Related Experiment Videos
Naegleria fowleri: characterization of a secreted histolytic cysteine protease
K Aldape1, H Huizinga, J Bouvier
1Department of Pathology, University of California, San Francisco 94143.
Abstract:
Naegleria fowleri is the etiologic agent of primary amebic meningoencephalitis, a rare but rapidly fatal disease of humans. It invades the central nervous system via nasal mucosa and cribriform plate. Once in brain tissue, the organism induces an acute hemorrhagic, necrotizing meningoencephalitis. We hypothesize that a protease released by the parasite contributes to tissue destruction and facilitates host invasion. Analysis of conditioned media of N. fowleri cultures revealed a major 30-kDa protease with substrate and inhibitor specificity consistent with cysteine proteases. Amino-terminal amino acid sequence of the purified enzyme showed it to be a thiol protease with homology to cathepsin L. It catalyzed the in vitro degradation of extracellular matrix and had a cytopathic effect on mammalian cells. Both ameba-induced matrix degradation and the cytopathic effect are inhibited by Z-Phe-Ala-fluoromethyl ketone, an irreversible cysteine protease inhibitor. Our results indicate that N. fowleri secretes a cysteine protease with the capacity to destroy host tissue. Naegleria gruberi, a nonpathogenic species, expresses a similar protease but, unlike its pathogenic relative, is not thermotolerant to temperatures above 30 degrees C.
Insights
Naegleria fowleri releases a cysteine protease that destroys host tissue, causing primary amebic meningoencephalitis. This protease facilitates parasite invasion and brain damage, highlighting a key virulence factor.
Area of Science:
- Microbiology
- Parasitology
- Biochemistry
Background:
- Naegleria fowleri causes primary amebic meningoencephalitis (PAM), a rare and fatal human disease.
- PAM involves invasion of the central nervous system through the nasal mucosa, leading to severe brain inflammation and necrosis.
Purpose of the Study:
- To investigate the role of parasite-secreted proteases in Naegleria fowleri pathogenesis.
- To identify and characterize the specific protease involved in tissue destruction and host invasion.
Main Methods:
- Analysis of conditioned media from N. fowleri cultures to identify secreted proteases.
- Purification and biochemical characterization of a 30-kDa cysteine protease.
- In vitro assays to assess the protease's activity on extracellular matrix and mammalian cells.
- Inhibition studies using a specific cysteine protease inhibitor.
Main Results:
- A 30-kDa cysteine protease homologous to cathepsin L was identified in N. fowleri.
- This protease degraded extracellular matrix components in vitro.
- The enzyme exhibited cytopathic effects on mammalian cells.
- Protease activity and cytopathic effects were inhibited by Z-Phe-Ala-fluoromethyl ketone.
Conclusions:
- Naegleria fowleri secretes a potent cysteine protease that contributes to host tissue destruction and PAM pathogenesis.
- This protease is a significant virulence factor for the pathogen.
- A similar protease exists in the nonpathogenic Naegleria gruberi, but it lacks thermotolerance.