Exploring the FL-160-CRP gene family through sequence variability of the complement regulatory protein (CRP) expressed by the trypomastigote stage of Trypanosoma cruzi

Is It Possible to Intervene in the Capacity of Trypanosoma cruzi to Elicit and Evade the Complement System?

Chagas' disease is a zoonotic parasitic ailment now affecting more than 6 million people, mainly in Latin America. Its agent, the protozoan Trypanosoma cruzi, is primarily transmitted by endemic hematophagous triatomine insects. Transplacental transmission is also important and a main source for the emerging global expansion of this disease. In the host, the parasite undergoes intra (amastigotes) and extracellular infective (trypomastigotes) stages, both eliciting complex immune responses that, in about 70% of the cases, culminate in permanent immunity, concomitant with the asymptomatic presence of the parasite. The remaining 30% of those infected individuals will develop a syndrome, with variable pathological effects on the circulatory, nervous, and digestive systems. Herein, we review an important number of T. cruzi molecules, mainly located on its surface, that have been characterized as immunogenic and protective in various experimental setups. We also discuss a variety of parasite strategies to evade the complement system - mediated immune responses. Within this context, we also discuss the capacity of the T. cruzi infective trypomastigote to translocate the ER-resident chaperone calreticulin to its surface as a key evasive strategy. Herein, it is described that T. cruzi calreticulin inhibits the initial stages of activation of the host complement system, with obvious benefits for the parasite. Finally, we speculate on the possibility to experimentally intervene in the interaction of calreticulin and other T. cruzi molecules that interact with the complement system; thus resulting in significant inhibition of T. cruzi infectivity.

Genomic assemblies of newly sequenced Trypanosoma cruzi strains reveal new genomic expansion and greater complexity

Chagas disease is a complex illness caused by the protozoan Trypanosoma cruzi displaying highly diverse clinical outcomes. In this sense, the genome sequence elucidation and comparison between strains may lead to disease understanding. Here, two new T. cruzi strains, have been sequenced, Y using Illumina and Bug2148 using PacBio, assembled, analyzed and compared with the T. cruzi annotated genomes available to date. The assembly stats from the new sequences show effective improvement of T. cruzi genome over the actual ones. Such as, the largest contig assembled (1.3 Mb in Bug2148) in de novo attempts and the highest mean assembly coverage (71X for Y). Our analysis reveals a new genomic expansion and greater complexity for those multi-copy gene families related to infection process and disease development, such as Trans-sialidases, Mucins and Mucin Associated Surface Proteins, among others. On one side, we demonstrate that multi-copy gene families are located near telomeric regions of the "chromosome-like" 1.3 Mb contig assembled of Bug2148, where they likely suffer high evolutive pressure. On the other hand, we identified several strain-specific single copy genes that might help to understand the differences in infectivity and physiology among strains. In summary, our results indicate that T. cruzi has a complex genomic architecture that may have promoted its evolution.

Trypanosoma cruzi Trans-sialidase: structural features and biological implications

Trypanosoma cruzi trans-sialidase (TcTS) has intrigued researchers all over the world since it was shown that T. cruzi incorporates sialic acid through a mechanism independent of sialyltransferases. The enzyme has being involved in a vast myriad of functions in the biology of the parasite and in the pathology of Chagas' disease. At the structural level experiments trapping the intermediate with fluorosugars followed by peptide mapping, X-ray crystallography, molecular modeling and magnetic nuclear resonance have opened up a three-dimensional understanding of the way this enzyme works. Herein we review the multiple biological roles of TcTS and the structural studies that are slowly revealing the secrets underlining an efficient sugar transfer activity rather than simple hydrolysis by TcTS.

Trypanosoma carassii calreticulin binds host complement component C1q and inhibits classical complement pathway-mediated lysis

Trypanosoma carassii is an extracellular parasite of economically important fish species that has evolved several strategies to circumvent host immune responses. Proteomic analysis of the excreted/secreted (ES) and surface molecules of the parasite has revealed a number of proteins that may be involved in host-parasite interactions. Among the parasite molecules identified in the ES of T. carassii was calreticulin. We cloned and produced T. carassii calreticulin (rTcaCRT), and generated a rabbit polyclonal antibody to the recombinant protein. The incubation of parasites with rabbit anti-rTcaCRT affinity-purified IgG antibody indicated substantial CRT levels on the surface of trypanosomes, as well as internal structures of permeabilized organisms. Recombinant parasite calreticulin bound several molecules in host serum including the first complement component, C1q. The host C1q specifically interacted with parasite CRT since the C1q-dependent lysis of sensitized sheep erythrocytes was inhibited by rTcaCRT. Our findings suggest that CRT may be used by the parasite to inhibit hosts' classical complement pathway.