The gut microbiota, its relationship to the immune system, and possibilities of its modulation.

Research of the gut microbiota allows a better understanding of its composition and function and reveals the links between changes in the composition of bacteria and various intestinal but also systemic diseases. The gut microbiota performs several of important functions in the host body and influences many physiological processes. Gut bacteria synthesize many compounds needed for the proper function of the body (e.g., vitamins, short-chain fatty acids, and amino acids). They help maintain the integrity of the intestinal barrier and protect against pathogens. The gut microbiota plays a crucial role in the development and function of the immune system. Significant changes in the composition of the intestinal microbiota led to a dysbiotic state and the loss of its beneficial functions for humans. The review article summarizes the basic knowledge about the composition and function of the bacterial gut microbiota in healthy people, its role in the development of the immune system, and the mechanisms involved in maintaining homeostasis. It also presents current knowledge about the possibility of targeted modulation of the bacterial gut microbiota and faecal transplantation.

Three-dimensional reconstruction of the S885A mutant of human mitochondrial Lon protease.

The Lon protein is a protease belonging to the superfamily of ATPases associated with diverse cellular activities (AAA+). Its main function is the control of protein quality and the maintenance of proteostasis by degradation of misfolded and damaged proteins, which occur in response to numerous stress conditions. It also participates in the regulation of levels of transcription factors that control pathogenesis, development and stress response. We focus our interest on the structure of human mitochondrial Lon (hLon) protease, whose altered expression levels are linked to some severe diseases such as epilepsy, myopathy, or lateral sclerosis. We present the first 3D structure of the ADP-bound human Lon S885A mutant obtained by electron microscopy as a result of preliminary negative staining studies. S885A appears as a hexameric ring of 120 Å diameter having 90 Å in height. Its resolution was estimated at 19 Å by the FSC = 0.5 criterion. This model is a primary step towards the understanding of the mechanism of action of the Lon protease and its involvement in the pathogenesis development.

The influence of ATP-dependent proteases on a variety of nucleoid-associated processes.

ATP-dependent proteases are crucial components of all living cells and are involved in a variety of responses to physiological and environmental changes. Nucleoids are dynamic nucleoprotein complexes present in bacteria and eukaryotic organelles (mitochondria and plastids) and are the place where the majority of cellular responses to stress begin. These structures are actively remodeled in reaction to changing environmental and physiological conditions. The levels of nucleoid protein components (e.g. DNA-stabilizing proteins, transcription factors, replication proteins) therefore have to be continually regulated. ATP-dependent proteases have all the characteristics needed to fulfill this requirement. Some of them bind nucleic acids, but above all, they control and maintain the level of many DNA-binding proteins. In this review we will discuss the roles of the Lon, ClpAP, ClpXP, HslUV and FtsH proteases in the maintenance, stability, transcription and repair of DNA in eubacterial and mitochondrial nucleoids.