INORGANIC IONS INFLUENCE ON STRUCTURE OF SOLUTION OF HUMAN SERUM ALBUMIN

Andrey Goryunov¹, Svetlana Mokeeva², Valentina Petrova¹

¹Institute of Biology, Karelian Research Center, 11 Pushkinskaya st, 185610, Petrozavodsk, Russia
²KFFT, Petrozavodsk State University, pr. Lenina 33, 185640, Petrozavodsk, Russia,
E-mail: mokeeva@mainpgu.karelia.ru.

Keywords: small-angle scattering, protein solution, human serum albumin

There is increasing evidence of precise physical methods that globular protein molecules can build up clusters or microcoacervates even in diluted solutions which structural organization is thus revealed. However the regularities of forming of supramolecular structures in globular protein solution especially under moderate and increased salt concentrations, stay not enough studied despite its importance for understanding of a protein folding and stability, biological and medical significance.

The effect of inorganic ions (NaCl) on dispersion of human serum albumin solution was studied in the present work using X-ray small-angle scattering method. The curve of angular distributions of the X-ray scattering intensity at small angles for human serum albumin solution have been obtained at protein concentrations of 160, 120, 50 mg/ml and at NaCl concentrations in solvent of 0.0, 0.01M, 0.1M, 1M. The form of the scattering curve indicates that solutions are polydispers systems, i.e. there is a protein particles size distribution. The size interval is 1.5 - 5.5 nm. It means that the particles exceed the protein molecules in size (3 nm). When the salt concentrations was increased within the range of 0.0 - 0.1M the scattering intensity was invariable in spite of a reduction of the difference between protein and solvent electron densities. At the transition from NaCl moderate concentrations (0,1M) to increased ones (1M) the scattered intensity greatly decreases. The shape of the scattering curves for the maximum salt concentration differs substantially from scattering curves at smaller concentrations, that points to changing of protein size distributions. This result confirms our recent EPR spin-label data about the changing of degree of protein molecules association to clusters within the range of moderate salt concentrations.