Partial purification and characterization of Naegleria fowleri beta-glucosidase

Nf-GH, a glycosidase secreted by Naegleria fowleri, causes mucin degradation: an in vitro and in vivo study

AIM

The aim of this work was to identify, characterize and evaluate the pathogenic role of mucinolytic activity released by Naegleria fowleri.

MATERIALS & METHODS

Zymograms, protease inhibitors, anion exchange chromatography, MALDI-TOF-MS, enzymatic assays, Western blot, and confocal microscopy were used to identify and characterize a secreted mucinase; inhibition assays using antibodies, dot-blots and mouse survival tests were used to evaluate the mucinase as a virulence factor.

RESULTS

A 94-kDa protein with mucinolytic activity was inducible and abolished by p-hydroxymercuribenzoate. MALDI-TOF-MS identified a glycoside hydrolase. Specific antibodies against N. fowleri-glycoside hydrolase inhibit cellular damage and MUC5AC degradation, and delay mouse mortality.

CONCLUSION

Our findings suggest that secretory products from N. fowleri play an important role in mucus degradation during the invasion process.

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Iron-Binding Protein Degradation by Cysteine Proteases of Naegleria fowleri

Naegleria fowleri causes acute and fulminant primary amoebic meningoencephalitis. This microorganism invades its host by penetrating the olfactory mucosa and then traveling up the mesaxonal spaces and crossing the cribriform plate; finally, the trophozoites invade the olfactory bulbs. During its invasion, the protozoan obtains nutrients such as proteins, lipids, carbohydrates, and cationic ions (e.g., iron, calcium, and sodium) from the host. However, the mechanism by which these ions are obtained, particularly iron, is poorly understood. In the present study, we evaluated the ability of N. fowleri to degrade iron-binding proteins, including hololactoferrin, transferrin, ferritin, and hemoglobin. Zymography assays were performed for each substrate under physiological conditions (pH 7 at 37°C) employing conditioned medium (CM) and total crude extracts (TCEs) of N. fowleri. Different degradation patterns with CM were observed for hololactoferrin, transferrin, and hemoglobin; however, CM did not cause ferritin degradation. In contrast, the TCEs degraded only hololactoferrin and transferrin. Inhibition assays revealed that cysteine proteases were involved in this process. Based on these results, we suggest that CM and TCEs of N. fowleri degrade iron-binding proteins by employing cysteine proteases, which enables the parasite to obtain iron to survive while invading the central nervous system.

Comparative study of free and membrane-bound acidic beta-D-glucosidase from the hepatopancreas of the shrimp Penaeus japonicus (Crustacea: decapoda)

l. In the hepatopancreas of the shrimp Penaeus japonicus the beta-glucosidase is present, either free or membrane-bound. The specific activity of the purified enzyme is 237,333 units/mg of protein and 191,111 units/mg of protein for the free and the membrane-bound beta-glucosidase, respectively. 2.The non-membrane-bound beta-glucosidase appears to be the same molecular size as the membrane-bound enzyme, both being monomers and consisting of a polypeptide chain of apparent M(r) 65,000, as estimated by chromatography on Superose 12 and by SDS-PAGE. 3.Both enzymes share similarities in their molecular size and substrate specificities (with ratios of 100:17:4:12 for the non-membrane-bound and 100:32:13:12 for the membrane-bound enzyme for the activities with methylumbelliferyl-beta-D-glucoside, methylumbelliferyl-beta-D-galactoside, methylumbelliferyl-alpha -L-arabinopyranoside and methylumbelliferyl-beta-xyloside respectively, as substrates). 4.The membrane-bound beta-glucosidase can be differentiated from the non-membrane-bound enzyme by its isoelectric point (7.5 vs 6.6), Km (182 micrometer vs 76 micrometer), pH optimum (4.5 vs 5.5), phosphorylation,sialyation and thermostability.

[A comparative study on hydrolase activities in Acanthamoeba culbertsoni and A. royreba]

Specific or non-specific cytolytic processes of free-living amoebae causing meningoencephalitis have been emphasized and the cytolytic ability related to hydrolases in Entamoeba sp. and Naegleria sp. has also been reported since the latter half of 1970's. However, no information on hydrolase activities in Acanthamoeba sp. is available. Hydrolases in Acanthamoeba culbertsoni, a pathogenic species of free-living amoebae, were assayed and compared with those in a non-pathogenic species, A. royreba. Pathogenicity of these two species was confirmed through experimental infection to BALB/c mice. Hydrolase activities and cytotoxic effects between pathogenic and non-pathogenic species were compared in the trophozoites cultured in CGV media and in CHO cell line, respectively. The results are summarized as follows: The mice infected with A. culbertsoni were all dead 15 days after nasal inoculation, and the mean survival time was 8.5 days. Also the mice infected with this pathogenic species mani fested typical meningoencephalitis, whereas the mice infected with A. royreba did not. Hydrolases detected both in the cell extracts and culture media were acid phosphatase, beta-N-acetyl galactosaminidase, beta-N-acetyl glucosaminidase, alpha-mannosidase, neutral proteinase and acid proteinase, all of which were detected with remarkably higher rate in A.culbertsoni than in A. royreba. A. culbertsoni revealed strong cytotoxicity for the target CHO cells, whereas A. royreba did not show any specific cytotoxicity. About 80% of the target cells mixed with A. culbertsoni were dead 48 hours after cultivation, and more than 95% of the target cells were dead 72 hours after cultivation. Hydrolase activities in A. culbertsoni cultured with the target cell line were assayed according to the culture time. The activities of acid phosphatase, beta-N-acetyl glucosaminidase, beta-N-acetyl glucosaminidase, alpha-mannosidase and acid proteinase in this pathogenic amoeba were detected higher in amoeba extracts than in culture media up to 120 hours after cultivation, but after 120 hours of cultivation those activities were detected higher in culture media than in the amoeba lysates. Neutral proteinase activity in A. culbertsoni increased more in EBSS medium than in the lysate specimens although the activity in the extracts was generally steady according to the cultivation time. Summarizing the above results, it is concluded that there were differences in hydrolase activities between pathogenic A. culbertsoni and non-pathogenic A. royreba, and that some hydrolase activities were detected remarkably higher in A. culbertsoni which revealed strong cytotoxicity to the target CHO cell line.

Biology of Naegleria spp

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