High immunological response against a Trypanosoma equiperdum protein that exhibits homology with the regulatory subunits of mammalian cAMP-dependent protein kinases

Reversible phosphorylation of a protein from Trypanosoma equiperdum that exhibits homology with the regulatory subunits of mammalian cAMP-dependent protein kinases

Homologous proteins of the cAMP-dependent protein kinase (PKA) regulatory and catalytic subunits have been identified in Trypanosoma equiperdum (TeqR-like and TeqC-like, respectively). Partially purified TeqR-like from parasites isolated in the presence of glucose migrated as an apparent 55 kDa/57 kDa polypeptide doublet when separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, a single polypeptide of 57 kDa was obtained when parasites were deprived of glucose, a condition that has been shown to activate a TeqC-like enzyme. As revealed by immunoblots using anti-phospothreonine antibodies, the 57 kDa band corresponded to a form of TeqR-like that was phosphorylated in threonine residues. TeqR-like phosphorylation was reversible since the level of phospho-TeqR-like decreased once glucose was readded to glucose starved-parasites. Dephospho- and phospho-TeqR-like proteins are monomers with native molecular masses of 54.93-57.41 kDa, Stokes radii of 3.42-3.37 nm, and slightly asymmetric shapes (frictional ratio f/fo = 1.36-1.32). A protein kinase of ∼40 kDa was also partially purified from glucose deprived-trypanosomes, which corresponded to the TeqC-like enzyme by its ability to phosphorylate kemptide, its inhibition by PKA-specific inhibitors, and its immunorecognition by anti-PKA catalytic subunit antibodies. TeqR-like and TeqC-like did not coelute following anion-exchange chromatography, revealing that these proteins are not associated forming a complex in T. equiperdum. Yet, when TeqR-like was incubated in vitro with TeqC-like in the presence of Mg²⁺ and ATP, the 55 kDa dephospho form of the 55kDa/57 kDa polypeptide doublet of TeqR-like was converted into the 57 kDa phospho form, demonstrating that TeqR-like is a substrate for TeqC-like.

Equine trypanosomosis: enigmas and diagnostic challenges

Equine trypanosomosis is a complex of infectious diseases called dourine, nagana and surra. It is caused by several species of the genus Trypanosoma that are transmitted cyclically by tsetse flies, mechanically by other haematophagous flies, or sexually. Trypanosoma congolense (subgenus Nannomonas) and T. vivax (subgenus Dutonella) are genetically and morphologically distinct from T. brucei, T. equiperdum and T. evansi (subgenus Trypanozoon). It remains controversial whether the three latter taxa should be considered distinct species. Recent outbreaks of surra and dourine in Europe illustrate the risk and consequences of importation of equine trypanosomosis with infected animals into non-endemic countries. Knowledge on the epidemiological situation is fragmentary since many endemic countries do not report the diseases to the World Organisation for Animal Health, OIE. Other major obstacles to the control of equine trypanosomosis are the lack of vaccines, the inability of drugs to cure the neurological stage of the disease, the inconsistent case definition and the limitations of current diagnostics. Especially in view of the ever-increasing movement of horses around the globe, there is not only the obvious need for reliable curative and prophylactic drugs but also for accurate diagnostic tests and algorithms. Unfortunately, clinical signs are not pathognomonic, parasitological tests are not sufficiently sensitive, serological tests miss sensitivity or specificity, and molecular tests cannot distinguish the taxa within the Trypanozoon subgenus. To address the limitations of the current diagnostics for equine trypanosomosis, we recommend studies into improved molecular and serological tests with the highest possible sensitivity and specificity. We realise that this is an ambitious goal, but it is dictated by needs at the point of care. However, depending on available treatment options, it may not always be necessary to identify which trypanosome taxon is responsible for a given infection.