Oxidative reactions can modulate Giardia lamblia ecto-phosphatase activity.
Cosentino-Gomes, D., Amazonas, J. N. and Meyer-Fernandes, J. R.
Laboratório de Bioquímica Celular, IBqM, CCS, UFRJ, RJ.
E-mail: cosentino@bioqmed.ufrj.br
Giardia lamblia, a parasite flagellated protozoon, is the causative agent of giardiasis, the most common diarrheal illness worldwide. This parasitic organism has a simple life cycle, alternating between the disease-causing trophozoite and the environmentally resistant cyst, which is responsible for the transmission of disease among susceptible hosts.
For these protozoa, it is very important to perceive stimulus from environment. In this broad context, membrane proteins which have their catalytic site faced to extracellular medium, as ecto-phosphatases proteins, constitute a primordial signaling pathway. Several functions are described for ecto-phosphatases such as the process of parasite adhesion to host cell, cell division, nutrient acquisition and regulation of encystation process of this parasite.
In this study, we investigated the regulation of ecto-phosphatase activity in G. lamblia by oxidative stress generated in reactions using different metals, Fe2+, Fe3+, Cu1+ and Cu2+. Fe2+ is not able to modulate ecto-phosphatase as well as Fe3+ and Cu2+ alone. On the other hand, Cu1+ stimulates this activity during pre-incubation time of 60 minutes. This response is higher in the first 10 minutes, decreasing according to time until the end of pre-incubation time. When Fe2+ reacts with ascorbate and hydrogen peroxide (Fenton-like process), ecto-phosphatase activity is stimulated in 60% in a time dependent manner. Using the same reagents of Fenton's reaction, but changing the metal, Fe3+ stimulates 200% in a initial time and then is reverted in a time dependent manner. This behaviour is also observed with Cu2+, while Cu1+ enhances this activity around 60% during 20 minutes and after this time begins to decrease. Previous data suggest that this reaction can be modulated by reductive agents like DTT.
Our research group has demonstrated that ecto-phosphatase from G. lamblia participates in the process of parasite encystation, since this activity is increased during the transformation of trophozoites into cysts. So, these results reveal a new form to modulate ecto-phosphatase activity and an important target to regulate the encystation process of G. lamblia.
This work was supported by CNPq and FAPERJ.
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