On the transport mechanism of energy-coupling factor transporters

Energy-coupling factor (ECF) transporters are membrane proteins that mediate the uptake of vitamins in prokaryotes, among which many pathogenic bacteria. However, ECF transporters have not been identified in humans. This thesis focusses on substrate binding of vitamins to the substrate binding domain (S-component) of these transporters, and the subsequent transport carried out by the complete ECF transporter. In the first part of the thesis, the method of structural-based design of thiamin derivatives was used to get more insight in which functional groups of thiamin (vitamin B1) and which residues of the thiamine-specific S-component ThiT are important for the strong binding of thiamine to ThiT. The second part starts with a new working model of the transport mechanism of ECF transporters, which was proposed after solving two crystal structures of the ECF transporter for folate (vitamin B11) and one of its S-component in the folate-bound state. Subsequently, an updated version of the working model is presented after obtaining data on the dissociation of the S-component from the transporter complex. Finally, the identification of an inhibitor of the ECF transporters from the organism Lactobacillus delbrueckii is described. This inhibitor could lock the ECF transporters in a certain state of the transport cycle, what could result in more insight in the transport mechanism of the ECF transporters, but what could also be a first step in the development of a new type of antibiotics against pathogenic bacteria that rely on ECF transporters for their vitamin uptake.