Comparative proteomic analysis of soluble and surface-enriched proteins from Acanthamoeba castellanii trophozoites

Acanthamoeba castellanii is a free-living organism widely distributed in the environment that may cause disease. This protozoan exists in two forms, an infective trophozoite and a dormant cyst. The trophozoites are able to cause keratitis and granulomatous amoebic encephalitis in humans. Keratitis is an acute, sight threatening infection of cornea with potential to cause permanent blindness without prompt treatment. However, the lack of suspicion and the low awareness about these amoebae besides of the absence of commercially available immunodiagnostic tests may delay an accurate diagnosis. The identification of proteins with potential for use in immunodiagnosis may improve the parasite detection more quickly and specifically. The amoeba adhesion to the host cell is the primary step for infection but there is no full understanding of A. castellanii proteins relevant for host invasion or infection. In this study, an assessment of soluble and surface-enriched protein fractions expressed by A. castellanii trophozoites, based on complementary LC-MS/MS approach using peptides from SDS-PAGE excised bands, was performed. Our proteomic analysis allowed identification of a total of 503 proteins, of which 308 proteins were exclusively identified in the soluble fraction, 119 in surface-enriched fraction and 76 in both. In silico analysis of functional classification revealed several proteins involved in many biological mechanisms in A. castellanii, including pathogen survival and infection of mammalian hosts. The analysis of predicted antigenic peptides allowed the identification of proteins with potential for immunodiagnostic assays.