Invasion of human erythrocytes by Plasmodium falciparum merozoites involves multiple interactions between host receptors and their merozoite ligands. Here we report human Cyclophilin B as a receptor for PfRhopH3 during merozoite invasion. Localization and binding studies show that Cyclophilin B is present on the erythrocytes and binds strongly to merozoites. We demonstrate that PfRhopH3 binds to the RBCs and their treatment with Cyclosporin A prevents merozoite invasion. We also show a multi-protein complex involving Cyclophilin B and Basigin, as well as PfRhopH3 and PfRh5 that aids the invasion. Furthermore, we report identification of a de novo peptide CDP3 that binds Cyclophilin B and blocks invasion by up to 80%. Collectively, our data provide evidence of compounded interactions between host receptors and merozoite surface proteins and paves the way for developing peptide and small-molecules that inhibit the protein−protein interactions, individually or in toto, leading to abrogation of the invasion process.

Apicomplexan parasites, through their motor machinery, produce the required propulsive force critical for host cell-entry. The conserved components of this so-called glideosome machinery are myosin A and myosin A Tail Interacting Protein (MTIP). MTIP tethers myosin A to the inner membrane complex of the parasite through 20 amino acid-long C-terminal end of myosin A that makes direct contacts with MTIP, allowing the invasion of Plasmodium falciparum in erythrocytes. Here, we discovered through screening a peptide library, a de-novo peptide ZA1 that binds the myosin A tail domain. We demonstrated that ZA1 bound strongly to myosin A tail and was able to disrupt the native myosin A tail MTIP complex both in vitro and in vivo. We then showed that a shortened peptide derived from ZA1, named ZA1S, was able to bind myosin A and block parasite invasion. Overall, our study identified a novel anti-malarial peptide that could be used in combination with other antimalarials for blocking the invasion of Plasmodium falciparum.

Hijacking of host metabolic status by a pathogen for its regulated dissemination from the host is prerequisite for the propagation of infection. M. tuberculosis secretes an NAD+-glycohydrolase, TNT, to induce host necroptosis by hydrolyzing Nicotinamide adenine dinucleotide (NAD+). Herein, we expressed TNT in macrophages and erythrocytes; the host cells for M. tuberculosis and the malaria parasite respectively, and found that it reduced the NAD+ levels and thereby induced necroptosis and eryptosis resulting in premature dissemination of pathogen. Targeting TNT in M. tuberculosis or induced eryptosis in malaria parasite interferes with pathogen dissemination and reduction in the propagation of infection. Building upon our discovery that inhibition of pathogen-mediated host NAD+ modulation is a way forward for regulation of infection, we synthesized and screened some novel compounds that showed inhibition of NAD+-glycohydrolase activity and pathogen infection in the nanomolar range. Overall this study highlights the fundamental importance of pathogen-mediated modulation of host NAD+ homeostasis for its infection propagation and novel inhibitors as leads for host-targeted therapeutics.

SUMOylation is one of the post-translational modifications that have recently been described as a key regulator of various cellular, nuclear, metabolic, and immunological processes. The process of SUMOylation involves the modification of one or more lysine residues of target proteins by conjugation of a ubiquitin-like, small polypeptide known as SUMO for their degradation, stability, transcriptional regulation, cellular localization, and transport. Herein, for the first time, we report the involvement of the host SUMOylation pathway in the process of infection of Leishmania donovani, a causative agent of visceral leishmaniasis. Our data revealed that infection of L. donovani to the host macrophages leads to upregulation of SUMOylation pathway genes and downregulation of a deSUMOylating gene, SENP1. Further, to confirm the effect of the host SUMOylation on the growth of Leishmania, the genes associated with the SUMOylation pathway were silenced and parasite load was analyzed. The knockdown of the SUMOylation pathway led to a reduction in parasitic load, suggesting the role of the host SUMOylation pathway in the disease progression and parasite survival. Owing to the effect of the SUMOylation pathway in autophagy, we further investigated the status of host autophagy to gain mechanistic insights into how SUMOylation mediates the regulation of growth of L. donovani. Knockdown of genes of host SUMOylation pathway led to the reduction of the expression levels of host autophagy markers while promoting autophagosome–lysosome fusion, suggesting SUMOylation-mediated autophagy in terms of autophagy initiation and autophagy maturation during parasite survival. The levels of reactive oxygen species (ROS) generation, nitric oxide (NO) production, and pro-inflammatory cytokines were also elevated upon the knockdown of genes of the host SUMOylation pathway during L. donovani infection. This indicates the involvement of the SUMOylation pathway in the modulation of protective immune responses and thus favoring parasite survival. Taken together, the results of this study indicate the hijacking of the host SUMOylation pathway by L. donovani toward the suppression of host immune responses and facilitation of host autophagy to potentially facilitate its survival. Targeting of SUMOylation pathway can provide a starting point for the design and development of novel therapeutic interventions to combat leishmaniasis.

The emergence of Plasmodium falciparum resistance raises an urgent need to find new antimalarial drugs. Here, we report the rational repurposing of the anti-hepatitis C virus drug, alisporivir, a nonimmunosuppressive analog of cyclosporin A, against artemisinin-resistant strains of P. falciparum . In silico docking studies and molecular dynamic simulation predicted strong interaction of alisporivir with Pf Cyclophilin 19B, confirmed through biophysical assays with a K d value of 354.3 nM.