Probing Allosteric Inhibition and Activation of Acinetobacter baumannii ATP Phosphoribosyltransferase.

Antimicrobial resistance is on the rise. This global threat is predicted to claim more lives than cancer by 2050 if not properly addressed. We urgently need novel drugs that affect new molecular targets. More than that, we need different strategies to develop more effective antibiotics against pathogenic bacteria. Broad-spectrum antibiotics are indispensable in cases of acute infections where a diagnosis is missing. However, they have the disadvantage of adding undue selective pressure against most bacteria in the body, which favours the proliferation of drug-resistant strains of non-pathogenic bacteria. By several mechanisms of horizontal gene transfer, the genes or plasmids conferring resistance may, in time, end up in pathogenic species.
In cases of chronic or recurrent infections and hospital-associated infections (HAIs), which are often accompanied by a diagnosis of the bacterial species responsible for the disease, narrow-spectrum antibiotics are ideal. This is because they will target only that species, avoiding selective pressure on other bacteria. This strategy will increase the (useful) lifespan of the drug, preserve the healthy microbiota, and ultimately help reduce the spread of antimicrobial resistance. The development of narrow-spectrum antibiotics requires identification and in-depth mechanistic knowledge of suitable molecular targets.
Acinetobacter baumannii is a Gram-negative nosocomial pathogen whose proliferation of antimicrobial resistance strains prompted the WHO to place it as the most critical bacterium against which novel antibiotics are needed. It often causes HAIs and recurrent infections, usually pneumonia. The characterisation of uniquely validated molecular targets in A. baumannii will aid the development of efficient narrow-spectrum antibiotics against this species. The key factors responsible for antimicrobial resistance in A. baumannii are its ability to form biofilms and its capacity to persist in the lungs.
The first enzyme of histidine biosynthesis in A. baumannii is an attractive validated target for drug development. ATP phosphoribosyltransferase (ATPPRT) is a short-form, hetero-octameric ATPPRT made up of two different proteins: HisGS, the catalytic subunit, and HisZ, a regulatory subunit that allosterically activates catalysis by HisGS and mediates its allosteric inhibition through histidine binding. Specifically, in A. baumannii, HisZ has been shown to be essential for growth even in rich medium, which suggests that regulation of this highly energy-consuming pathway is of paramount importance. Intriguingly, HisGS is not essential for growth in rich medium, but is required, along with several other histidine biosynthesis enzymes, for A. baumannii to persist in the lungs during pneumonia. Thus, disrupting HisZ function (e.g. with allosteric activators) will halt bacterial growth, while inhibiting HisGS will prevent persistence in the lung during pneumonia.
Accordingly, this project will employ experimental and computational approaches to:
Dissect the molecular, atomic, and dynamic basis for ATPPRT allosteric inhibition by histidine;
Discover/develop allosteric activators ATPPRT and elucidate their mechanism of action;
Discover/develop allosteric and/or orthosteric inhibitors of ATPPRT and elucidate their mechanism of action.