A resistant mutant of Plasmodium falciparum purine nucleoside phosphorylase uses wild-type neighbors to maintain parasite survival

Novel Dipeptide Inhibitors of PfPNP: In-Silico Identification of Promising New Antimalarials

Malaria, an infectious disease caused by Plasmodium falciparum, is becoming increasingly difficult to treat due to the emergence of drug-resistant strains. Recent studies have proposed purine nucleoside phosphorylase from P. falciparum (PfPNP) as a potential target for malaria treatment. In the present study, we designed a virtual library of 400 dipeptides to discover novel anti-malarial peptide inhibitors. A structure-based molecular docking method was employed to virtually screen the designed library against the wild-type structure of PfPNP (PDB: 5ZNC). The best four (Phe-Arg, Arg-His, Trp-Arg and Tyr-Arg) dipeptides, which were then investigated for their binding potential against PfPNP using Molecular Dynamics simulation studies. Parameters such as RMSD, RMSF, Rg, and SASA were analyzed to understand the structural changes, energetics, and overall behavior of PfPNP-dipeptide complexes. The PfPNP demonstrated significant stability upon binding with each of the identified dipeptides with ΔG of over -168 kcal/mol. Additionally, DFT and ADME predictions indicated that the electronic structure, energetics, and pharmacokinetic properties of Phe-Arg, Arg-His, Trp-Arg and Tyr-Arg were favourable for drug development. Our comprehensive computational investigation has identified these four dipeptides as promising candidates. These designed and selected dipeptides may further be modified using peptidomimetic and medicinal chemistry tools to develop a novel class of promising antimalarials.

Kinetic and Structural Characterization of Trypanosoma cruzi Hypoxanthine-Guanine-Xanthine Phosphoribosyltransferases and Repurposing of Transition-State Analogue Inhibitors

Over 70 million people are currently at risk of developing Chagas Disease (CD) infection, with more than 8 million people already infected worldwide. Current treatments are limited and innovative therapies are required. Trypanosoma cruzi, the etiological agent of CD, is a purine auxotroph that relies on phosphoribosyltransferases to salvage purine bases from their hosts for the formation of purine nucleoside monophosphates. Hypoxanthine-guanine-xanthine phosphoribosyltransferases (HGXPRTs) catalyze the salvage of 6-oxopurines and are promising targets for the treatment of CD. HGXPRTs catalyze the formation of inosine, guanosine, and xanthosine monophosphates from 5-phospho-d-ribose 1-pyrophosphate and the nucleobases hypoxanthine, guanine, and xanthine, respectively. T. cruzi possesses four HG(X)PRT isoforms. We previously reported the kinetic characterization and inhibition of two isoforms, TcHGPRTs, demonstrating their catalytic equivalence. Here, we characterize the two remaining isoforms, revealing nearly identical HGXPRT activities in vitro and identifying for the first time T. cruzi enzymes with XPRT activity, clarifying their previous annotation. TcHGXPRT follows an ordered kinetic mechanism with a postchemistry event as the rate-limiting step(s) of catalysis. Its crystallographic structures reveal implications for catalysis and substrate specificity. A set of transition-state analogue inhibitors (TSAIs) initially developed to target the malarial orthologue were re-evaluated, with the most potent compound binding to TcHGXPRT with nanomolar affinity, validating the repurposing of TSAIs to expedite the discovery of lead compounds against orthologous enzymes. We identified mechanistic and structural features that can be exploited in the optimization of inhibitors effective against TcHGPRT and TcHGXPRT concomitantly, which is an important feature when targeting essential enzymes with overlapping activities.

2-Methylthio-N7-methyl-cis-zeatin, a new antimalarial natural product isolated from a Streptomyces culture

2-Methylthio-N7-methyl-cis-zeatin (1) was isolated from the culture broth of Streptomyces sp. 80H647 along with 2 known purine derivatives, 5'-methylthioinosine (2) and AT-265 (dealanylascamycin, 3). The structure elucidation of compound 1 was accomplished by high-resolution mass spectrometry (HRMS) and nuclear magnetic resonance (NMR) analyses. It inhibited the growth of Plasmodium falciparum 3D7 with a GI50 of 2.4 µm and had no effect on the growth of Arabidopsis at 2 µm. This is the first report of an N7-methylated zeatin-type natural product from Streptomyces and as an antimalarial compound.

Plasmodium falciparum finds the winning combination

After 3 years of laboratory drug pressure in the presence of a picomolar inhibitor, the parasite Plasmodium falciparum developed a combination strategy of gene amplification and mutation to regain viability. The mutation observed led to a dysfunctional enzyme, but new research reveals the clever mechanism behind its success. Not that we needed a reminder of nature's creativity in the time of a pandemic.