The structural biology of FabG proteins from multidrug-resistant Acinetobacter baumannii

Cross EM, Smith KM and Forwood JK

Charles Sturt University Wagga Wagga NSW 2678.

Acinetobacter baumannii is a gram negative, nosocomial pathogen that is resistant to multiple drug classes, including carbapenems. In 2017, the World Health Organisation listed A. baumannii as priority one for the research and development of new antibiotics. Fatty acids are essential cell components, required for formation of phospholipids, lipopolysaccharides, and lipoproteins that help build the bacterial cell envelope. Bacterial type two fatty acid synthesis (FASII), is a potential target for the development of inhibitors and is favourable due to the distinct differences from eukaryotic type one fatty acid synthesis (FASI). In particular the first reductase enzyme, 3-oxoacyl-ACP reductase (FabG), is an attractive target for inhibition in the FASII pathway. FabG is a member of the short-chain dehydrogenase/reductase family, a class of proteins known to display a diverse range of functions whilst maintaining conserved sequence motifs and typical Rossmann folding patterns. BLAST results show multiple sequences annotated as FabG proteins for A. baumannii, which has been noted in other bacteria such as Mycobacterium tuberculosis and suggested to play a role in bacterial virulence. This project aims to find the structure of FabG homologs through recombinant protein expression, purification and crystallization. Diffraction data was collected at the Australian Synchrotron and used to solve the enzyme structure. The structural analysis was complemented with functional data, enabling the assessment of enzyme activity against different substrates. This was achieved spectrophotometrically by analysing the oxidation of the cofactor (either NADH or NADPH) and observing a decrease in absorbance at 340nm. Inhibitors designed to target FabG proteins and prevent fatty acid synthesis are currently under investigation, and may provide a platform for the potential use against multidrug-resistant Acinetobacter baumannii.