaction. The resulting model was validated by specific mutations. Despite the evident success of our work, much more effort needs to be put to push the application of this approach further.

Date/time: Sunday, 21 October 2012, 15:00