Theoretical investigation on structural, functional and epitope of a 12？kDa excretory-secretory protein from Toxoplasma gondii

An earlier published work discovered a highly antigenic 12？kDa excretory-secretory (ES) protein of T. gondii which may potentially be used for the development of an antigen detection test for toxoplasmosis. However, the three-dimensional structure of the protein is unknown. Since epitope identification is important prior to designing of a specific antibody for an antigen-detection based diagnostic test, the structural elucidation of this protein is essential. In this study, we constructed a three dimensional model of the 12？kDa ES protein. The built structure possesses a thioredoxin backbone which consists of four α-helices flanking five β-strands at the center. Three potential epitopes (6–8 residues) which can be combined into one “single” epitope have been identified from the built structure as the most potential antibody binding site.Together with specific antibody design, this work could contribute towards future development of an antigen detection test for toxoplasmosis.Toxoplasmosis is a disease caused by the intracellular protozoan parasite, Toxoplasma gondii. The disease is estimated to infect more than one-third of the world population [1-5]. Although the infection may show mild symptoms or asymptomatic [6], it can be fatal in an immunocompromised patient or the fetus whose mother acquired primary infection during pregnancy [7]. The life cycle of T. gondii can be divided into two phases, sexual and asexual phase. The sexual phase o the life cycle of T. gondii occurs only in cats (felids; the primary host). The asexual phase occurs in other warm-blooded animals (including humans) where it transmits through food contaminated with the feces of infected cats [8].Due to the high prevalence of toxoplasmosis, especially in third world countries, disease diagnosis and therapy are important. There are a number of diagnostic methods available which include IgM-ELISA, IgG-ELISA, IgG avidity test, Western blots and PCR using body fluids and tissues [9]. Some of these m