Ambiguities and completeness of SAS data analysis: investigations of apoferritin by SAXS/SANS EID and SEC-SAXS methods

The method of small angle scattering (SAS) is widely used in the field of biophysical research of proteins in aqueous solutions. Obtaining low-resolution structure of proteins is still a highly valuable method despite the advances in high-resolution methods such as X-ray diffraction, cryo-EM etc. SAS offers the unique possibility to obtain structural information under conditions close to those of functional assays, i.e. in solution, without different additives, in the mg/mL concentration range. SAS method has a long history, but there are still many uncertainties related to data treatment. We compared 1D SAS profiles of apoferritin obtained by X-ray diffraction (XRD) and SAS methods. It is shown that SAS curves for X-ray diffraction crystallographic structure of apoferritin differ more significantly than it might be expected due to the resolution of the SAS instrument. Extrapolation to infinite dilution (EID) method does not sufficiently exclude dimerization and oligomerization effects and therefore could not guarantee total absence of dimers account in the final SAS curve. In this study, we show that EID SAXS, EID SANS and SEC-SAXS methods give complementary results and when they are used all together, it allows obtaining the most accurate results and high confidence from SAS data analysis of proteins

Photo-voltage of highly-oriented bacteriorhodopsin in purple membranes: Possibilities for bio solar cells

Highly oriented purple-membrane films of bacteriorhodopsin were obtained using external electrical field between two ITO (Indium Tin Oxide) supports. Purple membrane films, highly oriented in one direction showed 300 mV of photo-voltage while being illuminated by cold light lamp. Concentration of bacteriorhodopsin in purple membranes (bR in PM) and salt concentration were screened in order to find optimal conditions for maximizing the photo-voltage. The dependence of electrical properties of the films from light irradiation was investigated. Results obtained in this work might be important for optogenetic tools and for creating bio solar cells based on photosensitive membrane proteins