STUDYING PROTEIN SOLUTIONS BY SYNCHROTRON SAXS: FROM STATIC TO RAPID MIXING KINETIC EXPERIMENTS

Small Angle X-Ray Scattering (SAXS) is a widely used and well-established technique for structural studies, from hard to soft and biological matter. In recent years, significant progress have been made in terms of data analysis methods and instrumentation, especially for 4th generation synchrotron machines, with a wide range of sample environments and experimental conditions available. One of the main types of sample studied by SAXS is proteins, or protein-interacting systems, such as protein-surfactant and protein-nanoparticle mixtures. The aim of this work is to illustrate different studies performed on protein samples using synchrotron SAXS. Molecular chaperones are a class of proteins difficult to crystallize and their structure is very dynamic in nature, so solution SAXS is especially useful for their studies. Here we show the modelling of chaperones to illustrate different analysis methods. We also show a case of protein-membrane interactions: hHep1 is a co-chaperone of mortalin, the mitochondrial Hsp70, and there is little information regarding its interaction with the membrane. SAXS shows this interaction as being more superficial by using liposomes as biomimetic system, with the data indicating that hHep1 docks to the liposome without penetrating deep into the bilayer. We present examples of SAXS with stopped-flow rapid-mixing, especially useful for probing self-assembly pathways, such as virus capsid assembly. We hope that this this presentation illustrates the current capabilities of SAXS for researchers interested in structural studies of protein systems.

This work was supported by the ESRF, PSCM, CNPq (200024/2023-0), CAPES (88887.694557/2022-00) and FAPESP (2017/26131-5).