GbsR Typ Regulatoren: Charakterisierung einer neuen MarR-Typ Regulator Familie von transkriptionellen Repressoren

To protect itself against osmotic stress the soil bacterium Bacillus subtilis accumulates compatible solutes in the cell. One of the most important compatible solutes is glycine betaine. This osmoprotective substance can either be absorbed through the Opu transporters of the cell or can be synthesized from the precursor molecule choline. The oxidation of choline takes place via the two dehydrogenases GbsB and GbsA which are present in the genome of B. subtilis organized as an operon. Next to the operon is the gene gbsR that encodes the choline sensitive repressor GbsR. GbsR regulates the expression of the gbsAB operon and the opuB operon coding for the choline specific ABC transporter. If it is choline in the cell, it binds to the regultor GbsR. This detaches from the DNA and the two operons can be expressed. The regulator GbsR from B. subtilis has become aware of a new class of MarR type regulators (Nau-Wagner et al., 2012). The type of GbsR regulators family was characterized in this work in more detail. GbsR type regulators are disseminated both in the domain of Bacteria and Archaea. The GbsR type regulators regulate the osmotic-dependent genes occur mainly in Firmicutes. The regulators can be divided into two groups based on their genomic neighbourhood. The transporter and the synthesis class. GbsR type regulators from the transporter class regulate the expression of ABC transporters of compatible solutes. Regulators of synthesis class repress genes for the glycine betaine synthesis. For the regulation of each adjacent operons GbsR type regulators binds on a palindromic bindingmotiv. Upon binding of DNA, the GbsR type regulators used the conserved winged helix motif. Regulators of the transporter class bind at the 35 region of the promoter of the adjacent gene. The GbsR type regulators of synthesis class bind as "roadblock" downstream of the transcription start. GbsR type regulators regulate not only the adjacent operon. They are responsible in part for the regulation of several osmotic dependent genes. Using the example of opuB operon of B. subtilis, a regulatory model could be created on which two GbsR type regulators are involved. GbsR type regulators bind compatible solutes over cation-π interaction in a ligand binding pocket, which probably consists of several amino acids. GbsR type regulators of synthesis class seem to be able to exclusively bind choline, regulators of transportation class contrast several different compatible solutes. The composition of the amino acids that make up the ligand binding pocket, it seems decisive for the range of compatible solutes that can be bound. Specifically, the opu regulon from the marine Bacillus infantis NRRL B 14911 could be characterized. Also a model of regulation of opuA operon could be proposed. The OpuA transporter contained in the gene cluster transports the same compatible solutes such OpuA from B. subtilis. They are used by the marine bacterium B. infantis NRRL B 14911 as osmoprotektiva.