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

The complement regulatory protein (CRP) of Trypanosoma cruzi is a surface glycoprotein which confers to the infectious trypomastigote forms a protection against the lytic activity of the host complement. CRP belongs to the large family of the trans-sialidase-like proteins and its sequence is highly similar to those of the flagellar FL-160 and chronic exoantigen proteins, encoded by a multigene family. To further define the gene family encoding the CRP, we investigated the protein diversity among several strains of T. cruzi through the sequencing of trypomastigote transcripts, and used a phylogenetic analysis based on the multiple alignment of these proteins with the top scoring sequences detected by a database sequence homology search. Intrastrain variations in CRP sequences revealed the existence of several copies per strain. The interstrain variability of CRP was consistent with the genetic subdivisions of T. cruzi into lineages and discrete typing units. The phylogenetic analysis based on a 227 amino acid alignment of CRP sequences with the 200 putative proteins retrieved from the protein databases (including the sequences from the T. cruzi genome project) revealed that the CRP sequences clustered with the FL-160 proteins into a monophyletic group characterized by the presence of the 12 amino acid mimicry epitope that mimics nervous tissues. The phylogeny did not differentiate between the CRP and the FL-160 proteins. The identification of this group of CRP-like proteins and the high sequence similarity observed within it open up new prospects for the exploration of the localization, structure and function of these proteins and a better understanding of their involvement in key aspects of host–parasite interactions, such as the resistance to the complement. This work provides also information for the T. cruzi genome annotation of the trans-sialidase-like putative proteins.
These investigations received financial support from the “Institut de Recherche pour le Développement” (IRD), the “Institut National de la Santé et de la Recherche Médicale” (INSERM), and the French National Programme “ACI Microbiologie” Contract No. MIC 03 29.