Biology subjects

Shami, G. J.

Publications and source records attributed to Shami, G. J..

4 recordsLinked to original sources

bioRxiv2025

Natural product-mediated reaction hijacking mechanism validates Plasmodium aspartyl-tRNA synthetase as an antimalarial drug target

Malaria poses an enormous threat to human health. With ever-increasing resistance to currently deployed antimalarials, new targets and starting point compounds with novel mechanisms of action need to be identified. Here, we explore the antimalarial activity of the Streptomyces sp natural product, 5'-O-sulfamoyl-2-chloroadenosine (dealanylascamycin, DACM) and compare it with the synthetic adenosine monophosphate (AMP) mimic, 5-O-sulfamoyladenosine (AMS). These nucleoside sulfamates exhibit potent inhibition of P. falciparum growth with an efficacy comparable to that of the current front-line antimalarial dihydroartemisinin. Exposure of P. falciparum to DACM leads to inhibition of protein translation, driven by eIF2 phosphorylation. We show that DACM targets multiple amino acyl tRNA synthetase (aaRS) targets, including the cytoplasmic aspartyl tRNA synthetase (AspRS). The mechanism involves hijacking of the reaction product, leading to the formation of a tightly bound inhibitory amino acid-sulfamate conjugate. We show that recombinant P. falciparum and P. vivax AspRS are susceptible to hijacking by DACM and AMS, generating Asp-DACM and Asp-AMS adducts that stabilize these proteins. By contrast, human AspRS appears less susceptible to hijacking. X-ray crystallography reveals that apo P. vivax AspRS exhibits a stabilized flipping loop over the active site that is poised to bind substrates. By contrast, human AspRS exhibits disorder in an extended region around the flexible flipping loop as well as in a loop in motif II. These structural differences may underpin the decreased susceptibility of human AspRS to reaction-hijacking by DACM and AMS. Our work reveals Plasmodium AspRS as a promising antimalarial target and highlights structural features that underpin differences in the susceptibility of aaRSs to reaction hijacking inhibition.

biochemistry↗

bioRxiv2023

The Plasmodium falciparum artemisinin resistance-associated protein Kelch 13 is required for formation of normal cytostomes

Artemisinin (ART) is a quick-killing and effective antimalarial activated by the haem derived from haemoglobin digestion. Mutations in the parasites Kelch 13 (K13) protein compromise the efficacy of this drug. Recent studies indicate an undefined role for K13 in haemoglobin uptake. Here, we show that K13 is associated with the collar that constricts cytostomal invaginations required for the parasite to ingest host cytosol. Induced mislocalisation of K13 led to the formation of atypical invaginations lacking the cytostomal ring and constricted neck normally associated with cytostomes. Moreover, the levels of haemoglobin degradation products, haem and haemozoin, are decreased when K13 is inactivated. Our findings demonstrate that K13 is required for normal formation and/or stabilisation of the cytostome, and thereby the parasites uptake of haemoglobin. This is consistent with perturbation of K13 function leading to decreased activation of ART and consequently, reduced killing. Significance StatementArtemisinin-resistant parasites contain mutations in the gene encoding the Kelch 13 protein (K13). How K13 mutations result in artemisinin resistance is unclear. Here, we present evidence that normal K13 is required for the formation of the cytostome, a specialised parasite feeding apparatus used to endocytose host cell haemoglobin. Our results suggest that artemisinin resistance is due to a decrease in artemisinin activation brought about by a decrease in efficiency of haemoglobin uptake and consequently reduced production of haem.

microbiology↗

bioRxiv2021

Virulence determinant, PTP7, controls vesicle budding from the Maurers clefts, adhesin protein trafficking and host cell remodeling in Plasmodium falciparum

Presentation of the variant antigen, Plasmodium falciparum erythrocyte membrane protein 1 (EMP1), at knob-like protrusions on the surface of infected red blood cells, underpins P. falciparum malaria pathogenicity. Here we describe a protein PF3D7_0301700 (PTP7), that functions at the nexus between the intermediate trafficking organelle, the Maurers cleft, and the infected red blood cell surface. Genetic disruption of PTP7 leads to accumulation of vesicles at the Maurers clefts, grossly aberrant knob morphology, and failure to deliver EMP1 to the red blood cell surface. We show that an expanded low complexity sequence in the C-terminal region of PTP7, found only in the Laverania clade of Plasmodium, is critical for efficient virulence protein trafficking. Author SummaryWe describe a malaria parasite protein involved in virulence factor trafficking (PTP7) that moves between different compartments in the host red blood cell cytoplasm in a stage-dependent manner. Upon disruption of the PTP7 locus, the Maurers cleft trafficking compartments become decorated with vesicles; the knobby protrusions on the host red blood cell surface are depleted and distorted; and trafficking of the virulence protein, EMP1, to the host red blood cell surface is ablated. We provide evidence that a region of PTP7 with low sequence complexity plays an important role in driving fission of vesicles from the Maurers clefts.

biochemistry↗

bioRxiv2020

Pfcerli2, a duplicated gene in the malaria parasite Plasmodium falciparum essential for invasion of erythrocytes as revealed by phylogenetic and cell biological analysis.

Merozoite invasion of host red blood cells (RBCs) is essential for survival of the human malaria parasite Plasmodium falciparum. Proteins involved with RBC binding and invasion are secreted from dual-club shaped organelles at the apical tip of the merozoite called the rhoptries. Here we characterise P. falciparum Cytosolically Exposed Rhoptry Leaflet Interacting protein 2 (PfCERLI2), as a rhoptry bulb protein that is essential for merozoite invasion. Phylogenetic analyses show that cerli2 arose through an ancestral gene duplication of cerli1, a related cytosolically exposed rhoptry bulb protein. We show that PfCERLI2 is essential for blood-stage growth and localises to the cytosolic face of the rhoptry bulb. Inducible knockdown of PfCERLI2 led to an inhibition of merozoite invasion after tight junction formation. PfCERLI2 knockdown was associated with inhibition of rhoptry antigen processing and a significant elongation of the rhoptries, suggesting that the inability of merozoites to invade is caused by aberrant rhoptry function due to PfCERLI2 deficiency. These findings identify PfCERLI2 as a protein that has key roles in rhoptry biology during merozoite invasion.

microbiology↗