Pilpa RM, Bayrhuber M, Marlett JM, Riek R, Young JAT. A receptor-based switch that regulates anthrax toxin pore formation.
PLoS Pathog 2011;
7:e1002354. [PMID:
22174672 PMCID:
PMC3234216 DOI:
10.1371/journal.ppat.1002354]
[Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Accepted: 09/19/2011] [Indexed: 11/19/2022] Open
Abstract
Cellular receptors can act as molecular switches, regulating the sensitivity of microbial proteins to conformational changes that promote cellular entry. The activities of these receptor-based switches are only partially understood. In this paper, we sought to understand the mechanism that underlies the activity of the ANTXR2 anthrax toxin receptor-based switch that binds to domains 2 and 4 of the protective antigen (PA) toxin subunit. Receptor-binding restricts structural changes within the heptameric PA prepore that are required for pore conversion to an acidic endosomal compartment. The transfer cross-saturation (TCS) NMR approach was used to monitor changes in the heptameric PA-receptor contacts at different steps during prepore-to-pore conversion. These studies demonstrated that receptor contact with PA domain 2 is weakened prior to pore conversion, defining a novel intermediate in this pathway. Importantly, ANTXR2 remained bound to PA domain 4 following pore conversion, suggesting that the bound receptor might influence the structure and/or function of the newly formed pore. These studies provide new insights into the function of a receptor-based molecular switch that controls anthrax toxin entry into cells.
The bacterium that causes anthrax produces a toxin called anthrax toxin that is largely responsible for causing disease symptoms. The first step in anthrax intoxication involves binding of the toxin to a specific protein, called a receptor, on the cell surface. Receptor-binding acts like a switch to prevent the toxin from forming a pore in a cell membrane until the toxin-receptor complex is taken up into cells and delivered to a specific location (called an endosome) where it is exposed to an “acid bath”. This acidic environment promotes structural changes in the toxin leading to pore formation in the endosomal membrane. In this report, we have studied how the receptor regulates pore formation by following the associated changes in toxin-receptor contacts. These studies have defined a new toxin-receptor intermediate in the pathway leading to pore conversion and demonstrate that the receptor remains bound after pore conversion. Our results provide important new insights into how the receptor regulates anthrax toxin pore formation, information that could be useful for designing new therapeutic strategies to treat this disease.
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