As part of our continued investigation for novel architectures for drug discovery, here at Newcastle we have access to large libraries of compounds via our high throughput screening facility. As such we are beginning to focus on the testing and identification of novel architectures to develop and translate as new antibacterials in the treatment of infectious diseases.
PabB (aminodeoxychorismate synthase) is an enzyme that catalyzes the chemical reaction of chorismate and glutamine to produce 4-amino-4-deoxychorismate and glutamate. Specifically, aminodeoxychorismate synthase is a transaminase that transfers an amino group to a keto acid. Formerly aminodeoxychorismate synthase was referred to as PABA synthase; however this name is no longer recommended[5] as it is understood that the formation of PABA requires the action of a further enzyme, 4-amino-4-eoxychorismate lyase.
In certain microbial species such as Escherichia coli, aminodeoxychorismate synthase is a heterodimeric complex composed of two proteins, glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB). In Escherichia coli, the reaction is a two step process. Glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB) form a heterodimeric complex that catalyzes the synthesis of 4-amino-4-deoxychorismate. The first step occurs with PabA abstracting ammonia from glutamine. The second step occurs when PabB reacts both substrates (chorismate and ammonia) to synthesize 4-amino-4-deoxychorismate (Figure 1).
Figure 1: Biosynthetic pathway and inhibitor AbyssomicinC
As part of our programme, we have worked with Ersilia (Open Source AI organisation) to generate an in silico validated library of compounds which have been assessed further to provide the 100 best compounds for further study. Here we are working to synthesise the substrates for testing to see if we can identify a novel, efficacious small moleculePabB binder for further exploitation.
In this project we have developed a new architecture with three structural components being, a hydrazine, amino acid and a coupled reagent (Figure 1A). This combination has produced a series of novel benzoxa-[2,1,3]-diazole substituted amino acid hydrazides 1, as selective drugs for the treatment of TB, highlighting the importance of the benzo-[2,1,3]-diazole, amino acid (AA) and the substituted aryl hydrazine (R1), towards Mtb selectivity, potency, efficacy, and avoidance of toxicity against mammalian cells.
Notwithstanding this, further work has shown that structural variance of this architecture and recombination with diverse hydrazines, natural amino acids and N-backbone substitution enables a wide range of structure-activity relationships to be obtained 2, 3 (Figure 1B).
Figure 1: A.) Shows the variability in the molecule and sites for modification; B.) N-substituted amino acid hydrazide molecules and their associated inhibitory activity.
In furtherance of our initial findings with benzoxa-[2,1,3]-diazole substituted amino acid hydrazide moieties 1 we undertook mutant generation from our lead molecule, sequencing of the mutated bacteria and subsequent bioinformatics analysis that revealed a new, novel, uncharacterised protein Rv1543. Subsequently, this target has been implicated in the electron transport chain plays a role in the menaquinone pathway and is critical for Mtb survival. Current work is focused on determining the role of this protein in Mycobacterium tuberculosis with structure-based drug design to follow in the future.
Biosciences Institute
Faculty of Medical Sciences
Newcastle University
Cookson Building
Newcastle-upon-Tyne
NE2 4HH, UK
Tel.: +44 (191) 2082357
Email: jon.sellars@newcastle.ac.uk
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