PhD ceremony Ms. N. Gul: Expression and functional characterization of membrane proteins

PhD ceremony: Ms. N. Gul, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Expression and functional characterization of membrane proteins

Promotor(s): prof. B. Poolman

Faculty: Mathematics and Natural Sciences

Nadia Gul has focused on the production and functional analysis of membrane proteins. She developed a method to select for Escherichia coli strains that express (membrane) proteins at an elevated level and in a functional state. This method is important for production and study of difficult to express proteins such as transporters and receptors. These proteins are of tremendous biotechnological and pharmaceutical importance. Gul even filed a patent on the procedure and the newly developed expression hosts.

Membrane proteins mediate and control transmembrane transport and signaling and thus perform variety of physiological functions including nutrient uptake, waste excretion, energy and signal transduction. The low natural expression and hydrophobic nature of membrane proteins complicates their study. Producing correctly-folded membrane proteins and analyzing their functions in native and synthetic membranes are key-challenges in the field of membrane biology.

In the study of Gul E. coli was evolved and strains were selected that produced enhanced levels of correctly folded protein. Each of the evolved strains was sequenced and the remarkable finding was made that each of the better-producing strains had a mutation in hns, a gene encoding a general transcription factor. The H-NS protein also plays a role in the organization of the chromosome In addition to hns, each of the evolved strains carries one or two more mutations that may have contributed to the improved performance of the strains.

Gul also describes the purification and functional reconstitution of the ATP-binding cassette transporter ProU, an important membrane protein that plays in a role in the regulation of the volume of E. coli cells. She established the gating conditions of ProU in membrane model systems. Moreover, Gul performed function-structure studies on another member of the family of osmoregulatory ABC transporters, namely OpuA. This protein has the unique property of having an amphipathic α-helix associated with the transmembrane domain. Gul anticipated that it might play a role in the osmotic regulation of transport. She showed that the amphipathic α-helix is required for full transporter activity but does not have a regulatory role. I also determined that the amphipathic α-helix is located close to the membrane surface.