Strukturelle und funktionelle Untersuchungen an Substratbindeproteinen aus ABC-Transportern zur Aufnahme von kompatiblen Solute

Abstract, publication of the main topic of the Dissertation: In the soil bacterium Bacillus subtilis, five transport systems work in concert to mediate the import of various compatible solutes that counteract the deleterious effects of increases in the osmolarity of the environment. Among these five systems, the ABC transporter OpuA, which catalyses the import of glycine betaine and proline betaine has been studied in detail in the past. Here, we demonstrate that OpuA is capable of importing the sulfobetaine dimethylsulfonioacetate (DMSA). Since OpuA is a classic ABC importer that relies on a substrate-binding protein priming the transporter with specificity and selectivity, we analyzed the OpuA-binding protein, OpuAC, by structural and mutational means with respect to DMSA binding. The determined crystal structures of OpuAC in complex with DMSA at 2.8 A resolution and a detailed mutational analysis of these residues revealed a hierarchy within the amino acids participating in substrate binding. This finding is different to other binding proteins that recognize compatible solutes. Furthermore important principles that enable OpuAC to specifically bind various compatible solutes were uncovered.