Pore-forming polypeptides of the pathogenic protozoon Naegleria fowleri.
The free-living amoeboflagellate and potential human pathogen Naegleria fowleri causes the often fatal disease primary amoebic meningoencephalitis. The molecular repertoire responsible for the cytolytic and tissue-destructive activity of this amoeboid protozoon is largely unknown. We isolated two pore-forming polypeptides from extracts of highly virulent trophozoites of N. fowleri by measuring their membrane-permeabilizing activity. N-terminal sequencing and subsequent molecular cloning yielded the complete primary structures and revealed that the two polypeptides are isoforms. Both polypeptides share similar structural properties with antimicrobial and cytolytic polypeptides of the protozoon Entamoeba histolytica (amoebapores) and of cytotoxic natural killer (NK) and T cells of human (granulysin) and pig (NK-lysin), all characterized by a structure of amphipathic alpha-helices and an invariant framework of cysteine residues involved in disulfide bonds. In contrast to the aforementioned proteins, the Naegleria polypeptides both are processed from large precursor molecules containing additional isoforms of substantial sequence divergence. Moreover, biochemical characterization of the isolated polypeptides in combination with mass determination showed that they are N-glycosylated and variably processed at the C terminus. The biological activity of the purified polypeptides of Naegleria was examined toward human cells and bacteria, and it was found that these factors, named naegleriapores, are active against both types of target cells, which is in good agreement with their proposed biological role as a broad-spectrum effector molecule.
Herbst
Rosa
R
Bernhard Nocht Institute for Tropical Medicine, Bernhard-Nocht-Strasse 74, 20359 Hamburg, Germany.
Ott
Claudia
C
Jacobs
Thomas
T
Marti
Thomas
T
Marciano-Cabral
Francine
F
Leippe
Matthias
M
D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism; D015152:Blotting, Northern; D015139:Blotting, Southern; D001921:Brain / Q000378:metabolism / Q000382:microbiology; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D004748:Entamoeba histolytica / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D006031:Glycosylation; D006801:Humans; D007694:Killer Cells, Natural; D051379:Mice; D008969:Molecular Sequence Data; D016848:Naegleria fowleri / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013601:T-Lymphocytes / Q000378:metabolism; D013997:Time Factors
D000900:Anti-Bacterial Agents; D000945:Antigens, Differentiation, T-Lymphocyte; C075005:GNLY protein, human; D010455:Peptides; D015800:Protozoan Proteins; C459803:naegleriapore A, Naegleria fowleri; C459804:naegleriapore B, Naegleria fowleri