Satya successfully defended her PhD at Jacobs University on May 17th, 2017.
“Structure-function relation and transport across Gram-negative outer membrane channels investigated by Electrophysiology”.
The outer membrane (OM) of Gram-negative bacteria contains channels involved in small molecule uptake and information exchange. Based on the energy used for the molecular transport, these channels are classified as passive diffusion channels and active transporters. For selective uptake of molecules throughtranslocation, channels display various structural features such as long extracellular loops, residue constellations near their constriction region and various periplasmic N-terminus extensions.
This thesis focusses on two main concepts: the structure-function relationship of OM channels and the translocation of molecules through these channels. For the investigated passive diffusion channels and active transporters, the role of N-termini in their structure-function relationship was studied using electrophysiology. Furthermore,translocation was probed for both charged and uncharged molecules.
The existence and role of electro-osmosis in substratetranslocation is the most exciting result, along with the gating behaviour of the N-terminus of the uncharged cyclodextrin specific channel CymA from Klebsiella oxytoca. Moreover, the electro-osmosis phenomenon is not bound to this specific channel.
For the putative channel DcaP from Acinetobacter baumannii, its existence as a trimeric channel and exclusive anion selectivity was revealed. It possesses a long N-terminus and its role in the uptake of charged dicarboxylic acids was established.
For the SusCD protein complex involved in the glycan metabolism of human gut bacteria, the role of N-terminus as a plug, occluding the SusC transporter was established. The structure-function relation between two interacting proteins was also elucidated and coined as pedal-bin mechanism.
For the efflux protein OM component TolC, its channel opening was explained at extreme applied voltages.
Overall, the results of my doctoral study encompass conclusions on the role of N-termini, the presence and role of electro-osmosis, the uptake of charged dicarboxylic acids, a novel mechanism for inter-protein interactions, and even on channel opening mechanisms.