Octamers participation in the formation of lysozyme ordered layers from crystallization solutions

Abstract The results of the study of thin film ordered protein structures formed from polydisperse solutions of lysozyme using Langmuir technology are presented. The proposed method for producing protein films is based on a modification of the Langmuir-Schaeffer method, which consists in using a pre-prepared protein solution with the addition of a precipitant. The pre-prepared protein solutions’ parameters (protein and precipitant concentrations, buffer type, etc.) correspond to protein crystallization conditions. It is assumed that protein oligomers formed in the solution as a result of the addition of the precipitant (in particular, for lysozyme these oligomers include octamers) are directly involved in the formation of Langmuir protein layers on the surface of the liquid and on solid substrates. Using the method of grazing-incidence X-ray standing waves, the structure of multilayered protein systems formed from polydisperse solutions was studied, which made it possible to determine directly the position of precipitant ions (NaCl, CuCl2 and NiCl2) relative to the protein layer. The method of processing the X-ray reflectivity and grazing-incidence X-ray standing waves data, based on the use of information on the atomic structure of lysozyme octamers isolated from the crystal lattice, made it possible to determine the thickness and electron density of protein films and to reveal the orientation of protein molecules in the layer.