Toxoplasma gondii immune mapped protein 1 is anchored to the inner leaflet of the plasma membrane and adopts a novel protein fold

Co-Immunization with DNA Vaccines Expressing SABP1 and SAG1 Proteins Effectively Enhanced Mice Resistance to Toxoplasma gondii Acute Infection

Toxoplasma gondii (T. gondii) has many intermediate hosts, obligately invades nucleated cells, and seriously threatens human and animal health due to a lack of effective drugs and vaccines. Sialic acid-binding protein 1 (SABP1) is a novel invasion-related protein that, like surface antigen 1 (SAG1), is found on the plasma membrane of T. gondii. To investigate the immunogenicity and protective efficacy of DNA vaccines expressing SABP1 and SAG1 proteins against T. gondii acute infection, the recombinant plasmids pVAX1-SABP1 and pVAX1-SAG1 were produced and administered intramuscularly in Balb/c mice. Serum antibody levels and subtypes, lymphocyte proliferation, and cytokines were used to assess immunized mice's humoral and cellular immune responses. Furthermore, the ability of DNA vaccines to protect mice against T. gondii RH tachyzoites was tested. Immunized mice exhibited substantially higher IgG levels, with IgG2a titers higher than IgG1. When the immune group mice's splenocytes were stimulated with T. gondii lysate antigen, Th1-type cytokines (IL-12p70, IFN-γ, and IL-2) and Th2-type cytokine (IL-4) increased significantly. The combined DNA vaccine significantly increased the immunized mouse survival compared to the control group, with an average death time extended by 4.33 ± 0.6 days (p < 0.0001). These findings show that DNA vaccines based on the SABP1 and SAG1 genes induced robust humoral and cellular immunity in mice, effectively protecting against acute toxoplasmosis and potentially serving as a viable option for vaccination to prevent T. gondii infection.

Profiling of myristoylation in Toxoplasma gondii reveals an N-myristoylated protein important for host cell penetration

N-myristoylation is a ubiquitous class of protein lipidation across eukaryotes and N-myristoyl transferase (NMT) has been proposed as an attractive drug target in several pathogens. Myristoylation often primes for subsequent palmitoylation and stable membrane attachment, however, growing evidence suggests additional regulatory roles for myristoylation on proteins. Here we describe the myristoylated proteome of Toxoplasma gondii using chemoproteomic methods and show that a small-molecule NMT inhibitor developed against related Plasmodium spp. is also functional in Toxoplasma. We identify myristoylation on a transmembrane protein, the microneme protein 7 (MIC7), which enters the secretory pathway in an unconventional fashion with the myristoylated N-terminus facing the lumen of the micronemes. MIC7 and its myristoylation play a crucial role in the initial steps of invasion, likely during the interaction with and penetration of the host cell. Myristoylation of secreted eukaryotic proteins represents a substantial expansion of the functional repertoire of this co-translational modification.

Devitalization of the immune mapped protein 1 undermines the intracellular proliferation of Toxoplasma gondii

The intracellular protozoan Toxoplasma gondii infects approximately one-third of the world's population as well as various animals, causing toxoplasmosis. However, there remains a need to define the functions of newly identified genes of T. gondii. In the present study, a novel molecule, immune mapped protein 1 of T. gondii (TgIMP1), was devitalized by CRISPR/Cas9 system to investigate the phenotypic changes of the parasite. We found that the virulence of ΔTgIMP1 knockout strain was reduced in comparison with wild-type GT1 tachyzoites, showing a statistically decreased plaque in HFF cells and a significantly prolonged survival period of mice (P < 0.05). Moreover, the data of phenotype analyses in vitro showed a different level of the intracellular proliferation and the subsequent egress between ΔTgIMP1 and wild-type GT1 strain (P < 0.05); while no statistically significant difference was detected during the process of attachment or invasion. These results suggested that TgIMP1 is closely associated with the intracellular proliferation of this parasite.

Further confirmation of second- and third-generation Eimeria necatrix merozoite DEGs using suppression subtractive hybridization

In our previous study, we obtained a large number of differentially expressed genes (DEGs) between second-generation merozoites (MZ-2) and third-generation merozoites (MZ-3) of Eimeria necatrix using RNA sequencing (RNA-seq). Here, we report two subtractive cDNA libraries for MZ₂ (forward library) and MZ₃ (reverse library) that were constructed using suppression subtractive hybridization (SSH). PCR amplification revealed that the MZ₂ and MZ₃ libraries contained approximately 96.7% and 95% recombinant clones, respectively, and the length of the inserted fragments ranged from 0.5 to 1.5 kb. A total of 106 and 111 unique sequences were obtained from the MZ₂ and MZ₃ libraries, respectively, and were assembled into 13 specific consensus sequences (contigs or genes) (5 from MZ₂ and 8 from MZ₃). The qRT-PCR results revealed that 11 out of 13 genes were differentially expressed between MZ-2 and MZ-3. Of 13 genes, 11 genes were found in both SSH and our RNA-seq data and displayed a similar expression trend between SSH and RNA-seq data, and the remaining 2 genes have not been reported in both E. necatrix genome and our RNA-seq data. Among the 11 genes, the expression trends of 8 genes were highly consistent between SSH and our RNA-seq data. These DEGs may provide specialized functions related to the life-cycle transitions of Eimeria species.

Humoral and cytokine response elicited during immunisation with recombinant Immune Mapped protein-1 (EtIMP-1) and oocysts of Eimeria tenella

Eimeria tenella, the causative agent of caecal coccidiosis, is a pathogenic gut dwelling protozoan which can cause severe morbidity and mortality in farmed chickens. Immune mapped protein-1 (IMP-1) has been identified as an anticoccidial vaccine candidate; in the present study allelic polymorphism was assessed across the IMP-1 coding sequence in E. tenella isolates from four countries and compared with the UK reference Houghton strain. Nucleotide diversity was low, limited to expansion/contraction of a CAG triplet repeat and five substitutions, three of which were non-synonymous. The EtIMP-1 coding sequence from a cloned Indian E. tenella isolate was expressed in E. coli and purified as a His-tagged thioredoxin fusion protein. An in-vivo vaccination and challenge trial was conducted to test the vaccine potential of recombinant EtIMP-1 (rEtIMP-1) and to compare post-vaccination immune responses of chickens to those stimulated by live oocyst infection. Following challenge, parasite replication measured using quantitative PCR was significantly reduced in chickens that had been vaccinated with rEtIMP-1 (rIC group; 67% reduction compared to UC or unimmunised controls; 79% reduction compared to rTC group or recombinant thioredoxin mock-immunised controls, p<0.05), or the birds vaccinated by infection with oocysts (OC group, 90% compared to unimmunised controls). Chickens vaccinated with oocysts (OC) had significantly higher levels of interferon gamma in their serum post-challenge, compared to rEtIMP-1 vaccinated birds (rIC). Conversely rEtIMP-1 (rIC) vaccinated birds had significantly higher antigen specific serum IgY responses, correlating with higher serum IL-4 (both p<0.05).