Diamond Annual Review 2023/24

16 D I A M O N D L I G H T S O U R C E A N N U A L R E V I E W 2 0 2 3 / 2 4 Tuberculosis breakthrough should lead to a new range of anti-TB inhibitors Tuberculosis (TB) is one of the deadliest infectious diseases worldwide that is spread in the air like the common cold. During infection the TB bacteria Mycobacterium tuberculosis (Mtb) can utilise lipids (cholesterol and fatty acids) from the human host to act as nutrients to maintain and fuel the infectious state. Drug resistant TB strains are spreading and present a major concern. A team of scientists from Manchester, Cambridge and Huddersfield Universities used a structure-guided approach, combined with biophysical characterisation to obtain a series of compounds with activity against clinically relevant drug-resistant isolates. They studied a set of enzymes involved in a key step in the breakdown of host cholesterol used by the TB bacteria. Their work involves characterising the enzymes using the UK’s national synchrotron, Diamond Light Source X-ray macromolecular crystallography beamlines to view their structures inmolecular detail. These enzyme structures are used to design inhibitor molecules that can bind to the enzymes and prevent them doing their job - essential for TB infection. The inhibitors molecules initially came from screening a library of small chemical compounds and were then gradually built up and synthesised chemically designing them to sit specifically into the enzyme structure. The leading compounds were tested against clinically active and drug resistant strains of Mycobacterium tuberculosis and revealed anti-TB activity. With the emergence of extensive drug resistance, novel therapeutic agents are urgently needed, and continued drug discovery efforts required. Mtb cytochrome P450 (CYP) enzymes facilitate key steps in cholesterol catabolism and thus present potential targets for inhibition. The authors present a series of compounds based on an ethyl 5-(pyridin-4-yl)- 1H-indole-2-carboxylate pharmacophore which bind strongly to both Mtb cholesterol oxidases CYP125 and CYP142. Katariya, M. M. et al. DOI: 10.1002/chem.202203868 MX Science Highlights Figure: The synthetic expansion of a chemical structure in two directions designed to fit into the active site of Mtb cholesterol oxidase enzymes to generate a new range of inhibitors and potential anti-TB drugs. The right-hand image shows a close-up of the x-ray crystal structure of the Mtb CYP125 enzyme bound to one of the leading inhibitor compounds. Credits: University of Huddersfield Deciphering the sugar transport in plants In most plant species, sucrose is the main form of assimilated carbon produced during photosynthesis. Sucrose is essential for plant growth, as it provides a source of carbon to produce new molecules, but also energy for the plant cells. Sucrose has also an associated role as a signalling molecule, by regulating the growth of new organs, accumulation of storage proteins, and flowering in plants. Despite their key role in plants, the working mechanism of these SUCs transporters is not yet well understood. A team of researchers from the Aarhus University recently published a new study to understand the precise mechanism of action of the SUC1 transporter. They used X-ray diffraction data collected at I04 and I24 beamlines at Diamond to determine the 3D structure of this transmembrane protein. They wanted to understand how SUCs protein recognise sucrose, and how transport is proton coupled. The researchers present the structure of SUC1, and key elements to explain both the recognition of sucrose by the transporter, and the active transport by proton coupling. The SUC1 activity is using the proto-motive force to function. As such, it requires an acidic amino acid in the transmembrane domains. The authors showed that the protein possessed only one amino acid that is consistent with this description (the aspartate located at position 152). The research done by this team is important, as it highlights a major process in plants. Sucrose has many functions in plants, understanding how the transport is done is a first step to decipher more complex interactions between sucrose and regulatory pathways. Bavnhøj, L. et al. DOI :10.1038/s41477-023-01421-0 Figure: a) The 2.7 Å electron density map of SUC1 (2mFo-DFc map contoured at 1σ). Density corresponding to the N and C domain are coloured cyan and orange, respectively. EHR and IHR domains are coloured pale yellow. b, Side view of the structure of SUC1 in the plane of the plasma membrane. Bottom, a top view from the extracellular side with M1–M12 labelled. d, Topology of SUC1. Disordered N-terminal (residues 1–24) and C-terminal (residues 501–513) ends are shown as dashes. Nature Plants (Nat. Plants) ISSN 2055-0278 (online)