A comparative study of the membrane proteins from Naegleria species: A 23-kDa protein participates in the virulence of Naegleria fowleri

The plasma membrane is essential in the pathogenicity of several microorganisms. However, to date, there are few studies related to the plasma membrane proteins in Naegleria fowleri; this amoeba produces a fatal disease called primary amoebic meningoencephalitis. In the present study, we analyzed the electrophoretic pattern of the membrane proteins of N. fowleri and compared it with the nonpathogenic N. lovaniensis and N. gruberi. We detected a 23-kDa protein (Nf23) present at a higher level in N. fowleri than in the nonpathogenic amoebae. The mass spectrometry analysis showed that the Nf23 protein has a sequence of 229 amino acids that corresponds to a membrane protein. The mRNA level of nf23 was overexpressed 4-fold and 40,000-fold in N. fowleri compared with N. lovaniensis and N. gruberi, respectively. Moreover, we found a 5-fold overexpression of nf23 in N. fowleri trophozoites recovered from mouse brains compared with trophozoites axenically cultivated. In addition, the cytopathic effect on Madin-Darby Canine Kidney cells coincubated with N. fowleri diminished in the presence of antibodies against Nf23; nevertheless, the nonpathogenic amoebae did not produce damage to the monolayer cells. These results suggest that the plasma membrane protein Nf23 is probably involved in the virulence of N. fowleri.