Structure and function of a unique pore-forming protein from a pathogenic acanthamoeba

• Published in: Nature chemical biology Vol. 9; no. 1; pp. 37 - 42
• Main Authors: Michalek, Matthias, Sönnichsen, Frank D, Wechselberger, Rainer, Dingley, Andrew J, Hung, Chien-Wen, Kopp, Annika, Wienk, Hans, Simanski, Maren, Herbst, Rosa, Lorenzen, Inken, Marciano-Cabral, Francine, Gelhaus, Christoph, Gutsmann, Thomas, Tholey, Andreas, Grötzinger, Joachim, Leippe, Matthias
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 2013; Nature Publishing Group
• Subjects: 631/326/421; 631/535; 631/92; Acanthamoeba - chemistry; Acanthamoeba - pathogenicity; Acanthamoeba culbertsoni; Amino Acid Sequence; Antimicrobial activity; Bacteria; Biochemical Engineering; Biochemistry; Bioorganic Chemistry; Cell Biology; Chemistry; Chemistry/Food Science; Cytotoxicity; Dimerization; Entamoeba histolytica; Magnetic resonance spectroscopy; Membranes; Models, Molecular; Molecular Sequence Data; Neural stem cells; Parasites; Parasitic protozoa; Pathogens; pH effects; pore-forming proteins; Pores; Protein folding; Protein structure; Protein Structure, Tertiary; Proteins; Protozoan Proteins - chemistry; Protozoan Proteins - physiology; Spectroscopy; Structure-Activity Relationship; Structure-function relationships; Tertiary structure; Toxins; Virulence
• ISSN: 1552-4450; 1552-4469
• DOI: 10.1038/nchembio.1116

Acanthaporin is identified as a pore-forming protein from the infectious Acanthamoeba culbertsoni with a previously unknown structure. The newly identified structure includes a pH-dependent histidine switch that controls partitioning between the inactive dimer and the active monomer, which assembles into larger species to cause toxicity. Human pathogens often produce soluble protein toxins that generate pores inside membranes, resulting in the death of target cells and tissue damage. In pathogenic amoebae, this has been exemplified with amoebapores of the enteric protozoan parasite Entamoeba histolytica. Here we characterize acanthaporin, to our knowledge the first pore-forming toxin to be described from acanthamoebae, which are free-living, bacteria-feeding, unicellular organisms that are opportunistic pathogens of increasing importance and cause severe and often fatal diseases. We isolated acanthaporin from extracts of virulent Acanthamoeba culbertsoni by tracking its pore-forming activity, molecularly cloned the gene of its precursor and recombinantly expressed the mature protein in bacteria. Acanthaporin was cytotoxic for human neuronal cells and exerted antimicrobial activity against a variety of bacterial strains by permeabilizing their membranes. The tertiary structures of acanthaporin's active monomeric form and inactive dimeric form, both solved by NMR spectroscopy, revealed a currently unknown protein fold and a pH-dependent trigger mechanism of activation.