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Evidence of the presence of a calmodulin-sensitive plasma membrane Ca<sup>2+</sup>-ATPase in Trypanosoma equiperdum

Abstract:

Trypanosoma equiperdum belongs to the subgenus Trypanozoon, which has a significant socio-economic impact by limiting animal protein productivity worldwide. Proteins involved in the intracellular Ca2+ regulation are prospective chemotherapeutic targets since several drugs used in experimental treatment against trypanosomatids exert their action through the disruption of the parasite intracellular Ca2+ homeostasis. Therefore, the plasma membrane Ca2+-ATPase (PMCA) is considered as a potential drug target. This is the first study revealing the presence of a PMCA in T. equiperdum (TePMCA) showing that it is calmodulin (CaM) sensitive, revealed by ATPase activity, western-blot analysis and immuno-absorption assays. The cloning sequence for TePMCA encodes a 1080 amino acid protein which contains domains conserved in all PMCAs so far studied. Molecular modeling pbkp_redicted that the protein has 10 transmembrane and three cytoplasmic loops which include the ATP-binding site, the phosphorylation domain and Ca2+ translocation site. Like all PMCAs reported in other trypanosomatids, TePMCA lacks a classic CaM binding domain. Nevertheless, this enzyme presents in the C-terminal tail a region of 28 amino acids (TeC28), which most likely adopts a helical conformation within a 1–18 CaM binding motif. Molecular docking between Trypanosoma cruzi CaM (TcCaM) and TeC28 shows a significant similarity with the CaM-C28PMCA4b reference structure (2kne). TcCaM-TeC28 shows an anti-parallel interaction, the peptide wrapped by CaM and the anchor buried in the hydrophobic pocket, structural characteristic described for similar complexes. Our results allows to conclude that T. equiperdum possess a CaM-sensitive PMCA, which presents a non-canonical CaM binding domain that host a 1–18 motif.