Open Access

Satya Prathyusha Bhamidimarri

• The outer membrane (OM) of Gram-negative bacteria contains channels involved in small molecule uptake. Based on the energy used for the molecular transport, these channels are classified as passive diffusion channels and active transporters. For selective molecular uptake, channels display various structural features such as long extracellular loops, residue constellations near constriction region and various N-terminus extensions.This thesis focuses on two main concepts: the structure-function relation of OM channels and the associated transport. For the investigated passive diffusion channels and active transporters, the role of N-termini in their structure-function relation was studied using electrophysiology. Furthermore, translocation was probed for both charged and uncharged molecules. The existence and role of electro-osmosis in substrate translocation 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, the role of which 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 in SusC transporter was established. Pedal- bin mechanism of the two interacting proteins was also elucidated. 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.