ER 50891 br Conflict of interest br Acknowledgements This
Conflict of interest
Acknowledgements This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP: 2014/00926-3).
Introduction The metacestodes of Taenia solium are the causative agent of cysticercosis, which mainly resides the skeletal muscles and the central nervous system in intermediate hosts. The infections with larval T. solium can cause neurocysticercosis with epileptic seizures in humans (Donadeu et al., 2017; White, 2000). Cysticercosis has been defined as the most important foodborne parasitic disease worldwide (Robertson et al., 2013) and a neglected tropical disease (WHO, 2015). This disease is prevalent in rural or marginalized communities of Africa, Asia, Latin America and Europe (Devleesschauwer et al., 2017; Hinojosa-Juarez et al., 2008). In endemic countries, it is known to be a major public health problem and a cause of husbandry economic losses. The helminth proteases were generally described as potential drug targets and vaccine candidates against helminth infections (McKerrow et al., 2006). Importantly, in T. solium, the ER 50891 glycolysis servers as the principal source of energy for the worm growth and other physiological processes, which make glycolytic enzymes be putative therapeutic targets for cysticercosis. Proteomic data also revealed that one of glycolytic enzymes, enolase, was abundant in excretion-secretion (ES) products of various parasites (Bien et al., 2015; Guillou et al., 2007; Victor et al., 2012; Zheng, 2017). Enolase (EC 184.108.40.206) has been known as a key enzyme in glucose metabolism, which is involved in the reversible dehydration of 2-phospho-d-glycerate (2-PGA) to phosphoenolpyruvate (PEP) in the glycolytic and gluconeogenesis pathways (Pal-Bhowmick et al., 2004; Rodriguez et al., 2006). Extensive studies have indicated that enolase exhibits moonlighting functions in various parasites, with the involvement in biological and pathological processes, such as transcriptional regulator (Holmes et al., 2010; Mouveaux et al., 2014), virulence factors (da Fonseca Pires et al., 2014), allergen (Ito et al., 1995), and plasminogen binding receptor (Bernal et al., 2004; Ramajo-Hernandez et al., 2007; Vanegas et al., 2007; Zhang et al., 2015). It is reasonable to assume that T. solium enolase may participate in the certain pathological processes in hosts. However, to our knowledge, limited reports are available concerning its characteristics and functions. In the present study, we described the characterization of a gene that encoded an α-enolase from T. solium (Tseno) and presented its enzymatic activities, tissue localization and the expression patterns at different developmental stages. The results suggest a role of Tseno in invasion and reproduction of T. solium.
Materials and methods
Discussion Enolase is a conserved and crucial multifunctional enzyme, which exists in prokaryote and eukaryote (Pancholi, 2001). In this study, we reported the enzymatic characteristics, plasminogen binding activity, differential expression and immunolocalization of an enolase from T. solium. The phylogenetic analysis showed that Tseno was most closely related to enolases from other Taenia species, such as T. asiatica, T. pisiformis and E. granulosus. Interestingly, Tseno was closer to enolases from cestode-susceptible hosts, including humans and Sus scrofa, than to enolases of parasitic protozoa, such as Plasmodium falciparum, Toxoplasma gondii and Leishmania Mexicana. The conserved sites in the deduced amino acid sequence of Tseno were identical with other helminths, including the enolase signature, substrate-binding sites and Mg2+-binding sites (Bernal et al., 2004; Jolodar et al., 2003; Pancholi, 2001; Ramajo-Hernandez et al., 2007; Vanegas et al., 2007). Like classical properties of other enolase proteins, the purified His-Tseno could efficiently catalyze the conversion of 2-PGA to PEP due to its innate glycolytic activity. The enzyme had optimal activities at pH 7.5, required low concentration of Mg2+ in enzymatic reactions. However, His-Tseno activities were inhibited by NaCl, MgCl2 and CaCl2 with increasing concentrations, but KCl from 50 to 200 mM showed activating effects. The observations were coincided with previous studies on enolases from yeast and Plasmodium (Lee and Nowak, 1992; Pal-Bhowmick et al., 2004). The kinetic analysis showed that the reaction activity of His-Tseno was 60.72 ± 0.84 U/mg and Km for 2-PGA was 1.1 mM. Compared with other organisms, the Km2-PGA value of His-Tseno was higher than ones of T. gondii (Km ≈ 0.078 mM), Clonorchis sinensis (Km ≈ 0.045 mM) and T. pisiformis (Km ≈ 0.77 mM) (Dzierszinski et al., 2001; Wang et al., 2011; Zhang et al., 2015), but lower than ones of Schistosoma japonicum (Km ≈ 1.99 mM) and Streptococcus enolase (Km ≈ 9.5 mM) (Jones and Holt, 2007; Yang et al., 2010). The results showed that His-Tseno had good substrate affinity, which might be adapted to its parasitic environment for energy supplements through anaerobic glycolysis. The researches on enzymatic activity and dynamic characteristic of Tseno will be beneficial to the studies on the mechanisms of substance and energy metabolism in T. solium.