Diphtheria Toxin Forms Pores of Different Sizes Depending on Its Concentration in Membranes: Probable Relationship to Oligomerization (original) (raw)

Abstract.

Diphtheria toxin forms pores in biological and model membranes upon exposure to low pH. These pores may play a critical role in the translocation of the A chain of the toxin into the cytoplasm. The effect of protein concentration on diphtheria toxin pore formation in model membrane systems was assayed by using a new fluorescence quenching method. In this method, the movement of Cascade Blue labeled dextrans of various sizes across membranes is detected by antibodies which quench Cascade Blue fluorescence. It was found that at low pH the toxin makes pores in phosphatidylcholine/phosphatidylglycerol vesicles with a size that depends on protein concentration. At the lowest toxin concentrations only the entrapped free fluorophore (MW 538) could be released from model membranes. At intermediate toxin concentrations, a 3 kD dextran could be released. At the highest toxin concentration, a 10 kD dextran could be released, but not a 70 kD dextran. Similar pore properties were found using vesicles lacking phosphatidylglycerol or containing 30% cholesterol. However, larger pores formed at lower protein concentrations in the presence of cholesterol. The dependence of pore size on toxin concentration suggests that toxin oligomerization regulates pore size. This behavior may explain some of the conflicting data on the size of the pores formed by diphtheria toxin. The formation of oligomers by membrane-inserted toxin is consistent with the results of chemical crosslinking and measurements of the self-quenching of rhodamine-labeled toxin. Based on these experiments we propose diphtheria toxin forms oligomers with a variable stoichiometry, and that pore size depends on the oligomerization state. Reasons why oligomerization could assist proper membrane insertion of the toxin and other proteins that convert from soluble to membrane-inserted states are discussed.

Access this article

Log in via an institution

Subscribe and save

Buy Now

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Similar content being viewed by others

Author information

Authors and Affiliations

  1. Department of Biochemistry and Cell Biology, Department of Chemistry, and the Institute for Cell and Developmental Biology, State University of New York at Stony Brook, Stony Brook, NY 11794-5215, USA, , , , , , US
    J.C. Sharpe & E. London

Authors

  1. J.C. Sharpe
    You can also search for this author inPubMed Google Scholar
  2. E. London
    You can also search for this author inPubMed Google Scholar

Additional information

Received: 10 March 1999/Revised: 22 June 1999

Rights and permissions

About this article

Cite this article

Sharpe, J., London, E. Diphtheria Toxin Forms Pores of Different Sizes Depending on Its Concentration in Membranes: Probable Relationship to Oligomerization.J. Membrane Biol. 171, 209–221 (1999). https://doi.org/10.1007/s002329900572

Download citation