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The structure of a major surface antigen SAG19 from Eimeria tenella unifies the Eimeria SAG family.

ABSTRACT: In infections by apicomplexan parasites including Plasmodium, Toxoplasma gondii, and Eimeria, host interactions are mediated by proteins including families of membrane-anchored cysteine-rich surface antigens (SAGs) and SAG-related sequences (SRS). Eimeria tenella causes caecal coccidiosis in chickens and has a SAG family with over 80 members making up 1% of the proteome. We have solved the structure of a representative E. tenella SAG, EtSAG19, revealing that, despite a low level of sequence similarity, the entire Eimeria SAG family is unified by its three-layer αβα fold which is related to that of the CAP superfamily. Furthermore, sequence comparisons show that the Eimeria SAG fold is conserved in surface antigens of the human coccidial parasite Cyclospora cayetanensis but this fold is unrelated to that of the SAGs/SRS proteins expressed in other apicomplexans including Plasmodium species and the cyst-forming coccidia Toxoplasma gondii, Neospora caninum and Besnoitia besnoiti. However, despite having very different structures, Consurf analysis showed that Eimeria SAG and Toxoplasma SRS families each exhibit marked hotspots of sequence hypervariability that map to their surfaces distal to the membrane anchor. This suggests that the primary and convergent purpose of the different structures is to provide a platform onto which sequence variability can be imposed.

SUBMITTER: Ramly NZ

PROVIDER: S-EPMC7979774 | biostudies-literature | 2021 Mar

REPOSITORIES: biostudies-literature

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The structure of a major surface antigen SAG19 from Eimeria tenella unifies the Eimeria SAG family.

Ramly Nur Zazarina NZ Dix Samuel R SR Ruzheinikov Sergey N SN Sedelnikova Svetlana E SE Baker Patrick J PJ Chow Yock-Ping YP Tomley Fiona M FM Blake Damer P DP Wan Kiew-Lian KL Nathan Sheila S Rice David W DW

Communications biology 20210319 1

In infections by apicomplexan parasites including Plasmodium, Toxoplasma gondii, and Eimeria, host interactions are mediated by proteins including families of membrane-anchored cysteine-rich surface antigens (SAGs) and SAG-related sequences (SRS). Eimeria tenella causes caecal coccidiosis in chickens and has a SAG family with over 80 members making up 1% of the proteome. We have solved the structure of a representative E. tenella SAG, EtSAG19, revealing that, despite a low level of sequence simi ...[more]

PMID: 33742128

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Project description:BackgroundChicken coccidiosis, a disease caused by seven species of Eimeria (Apicomplexa: Coccidia), inflicts severe economic losses on the poultry industry. Eimeria tenella is the one of the most virulent species pathogenic to chickens. Many parasitic protozoans are parasitised by double-stranded (ds) RNA viruses, and the influence of protozoan viruses on parasitic protozoans has been extensively reported. E. tenella RNA virus 1 (Etv) was identified in E. tenella, and the complete genome sequence of Etv was analysed. Here, we screened Etv-RNA-dependent RNA polymerase (RDRP)-interacting host protein E. tenella ovarian tumour (OTU) protein-like cysteine protease (Et-OTU) using a yeast two-hybrid system with pGBKT7-RDRP plasmid serving as bait. A previous study demonstrated that Et-OTU could regulate the telomerase activity of E. tenella, indicating that Et-OTU affects E. tenella proliferation. However, whether Etv-RDRP affects the molecular biological characteristics of E. tenella by interacting with OTU remains unclear.ResultsWe obtained seven positive clones from the initial screen, and six of the seven preys were identified as false-positives. Finally, we identified an RDRP-associated protein predicted to be an E. tenella OTU protein. A α-galactosidase assay showed that the bait vector did not activate the GAL4 reporter gene, indicating no autoactivation activity from the RDRP bait fusion. Pull-down and co-immunoprecipitation assays verified the interaction between Et-OTU and Etv-RDRP both intracellularly and extracellularly. Additionally, Et-OTU was able to deconjugate K48- and K6-linked di-ubiquitin (di-Ub) chains in vitro but not K63-, K11-, K29-, or K33-linked di-Ub chains. The C239A and H351A mutations eliminated the deubiquitinase (DUB) activity of Et-OTU, whereas the D236A mutation did not. Additionally, when combined with RDRP, the DUB activity of Et-OTU towards K48- and K6-linked chains was significantly enhanced.ConclusionEtv-RDRP interacts with Et-OTU both intracellularly and extracellularly. Etv-RDRP enhances the hydrolysis of Et-OTU to K6- or K48-linked ubiquitin chains. This study lays the foundation for further research on the relationship between E. tenella and Etv.

Dataset Information

The structure of a major surface antigen SAG19 from Eimeria tenella unifies the Eimeria SAG family.

Publications

The structure of a major surface antigen SAG19 from Eimeria tenella unifies the Eimeria SAG family.

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