Structural and Functional Characterization of Bc28.1, Major Erythrocyte-binding Protein from Babesia canis Merozoite Surface

Abstract

Babesiosis (formerly known as piroplasmosis) is a tick-borne disease caused by the intraerythrocytic development of protozoa parasites from the genus Babesia. Like Plasmodium falciparum, the agent of malaria, or Toxoplasma gondii, responsible for human toxoplasmosis, Babesia belongs to the Apicomplexa family. Babesia canis is the agent of the canine babesiosis in Europe. Clinical manifestations of this disease range from mild to severe and possibly lead to death by multiple organ failure. The identification and characterization of parasite surface proteins represent major goals, both for the understanding of the Apicomplexa invasion process and for the vaccine potential of such antigens. Indeed, we have already shown that Bd37, the major antigenic adhesion protein from Babesia divergens, the agent of bovine babesiosis, was able to induce complete protection against various parasite strains. The major merozoite surface antigens of Babesia canis have been described as a 28-kDa membrane protein family, anchored at the surface of the merozoite. Here, we demonstrate that Bc28.1, a major member of this multigenic family, is expressed at high levels at the surface of the merozoite. This protein is also found in the parasite in vitro culture supernatants, which are the basis of effective vaccines against canine babesiosis. We defined the erythrocyte binding function of Bc28.1 and determined its high resolution solution structure using NMR spectroscopy. Surprisingly, although these proteins are thought to play a similar role in the adhesion process, the structure of Bc28.1 from B. canis appears unrelated to the previously published structure of Bd37 from B. divergens. Site-directed mutagenesis experiments also suggest that the mechanism of the interaction with the erythrocyte membrane could be different for the two proteins. The resolution of the structure of Bc28 represents a milestone for the characterization of the parasite erythrocyte binding and its interaction with the host immune system.The phylum Apicomplexa, a large group of single-celled eukaryotic intracellular parasites, includes some of the most important pathogenic parasites of humans and animals, the deadliest of which is the malaria parasite Plasmodium falciparum, responsible for one million human deaths per year and with almost half of the human population at risk of contracting malaria. No vaccine currently exists against P. falciparum, and parasites are becoming increasingly resistant to pharmaceuticals. This is also true for other pathogenic Apicomplexa, such as Toxoplasma, which, together with Plasmodium, challenge global human health improvement programs, and coccidiosis and babesiosis are detrimental for agri-business in both industrialized and developing countries. Babesiosis (formerly known as piroplasmosis) is a tick-borne disease caused by the intraerythrocytic development of an Apicomplexa from the Babesia genus. Hemolytic anemia due to parasite development leads to major symptoms, such as hemoglobinury, fever, asthenia, and renal failure. Amo...

Genome-wide analysis of gene expression and protein secretion of Babesia canis during virulent infection identifies potential pathogenicity factors

“…Only Bc28.2, a known secreted B . canis -specific protein 30 with a measured FPKM of 4.5, fell below this threshold. However, the correlation between transcript- and protein abundance is not linear and there is a complex relationship leading to notable discrepancies due to a range of factors such as protein- and mRNA turnover 70 .…”

“…canis ) as well as Bc28 family members (20 gene models) are highly abundant on the merozoite surface but are also shed and interact with the iRBC membrane and the host’s immune system 30 , 31 . Currently, two members of the Bc28 gene family are characterized as major merozoite surface antigens playing a critical function in the interaction of merozoites with RBC 30 , 32 . The second-largest family of exported proteins comprises secreted DnaJ (Hsp40) chaperones (26 members).…”

“…bovis VESA, and 2 merozoite surface antigens of the Bc28 gene family. These proteins where shown to be involved in survival and virulence of several hemoprotozoa species 10 , 18 , 19 , 30 , 62 , 63 . The dataset comprises SA1 and SA3, belonging to the above described third-largest exported family of proteins (secreted antigen family) suggesting a direct role in host-parasite interaction.…”

Evaluation of Babesia gibsoni GPI-anchored Protein 47 (BgGPI47-WH) as a Potential Diagnostic Antigen by Enzyme-Linked Immunosorbent Assay

“…In B. bovis , variable merozoite surface antigens (VMSAs) are important vaccine candidates to control B. bovis , and their antibodies could neutralize the invasion of red blood cells in vitro (20). GPI-anchored proteins have also been identified in Babesia- infected dogs, such as the Bc28 family (10–12). In Toxoplasma gondii , the SAG family has also been identified as an ideal diagnostic antigen and vaccine candidate (21).…”

“…However, there are few reports on GPI-anchored proteins in Babesia- infected dogs. Only the Bc28 multigene family has been reported to play a crucial role in merozoite surface antigens in B. canine (10–12). This implies that GPI-anchored proteins may play a vital role in detection of Babesia .…”