ИСТИНА

Formation of bio-crystals by living organisms (bacteria, viruses, cells) is one of the most intriguing processes of life sciences at the moment. Protein crystallization in living cells occurs as a native process under stress conditions. The universal mechanism of response to stress for E. coli and other bacteria is their transition to the stationary phase. In this phase, there is a sharp increase of intracellular synthesis of specific histone-like Dps protein that binds DNA to protect the genome against deleterious factors. Formation of the Dps/DNA complex leads to in cellulo crystallization. The protein crystallization in living cells enables the growth of a large number of high-quality crystals in short time that can be used to extract high-resolution structural information by applying serial X-ray crystallography. However, the small size and the sometimes low percentage of crystal containing cells within a culture limit the use of the method. On the other hand, the application of the high throughput small-angle X-ray scattering (SAXS) technology allows not only an ability to quickly detect the presence of crystals in living cell culture but also makes it possible to qualitatively evaluate crystal types within cells, based on the presence of defined Bragg peaks in the scattering profile. This is especially important since a structural aspect of the phenomenon is still unclear, and there is a great deal of uncertainty regarding the actual structure of the Dps-DNA cocrystals both in cells and in vitro – no hypothesis was backed up with any direct methods. In the present study we applied SAXS to analyze and visualize Dps-DNA co-crystals formation in cellulo and in vitro. Our findings detected significant differences and peculiarities of crystallization processes in living cells and in solution. Relevant structural models and hypotheses were considered. This work was supported by the Russian Science Foundation (project No. 18-74-10071).