Seminars Archive

Structural investigations in the colloidal domain: SAXS to study proteins in solution and self-assembled nanoaggregates

Alessandra Del Giudice
Department of Chemistry, Sapienza University of Rome

Abstract
At the intermediate length scale between typical atomic distances within a molecule and macroscopic sizes of materials (1-100 nm) interesting phenomena occur guided by intermolecular interactions and on energetic scales comparable with thermal fluctuations: we are in the “colloidal” and “soft matter” domain, to which many familiar systems belong, including everyday use formulations and the molecular constituents of life.
Small angle X-ray scattering (SAXS) can be a valuable tool to study the structure of such systems and the changes occurring as a function of stimuli and perturbations, thanks to the averaged structural insight on an extended interval of length scales and the applicability in conditions that can be close to the functional state or modified in a controlled way to study structural responses.
In the case of biological macromolecules and particularly for proteins, SAXS can monitor phenomena like conformational variations and complex formation, possibly implicated in physiologically important mechanisms.
Considering smaller building blocks, SAXS can “see” self-assembly phenomena of amphiphilic molecules in supramolecular aggregates, and help understanding their variability as a function of several parameters, given the multiplex nature of the involved interactions.
In this context, examples of structural investigations in solutions will be shown. We will focus on the conformational changes of albumin, the most abundant transporter protein of body fluids, and on the complex self-assembly of sodium deoxycholate, a natural facial amphiphile belonging to the bile salt family.