Membrane Activity and Channel Formation of the Adenylate Cyclase Toxin (CyaA) of Bordetella pertussis in Lipid Bilayer Membranes.

Oliver Knapp,Roland Benz

doi:10.3390/toxins12030169

Abstract

The Gram-negative bacterium Bordetella pertussis is the cause of whooping cough. One of its pathogenicity factors is the adenylate cyclase toxin (CyaA) secreted by a Type I export system. The 1706 amino acid long CyaA (177 kDa) belongs to the continuously increasing family of repeat in toxin (RTX) toxins because it contains in its C-terminal half a high number of nine-residue tandem repeats. The protein exhibits cytotoxic and hemolytic activities that target primarily myeloid phagocytic cells expressing the αMβ2 integrin receptor (CD11b/CD18). CyaA represents an exception among RTX cytolysins because the first 400 amino acids from its N-terminal end possess a calmodulin-activated adenylate cyclase (AC) activity. The entry of the AC into target cells is not dependent on the receptor-mediated endocytosis pathway and penetrates directly across the cytoplasmic membrane of a variety of epithelial and immune effector cells. The hemolytic activity of CyaA is rather low, which may have to do with its rather low induced permeability change of target cells and its low conductance in lipid bilayer membranes. CyaA forms highly cation-selective channels in lipid bilayers that show a strong dependence on aqueous pH. The pore-forming activity of CyaA but not its single channel conductance is highly dependent on Ca2+ concentration with a half saturation constant of about 2 to 4 mM.

Highlights

Whooping cough is a highly transmissive disease of the human respiratory tract caused by theGram-negative bacterium Bordetella pertussis
Key Contribution: This review focuses on the ability of the adenylate cyclase toxin (CyaA) of Bordetella pertussis to form cation selective transient ion-permeable channels on artificial and target cell membranes
A special focus has to be set on pore formation, since it is possible that the pore-forming activities of repeat in toxin (RTX) toxins allow the permeation of small molecules through the target cell membrane, including calcium ions, which start the inflammatory reactions and possibly cell lysis [99,100,101]

Summary

Introduction

Whooping cough is a highly transmissive disease of the human respiratory tract caused by the. The domain between residues 913 and 1612 contains about 45 glycine and aspartate-rich nonapeptide tandem repeats of the form of the type G-G-X-G-(N/D)-D-X-(L/I/F)-X (where X represents any amino acid) that form calcium-binding sites These repeats are typical for RTX toxins (see Figure 1). The last about 50 to 60 amino acids from the C-terminal end of CyaA (see Figure 1) represent the export signal because it is actively secreted from B. pertussis by a specific type I transport system [43,44] It consists of the products of the genes cyaB and cyaD, which are homologues of the proteins involved in E. coli hemolysin export machinery [43,44,45]. This raises the possibility that the initial unsaturable binding of RTX cytotoxins to various cells might occur through the recognition of glycosylated membrane components such as glycoproteins and gangliosides

Membrane Interaction of CyaA

Factors Affecting CyaA Channel-Forming Activity

Conclusions