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Clostridium botulinum C2 toxin: binding studies with fluorescence-activated cytometry.
Bradley G Stiles1, Dagmar Blöcker, Martha L Hale
1Department of Immunology and Molecular Biology, US Army Medical Research Institute of Infectious Diseases, Frederick MD 21702-5011, USA. bradley.stiles@amedd.army.mil
Summary
Clostridium botulinum C2 enterotoxin uses fluorescence-activated cytometry to show how its components, C2I and C2IIa, bind to cells. This method effectively studies bacterial binary toxin interactions and receptor binding.
Area of Science:
- Microbiology
- Cell Biology
- Biochemistry
Background:
- Clostridium botulinum C2 enterotoxin is a binary toxin composed of C2I (ADP-ribosyltransferase) and C2II (cell-binding protein).
- C2II recognizes a cell-surface glycoprotein, facilitating C2I translocation into the target cell cytosol.
- Understanding the binding characteristics of such toxins is crucial for elucidating their pathogenic mechanisms.
Purpose of the Study:
- To investigate the cellular interactions and binding properties of Clostridium botulinum C2 enterotoxin components using fluorescence-activated cytometry.
- To characterize the role of C2II in cell binding and C2I translocation.
- To evaluate the utility of fluorescence-activated cytometry in studying bacterial binary toxins.
Main Methods:
- Alexa488-labeled C2I (C2I-A488) and proteolytically activated C2II (C2IIa-A488) were used to study cellular interactions.
- Fluorescence-activated cytometry was employed to quantify toxin binding to Chinese hamster ovary (CHO) and African green monkey kidney (Vero) cells.
- Competition assays with unlabeled C2I and enzymatic treatments (pronase, papain) were performed to assess specificity and receptor involvement.
Main Results:
- C2IIa-A488 binding to CHO and Vero cells showed significant signal/noise ratios (7:1 and 4:1, respectively).
- C2I-A488 binding was dependent on C2IIa and exhibited high signal/noise ratios (4:1 on CHO, 10:1 on Vero), with effective competition by unlabeled C2I.
- Toxin binding was abolished in a CHO cell line lacking the C2IIa receptor and was not observed with the related iota toxin component.
- Enzymatic pretreatment with pronase or papain at 37°C abolished C2IIa binding, while papain treatment at 25°C enhanced it.
Conclusions:
- Fluorescence-activated cytometry is a valuable tool for studying the binding characteristics of bacterial binary toxins like C2.
- The study confirms the specific cell-surface receptor interaction mediated by C2IIa for C2 enterotoxin.
- The findings provide insights into the molecular mechanisms of C2 enterotoxin cell entry and highlight the utility of flow cytometry in toxin research.